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ISSN2038-5889
DOTTORATO DI RICERCA IN FISICA
UNIVERSITÀ DI MESSINA
ACTIVITY REPORT
2011
C/O DIPARTIMENTO DI FISICA FACOLTA‘ DI SCIENZE – UNIVERSITÀ DI MESSINA
Lorenzo Torrisi Editore
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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Coordinatore del Dottorato di Ricerca in Fisica
Prof. Lorenzo Torrisi
Editore
Lorenzo Torrisi
Assistenti
Paola Donato
Mariapompea Cutroneo
Rocco Vilardi
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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DOTTORATO DI RICERCA IN FISICA
UNIVERSITÀ DI MESSINA
ACTIVITY REPORT
2011
ISSN2038-5889
C/O DIPARTIMENTO DI FISICA FACOLTA‘ DI SCIENZE – Università di Messina
Viale F. Stagno D’Alcontres 312, 98166 S. Agata, Messina
Lorenzo Torrisi Editore
http://ww2.unime.it/dottoratofisica
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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INDICE GENERALE
Programma 2
a Giornata di Studio del Dottorato di Ricerca in Fisica dell’Università di Messina
6
2a Giornata di studio del Dottorato di Ricerca in Fisica dell’Università di Messina, 8 Nov. 2011
L. Torrisi
9
Valutazione nazionale della Qualità della Ricerca 2004-2010 (VQR)
M. C. Aversa
13
Dottorato di Ricerca e calcolo Scientifico
D. Magaudda
15
On the wavelength shift between near-field peak intensities and far-field peak cross sections in plasmonic
nanostructures
A. Cacciola
21
Mass quadrupole spectrometry applied to laser-produced plasmas and microwave ignited plasmas
F. Di Bartolo, L. Torrisi, S. Gammino, F. Caridi, D. Mascali, G. Castro, L. Celona, R. Miracoli, D. Lanaia and
R. Di Giugno
25
Fusion reactions in collisions induced by li isotopes on Sn targets
M. Fisichella, A. Di Pietro, A. Shotter, P. Figuera, M. Lattuada, C. Marchetta, A. Musumarra, M.G. Pellegriti,
C. Ruiz, V. Scuderi, E. Strano, D. Torresi, M. Zadro
31
Particle correlations at intermediate energies and the Farcos project
T. Minniti and Farcos/Chimera collaboration
33
Investigation on pseudoscalar meson photoproduction by electromagnetic probe M. Romaniuk, V. De Leo, F. Curciarello, G. Mandaglio, G. Giardina
37
Study of nuclear equations of state: the ASY-EOS experiment at GSI
S. Santoro for ASY-EOS collaboration
41
Premio APP per una Tesi di Dottorato
P. V. Giaquinta
47
PhD e mondo del lavoro: statistiche sul placement post – dottorato
P. Donato
49
An overview of research activities in the physics PhD course
F. Caridi, L. Torrisi
55
Enhanced optical fields for aggregation of metal nanoantennas and label free highly sensitive detection of
biomolecules
B. Fazio, C. D‘Andrea, V. Villari, N. Micali, O. Maragò, G. Calogero and P.G. Gucciardi
61
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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Missing resonances at the BGO-OD experiment
F. Curciarello, V. De Leo, G. Mandaglio, M. Romaniuk, G. Giardina
65
Resonant laser absorption and self-focusing effects producing proton driven acceleration from
hydrogenated structures
M. Cutroneo and L. Torrisi
71
Baryon spectroscopy by vector meson photo-production at BGO-OD experiment
V. De Leo, F. Curciarello, G. Mandaglio, M. Romaniuk , G. Giardina
77
Diode lasers for optical trapping applications
R. Sayed, G. Volpe, M. G. Donato, P. G. Gucciardi and O. M. Maragò
81
Interference with coupled microcavities
R. Stassi, O. Di Stefano, S. Savasta
85
Spectral dependence of the amplification factor in surface enhanced Raman scattering
C. D‘Andrea, B. Fazio, A. Irrera, P. Artoni, O.M. Maragò, G. Calogero and P.G. Gucciardi
89
Photoluminescence of a Quantum Emitter in the Center of a Dimer Nanoantenna: Transition from the
Purcell effect to Nanopolaritons
N. Fina, A. Ridolfo, O. Di Stefano, O. M. Maragò ,S. Savasta
93
Lateral Diffusion of DPPC and octanol in a Lipid Bilayer Measured by PFGE NMR Spectroscopy
S. Rifici
97
Chemical equilibration of the quark gluon plasma
F. Scardina, M. Colonna, V. Greco, M. Di Toro
101
A study about dynamic models on phospholipids
A. Trimarchi
105
Ultrafast optical control of light-matter interaction and of wave-particle duality
R. Vilardi, S. Savasta
109
Seminari (invited) del Dottorato di Ricerca in Fisica, Effettuati nel 2011
115
Organizzazione del Dottorato di Ricerca in Fisica dell’Università di Messina,
Ciclo (XXVI)
127
Pubblicazioni 2011 degli studenti del Dottorato di Ricerca in Fisica dell’Università di Messina
137
Foto 2a Giornata di Studio del Dottorato di Ricerca in Fisica dell’Università di Messina
145
Indice Autori
155
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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8 Novembre 2011
Biblioteca Centralizzata
V.le F. Stagno D’alcontres 31, S. Agata, Messina
http://ww2.unime.it/dottoratofisica
2a Giornata di Studio
del Dottorato di Ricerca in
Fisica dell’Università di
Messina
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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Comitato Organizzatore
Prof. L. Torrisi
Dr.ssa P. Donato
Dr.ssa M. Cutroneo
Dr. R. Vilardi
Comitato Scientifico
Prof. G. Carini
Prof. P. Giaquinta
Prof. G. Giardina
Prof. G. Maisano
Prof. D. Majolino
Prof. L. Torrisi
Giornata Organizzata dal
Collegio Docente
del Dottorato di Ricerca in Fisica
e sponsorizzata dall’ Università di Messina
Sito della Giornata di Studio:
Biblioteca Centralizzata della Facoltà di
Scienze dell’Università di Messina, Viale F.
Stagno D’alcontres 31, 98166 S.- Agata,
Messina
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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9.15 Relazioni di Apertura Saluti del Preside della Facoltà di Scienze MM.FF.NN.
Prof. G. Maisano, Direttore del Dipartimento di Fisica
Prof. L. Torrisi, Coordinatore del Dottorato di Ricerca
in Fisica
Prof. D. Majolino, Coordinatore dei CdL in Fisica e
Fisica Magistrale
Prof. F. Neri, Direttore Dip.to di Fisica della Materia
ed Ingegneria Elettronica
Prof.ssa M. C. Aversa, Delegata alla Ricerca
Scientifica e Tecnologica dell‘Università
Dr.ssa D. Magaudda Responsabile dell‘Area Sistema
Informativo per l‘Analisi dei Dati e Calcolo Scientifico
Dottorato Ciclo XXV Presiede: Prof. G. Carini
10.00 A. Cacciola (On the wavelength shift between
near-field peak intensities and far-field peak
cross-sections in plasmonic nanostructures)
10.20 F. Di Bartolo (Mass Quadrupole Spectrometry
applied To Laser-Produced Plasmas and
Microwave Ignited Plasmas)
10.40 M. Fisichella (Fusion reactions and neutron
transfer in collisions induced by Li isotopes on Sn
targets)
11.00 T. Minniti (Particle correlations to intermediate
energies and the Farcos Project)
11.20 M. Romaniuk (Investigation on pseudoscalar
meson photoproduction by electromagnetic probe)
11.40 S. Santoro (Study of nuclear equations of state:
the ASY-EOS experiment at GSI)
12.00 Interventi degli Enti di Ricerca Presiede: Prof. G. Giardina
Dr. G. Cuttone, Direttore dei LNS, Catania
Dr. C. Vasi, Direttore IPCF-CNR, Messina
Dr. A. Pagano, Direttore Sez. INFN, Catania
Prof. S. Albergo, Direttore del CSFNSM
Presiede: Prof. P. Giaquinta
Premiazione Tesi di Dottorato di Ricerca in
Fisica, Patrocinata dall‘Accademia Peloritana
dei Pericolanti
12.30 Dr. A. Ridolfo (Quantum Optical
Properties of strongly Coupled Systems)
Presiede Prof.: G. Mondio
15.00 Dr.ssa P. Donato, Manager Didattico PhD
(PhD e mondo del lavoro: statistiche sul
placement post-dottorato)
15.15 Dr. F. Caridi, Facoltà di Scienze – ME
(An overview of research activities in the physics
PhD course)
15.30 Dr.ssa B. Fazio, IPCF-CNR (Enhanced
optical fields for aggregation of metal
nanoantennas and label free highly sensitive
detection of biomolecules )
Ciclo XXVI- Presentazione posters 15.45 Presiede Prof. L. Torrisi
F. Curciarello (Missing resonances at the BGO-
OD experiment)
M. Cutroneo (Resonant laser absorption and self-
focusing effects producing proton driven
acceleration from hydrogenated structures)
V. De Leo (Baryon spectroscopy by vector meson
photoproduction at BGO-OD experiment)
R. Sayed (Diode lasers for optical trapping
applications)
R. Stassi (Interference with coupled
microcavities: optical analog of spin 2 rotations)
Ciclo XXIV- Presentazione posters 16.25 Presiede Prof. D. Majolino
C. D’Andrea (Spectral dependence of the
amplification factor in surface enhanced Raman
spectroscopy)
N. Fina (Photoluminescence of a quantum
emitter in the center of a dimer nanoantenna:
transition from the Purcell effect to
nanopolaritons)
S. Rifici (Structural changes of lipid bilayers by
the addiction of short-chain alcohols)
F. Scardina (Chemical equilibration of the
quark gluon plasma)
A. Trimarchi (A study about dynamic models
on phospholipids)
R. Vilardi (Ultrafast optical control of light-
matter interaction and of light wave-particle
duality)
17.15 Interventi di chiusura da parte del Collegio
Docente – Conlusione dei Lavori
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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Prof. L. Torrisi
2a GIORNATA DI STUDIO DEL DOTTORATO DI RICERCA IN FISICA
DELL’ UNIVERSITÀ DI MESSINA
MESSINA, 8 NOVEMBRE 2011
Lorenzo Torrisi
Coordinatore del Dottorato di Ricerca in Fisica
Dip.to di Fisica, Università di Messina
V.le F. Stagno D’Alcontres 31, 98166 S. Agata, Messina
La seconda giornata
di studio del Dottorato
di Ricerca in Fisica
dell‘Università di
Messina trova in questa
seconda manifestazione
un altro particolare
momento di riflessione
scientifica di notevole
rilevanza, di riunione
collegiale accademica,
meeting di discussione
su aspetti di Fisica,
consuntivi e
proponimenti, che
coinvolge i Dottorandi della Scuola, il Collegio
Docente, gli Organi competenti della Nostra Facoltà e
dell‘Università nonché delle istituzioni scientifiche che
collaborano col Dottorato stesso, come l‘Istituto
Nazionale di Fisica Nucleare e il Consiglio Nazionale
delle Ricerche.
Il Collegio Docente, la comunità dei fisici, quella dei
colleghi di altre aree scientifiche e tutti i nostri
collaboratori potranno cogliere l‘occasione di questa
giornata per informarsi sullo stato dei lavori del
Dottorato di Ricerca in Fisica, orgoglio della Nostra
Università. Mediante questo appuntamento sarà
possibile conoscere le tematiche delle ricerche in Fisica
che si stanno attualmente sviluppando presso il Nostro
Ateneo, i progetti che coinvolgono collaborazioni con
altre sedi universitarie, centri di ricerca e laboratori
esteri, le attività svolte nei laboratori di Messina e in
altre sedi collegate. Tali laboratori vedono
l‘avvicendarsi continuamente dei nostri dottorandi in
ricerche di ampio respiro internazionale e spesso
diventano loro sede di lavoro post-doc.
I risultati più innovativi che con essi vengono
ottenuti sono stati, e continuano ad esserlo, oggetto di
pubblicazioni su riviste ISI con ricadute non solo nel
mondo della ricerca e della didattica ma anche in
quello sociale. Molte ricerche svolte in seno al
dottorato sono infatti pubblicate su riviste ad alto
fattore di impatto, molte collaborazioni vengono
effettuate con gruppi di ricercatori dei migliori
laboratori europei ed extraeuropei, molti risultati
trovano applicazione in campo sanitario e ambientale e
molti nostri dottori di ricerca trovano occasione di
lavoro in questi centri di eccellenza.
Partecipare a questa giornata ci permetterà di
conoscere meglio le attività di ricerca di gruppi a noi
vicini, di una nuova generazione di giovani fisici, e ci
potrà permettere di instaurare un discorso scientifico
creativo e costruttivo con loro, un‘occasione che
almeno una volta all‘anno ha motivo di esistere.
Logo Università di Messina
Nel mio ruolo, colgo l‘occasione per ricordarvi che il
Dottorato di Ricerca rappresenta il massimo titolo per
la preparazione scientifica che l‘Università può
conferire ai propri studenti. Oltre la laurea breve, la
laurea magistrale, le Scuole di Specializzazione ed i
Masters, il Dottorato offre possibilità di apprendimento
uniche. Esso si basa non solo sulle lezioni di un
Collegio Docente altamente qualificato ed appropriato
ma anche su una periodica serie di seminari
specialistici tenuti in un contesto Nazionale ed
Internazionale che investono i vari Curriculum del
Dottorato. Attualmente 31 docenti fanno parte del
collegio, 17 sono i dottorandi, 4 i curricula di studio e
ogni mese due esperti sono invitati a tenere seminari
specialistici di interesse curriculare.
I campi di rilievo sono quelli della Struttura della
Materia, della Fisica della Materia Soffice e dei
Sistemi Complessi, della Fisica Nucleare e della Fisica
Applicata all‘Ambiente, ai Beni Culturali e al Settore
Bio-Medico. E‘ in questi ampi settori che il nostro
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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La ricerca scientifica
dottorando viene portato a svolgere attività di ricerca,
usufruendo di una serie di Laboratori altamente
adeguati nei quali ha l‘opportunità di operare dando un
proprio contributo. I laboratori dell‘Accademia delle
Scienze della Repubblica Ceca di Praga, l‘Istituto di
Fisica dei Plasmi e di Microfusione Laser di Varsavia, i
laboratori GSI di Darmstadt, i laboratori Nazionali
dell‘INFN, l‘Istituto di Ricerca Nucleare Ucraino INR,
l‘Istituto di Fisica Nucleare Skobeltsyn di Mosca e
quello JINR di Dubna, sono solo alcuni dei vari
laboratori di eccellenza con i quali il Nostro dottorato
può svolgere una continua attività di ricerca e avvalersi
di una collaborazione con scambio di studenti e
docenti. Collaborazioni rese solide attraverso accordi e
protocolli ufficiali che sono stati voluti da alcuni
componenti del Nostro Collegio Docente. A loro va un
plauso per queste collaborazioni che non nascono dal
nulla ma da un intenso, attivo e continuo lavoro,
spesso sottovalutato, grazie al quale il nostro Dottorato
può emergere e avere un respiro a livello internazionale
e l‘Università di Messina essere menzionata nel
mondo.
Laboratorio di fisica dei Plasmi Laser, Dip.to
Fisica, Messina
I dottorandi hanno la possibilità di essere inseriti in
progetti di ricerca di front-end, di partecipare a lavori
scientifici di prestigio e di redigere delle tesi inedite,
originali e utili. Per questo sono guidati durante il loro
percorso verso corsi e scuole di formazione
internazionali che permettono loro di ottenere una più
mirata specializzazione sulla tematica di loro maggiore
interesse. Ma il loro lavoro ha bisogno di essere
maggiormente conosciuto e divulgato. Ciò avviene non
solo attraverso le pubblicazioni di lavori scientifici ma
anche mediante altri canali, come questa giornata di
studio nella quale gli è consentito, di esprimersi e
dialogare per avere i giusti input e suggerimenti e un
maggiore sostegno durante la sua formazione,
necessari all‘ottenimento di maggiori riconoscimenti e
consensi scientifici. Ricordo ai dottorandi che ogni loro
risultato, seppur minimo, è prezioso e come in un
grande mosaico costituisce un piccolo pezzo che si
aggiunge a tanti altri che sono venuti e che verranno e
che permettono di ampliare le conoscenze umane.
Abituarsi a trasferire le proprie conoscenze, ad
intercalarle in problematiche più generali, a
completarle con altre al fine di poter estrapolare leggi e
teorie, è una attività che il dottorando andrà sempre più
approfondendo sia durante il dottorato di ricerca che
dopo, con l‘esperienza post-doc. La ricerca mette in
moto energie e stimoli di tale vitalità che il
meccanismo economico ne trae vantaggio, come una
macchina ben alimentata. L‘innovazione frutto della
ricerca ha dunque una ricaduta pratica e concreta anche
sulla ricchezza delle nazioni.
Ma proprio su questo punto, si impone qualche altra
mia considerazione che purtroppo ricalca quanto già
detto l‘anno scorso.
Ancora oggi in Italia la ricerca scientifica è, come è
noto, poco finanziata e i ricercatori sono mortificati dai
finanziamenti quasi inesistenti. Inoltre la crisi italiana
ed europea nel campo dell‘occupazione giovanile rende
difficile l‘utilizzo appieno delle capacità che il
dottorando ha appreso e spesso egli trova grosse
difficoltà di inserimento nel mondo della ricerca e del
lavoro post-doc. Sempre più spesso i nostri dottorandi
debbono purtroppo trasferirsi all‘estero regalando ad
altre realtà le esperienze acquisite. In questo contesto la
giornata di studio attuale vuole rappresentare una
denuncia alla nostra società ed ai nostri politici
cercando di sensibilizzarli maggiormente verso
l‘importanza della ricerca scientifica in uno stato
funzionale.
Tuttavia qualcosa si sta muovendo, visto che
recentemente il Ministro dell‘Istruzione,
dell‘Università e della Ricerca ha emanato un
regolamento recante i nuovi criteri generali per la
disciplina del dottorato di ricerca. Una meritata
attenzione che ci fa sperare in un futuro migliore, come
verrà tra poco approfondito dalla delegata alla Ricerca
Scientifica e Tecnologica dell‘Università di Messina,
Professoressa Maria Chiara Aversa e dalla
Responsabile dell‘Area Sistema Informativo per
La ricerca scientifica
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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Doctor of Phylosophy
l‘Analisi dei Dati e Calcolo Scientifico, Dottoressa
Dora Magaudda.
Inoltre tante iniziative sono in corso per agevolare il
finanziamento da parte della comunità europea di
specifici progetti di ricerca per i giovani post-doc.
Quest‘anno il Dottorato di Ricerca in Fisica ha
ricevuto solo due borse universitarie, una terza
l‘abbiamo ottenuta grazie ai fondi INFN, purtroppo
non possiamo avere di più, neppure per studenti
stranieri non europei. E‘ un peccato che il nostro
dottorato di ricerca, debba subire un decremento di
elementi, nonostante il numero crescente di aspiranti
studenti sia della sede che da fuori sede.
Ma noi non ci fermeremo per queste difficoltà
perché crediamo profondamente nella formazione e
nella Ricerca che in Italia può realizzarsi al meglio
anche con le avversità che si spera essere solo
momentanee. E per questo ideale oggi siamo qui e
presenteremo le nostre attività che reputiamo essere
alla base della nostra esperienza di fisici. E‘ grazie a
questi ideali che il nostro Dottorato può permettere le
sue formative e molteplici attività e mira a promuovere
e premiare i giovani con le migliori redazioni di Tesi e
di risultati conseguiti, come oggi sarà evidenziato.
1° Report del Dottorato di Ricerca in Fisica,
2010
Vi ricordo che, secondo quanto approvato dall‘
ultima riunione del Collegio docente, che i dottorandi
del secondo anno dovranno presentare un intervento
sul loro lavoro di tesi mentre i dottorandi del primo e
terzo anno un poster e un sintetico sunto. I lavori
scientifici che i dottorandi esporranno in questo
incontro, sia come contributo orale che come poster,
nonché i vari interventi che gli invitati presenteranno,
saranno raccolti nel secondo Report del Dottorato di
Ricerca in Fisica dell‘Università di Messina, che sarà
pubblicato a breve e che rappresenterà un altro
documento duraturo nel tempo, una vera e propria
pubblicazione per il dottorando, e una pubblicazione
annuale del Dottorato, depositata presso la nostra
biblioteca, con numero ISSN già assegnato.
RingraziandoVi per l‘attenzione dedicatami, auguro
a tutti voi, colleghi, dottorandi e partecipanti, un buon
lavoro.
Il Coordinatore del Dottorato di Ricerca
Prof. Lorenzo Torrisi
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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VALUTAZIONE NAZIONALE DELLA QUALITÀ DELLA RICERCA
2004-2010 (VQR)
Maria Chiara Aversa
Delegata del Rettore dell’Università di Messina per la ricerca in area scientifico-tecnologica
Il 7 novembre 2011 è stato pubblicato il bando
ufficiale di partecipazione alla Valutazione della
Qualità della Ricerca 2004-2010 (VQR 2004-2010)
(http://www.anvur.org/sites/anvur-
miur/files/bando_vqr_def_07_11.pdf).
L‘inizio dell‘esercizio di valutazione
nazionale era atteso da tempo, ma probabilmente esso è
stato rinviato più volte come conseguenza del
passaggio dal Comitato Nazionale per la Valutazione
del Sistema Universitario (CNVSU) all‘Agenzia
Nazionale di Valutazione del sistema Universitario e
della Ricerca (ANVUR). All‘epoca della pubblicazione
del DM n. 8 del 19 marzo 2010 avente per oggetto
―Linee guida VQR 2004-2008‖
(http://civr.miur.it/vqr_decreto.html) il progetto di
valutazione nazionale era limitato a cinque anni e
l‘acronimo VQR corrispondeva appunto a
―Valutazione Quinquennale della Ricerca‖. A causa del
notevole postergarsi della data d‘inizio, è stato deciso
di includere altri due anni, e si è giunti così al
significato attuale dell‘acronimo.
Figura 1
A metà del 2011 si è insediato il consiglio
direttivo dell‘ANVUR (figura 1) costituito da 7
componenti, tutti di estrazione universitaria, presieduto
da Stefano Fantoni, professore ordinario di FIS/04
(Fisica nucleare e subnucleare) della SISSA di Trieste,
cui si affiancano professori appartenenti alle aree 06
(Scienze mediche), 07 (Scienze agrarie e veterinarie),
09 (Ingegneria industriale e dell‘informazione), 13
(Scienze economiche e statistiche) e 14 (Scienze
politiche e sociali). La figura 1 è congegnata in maniera
da mettere in evidenza la distribuzione geografica delle
strutture universitarie da cui provengono i 7
componenti del consiglio direttivo, e la distribuzione di
genere (cerchi azzurri/rosa): sono solo 2 le donne nel
consiglio direttivo, uniche 2 rappresentanti della
macroarea umanistica, Fiorella Kostoris Padoa
Schioppa e Luisa Ribolzi, entrambe in pensione, la
prima dall‘Università di Roma La Sapienza e la
seconda dall‘Università di Genova. Si tratta di dati che
dovrebbero suscitare qualche riflessione.
La VQR 2004-2010 è coordinata da Sergio
Benedetto (figura 1), professore ordinario di ING-
INF/03 (Telecomunicazioni) presso il Politecnico di
Torino. Il bando di partecipazione alla VQR del 7
novembre 2011 ha lievemente modificato il contenuto
dell‘art. 5 del DM n. 8 del 19 marzo 2010 avente per
oggetto ―Linee guida VQR 2004-2008‖: in particolare
(a) gli articoli scientifici da proporre per la valutazione
potranno essere stati pubblicati anche su riviste prive di
ISSN e (b) potranno essere proposte anche le
traduzioni. Visto che già dal 2010 l‘Ateneo di Messina
prende in considerazione per le proprie valutazioni
interne soltanto i prodotti citati dall‘art. 5 di cui sopra,
bisognerà proporre al Senato accademico un‘eventuale
delibera di adeguamento.
L‘ANVUR ha inoltre pubblicato la lista dei
presidenti dei Gruppi di Esperti della Valutazione
(GEV) (figura 2), uno per ciascuna delle 14 aree CUN.
Entro la fine di novembre verrà approvata e pubblicata
la composizione dei 14 GEV insieme con i criteri
sottostanti alla selezione degli esperti. In analogia alla
1, anche la figura 2 è congegnata in maniera da mettere
in evidenza la distribuzione geografica delle strutture di
ricerca da cui provengono i 14 presidenti dei GEV, e la
distribuzione di genere: ancora una volta soltanto 2
donne, Clara Nervi, professore straordinario presso
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
14
l‘Università di Roma La Sapienza per l‘area 05
(Scienze biologiche) e Maria Teresa Giaveri per l‘area
10 (Scienze dell'antichità, filologico-letterarie e
storico-artistiche), attualmente professore ordinario
presso l‘Università di Torino e che ha insegnato
―Lingua e letteratura francese‖ presso l‘Università di
Messina nel periodo 1994-1997.
E‘ necessario evidenziare le scadenze
temporali che l‘Università dovrà rispettare nel prendere
parte all‘esercizio della valutazione nazionale della
ricerca:
a) certificazione elenchi CINECA/MIUR
soggetti valutabili (30 dicembre 2011);
b) verifica elenchi doc, postdoc, assegnisti,
specializzandi area medica (06) (31 marzo
2012);
c) trasmissione informazioni mobilità nel
settennio (31 marzo 2012);
d) trasmissione prodotti di ricerca (30 aprile
2012);
e) rapporto di autovalutazione (NV/Rettore) (31
maggio 2012);
f) trasmissione brevetti, spin-off, finanziamenti,
ecc… + elenco nuovi Dipartimenti con
afferenti (31 maggio 2012).
Figura 2
Il rapporto finale dell‘ANVUR dovrebbe essere
disponibile entro il 30 giugno 2013.
Tra le innovazioni più significative e gli
aspetti più rilevanti del bando VQR del 7 novembre
2011 rispetto ai documenti precedentemente a
disposizione, si segnala:
a) è stato eliminato il coefficiente di
proprietà per i prodotti presentati da più di
una struttura;
b) è stato eliminato l‘indicatore di proprietà
dei prodotti eccellenti;
c) è stato eliminato il vincolo per le strutture
di rispettare l‘ordine di priorità dei
prodotti indicato dagli autori;
d) globalmente su tutte le aree, almeno la
metà più uno dei prodotti saranno
sottoposti a peer review;
e) la precedente valutazione VTR 2001-
2003 si è basata su circa 17.000 prodotti,
mentre l‘attuale VQR è dimensionata
intorno a 200.000 prodotti.
Appare opportuno concludere questo
contributo citando testualmente la frase di chiusura del
messaggio di accompagnamento
(http://www.anvur.org/?q=schema-dm-vqr-definitivo)
del bando VQR del 7 novembre 2011 a firma di Sergio
Benedetto (figura 1): ―Vi rinnovo l‘augurio di buon
lavoro, nella certezza che insieme affronteremo e
risolveremo i molti problemi che si presenteranno
strada facendo‖. Effettivamente solleva qualche
perplessità questa mal celata mancanza di sicurezza
nella effettività delle procedure, ma, ancora una volta,
….. l‘Università italiana ce la farà!
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
15
DOTTORATO DI RICERCA E IL CALCOLO SCIENTIFICO
Dora Magaudda
Sistemi Informativi per l’Analisi dei dati d’Ateneo e Calcolo Scientifico CECUM
Università di Messina
Il Dottorato di Ricerca è stato istituito in Italia solo
nel 1980 (legge 21 febbraio 1980, n. 28, D.P.R. 11
luglio 1980, n. 382), e rappresenta il più alto grado
d‘istruzione ottenibile nel sistema universitario italiano
e conferisce la qualifica di ―Dottore di Ricerca‖, è il
più alto titolo accademico conferibile nell‘ordinamento
della Repubblica Italiana.
Nel corso degli anni, l‘andamento di tali corsi è stato
attentamente valutato non solo dal MiUR ma anche da
tutti i sistemi ufficiali di valutazione, compresi la
CRUI, il CNVSU e i Nuclei.
La CRUI definisce ―il Dottorato come il terzo livello
di formazione universitaria ed è il grado più alto di
specializzazione offerto dalle Università sia per le
carriere accademiche e di ricerca sia per quelle nel
mondo produttivo, in particolare di quello attento
all‘innovazione. È pertanto necessario che il valore del
dottorato sia alto e, come tale, riconosciuto
internazionalmente. La formazione dottorale non può
che essere fatta con e per la ricerca e quindi richiede,
per il suo espletamento, una documentata attività di
ricerca ad alto livello….
Il dottore di ricerca deve diventare il prodotto finale
e più specializzato che l‘università dà alla società per
una classe dirigente preparata e consapevole‖.
Il nuovo statuto dell‘Università di Messina ha posto
l‘istituzione dei Dottorati di Ricerca tra i suoi interessi
primari: tra gli organi di Governo è stato inserito, tra
gli altri, il Collegio dei Coordinatori delle Scuole di
Dottorato.
Problematiche rilevate sui dottorati di ricerca
e indicazioni ministeriali per le loro soluzioni
Già nel 2002-2003, il CNVSU auspicava che fossero
incoraggiati alcuni comportamenti volti a
salvaguardare le finalità del Dottorato di Ricerca,
chiedendo ai Nuclei di Valutazione di monitorarle:
a) contenimento dell’eccessiva frammentazione,
ciò potrebbe infatti comportare:
a. una docenza e un programma formativo
inadeguati
b. uno scarso numero d‘iscritti e di borse.
Così come con la 509 si è avuta una larga
proliferazione di Corsi di Studio non facilmente
spendibili nel mondo del lavoro, anche per i Dottorati
di Ricerca ci si è trovati di fronte ad una situazione
simile. Per tali ragioni, il CNVSU è sempre stato
favorevole a iniziative di accorpamento, che portino
alla costituzione di Scuole di Dottorato.
Questo è un compito abbastanza semplice per i
Nuclei, laddove si riscontrino dottorati che nel loro
piano di studi abbiano aree disciplinari sovrapponibili;
ma quando questa sovrapposizione non esiste o
richiederebbe conoscenze approfondite, diviene
necessaria una peer review che non è sempre
effettuabile da parte dei Nuclei stessi.
b) concentrazione in un‘unica sede delle attività
didattiche dei dottorati consorziati.
Questa valutazione è abbastanza semplice per i
Nuclei
c) opportuna ricerca di fonti esterne di
finanziamento, onde consentire la creazione di figure
professionali appropriate a creare sbocchi
occupazionali, laddove, soprattutto, le fonti di
finanziamento esterne siano erogate da Aziende
interessate alla ricerca. Altrimenti, c‘è il rischio che il
titolo possa essere considerato come una semplice
estensione del percorso formativo della laurea.
Questa valutazione è abbastanza semplice per i
Nuclei
d) creazione di una spinta all‘internazionalizzazione,
con la creazione di percorsi preferenziali per l‘accesso
di studenti stranieri o di altre Università, tramite
l‘istituzione di borse apposite e incentivando la
collaborazione con Atenei stranieri.
Anche questa valutazione è abbastanza semplice per
i Nuclei, ma solo in fase di Consuntivo, in quanto, nella
fase di Attivazione o di Rinnovo di un Dottorato di
Ricerca, i collegamenti con altre Università ed Enti,
italiani o stranieri, non possono ancora essere
formalizzati, dato che la valutazione del Nucleo
avviene prima della decisione della Governance
dell‘Ateneo sui dottorati da attivare e sul numero di
borse d assegnare ad ognuno.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
16
Negli anni passati, a partire dall‘esercizio 2002, si è
avuta una ripartizione del 20% di finanziamento alle
Università per i Dottorati di Ricerca che rispondessero
ad alcuni requisiti precisi, che sono stati recepiti anche
dal Nucleo di Valutazione dell‘Università di Messina e
saranno discussi in seguito.
Essendo stata concessa grande autonomia alle
università che decidono:
• L‘istituzione dei corsi di dottorato
• Le modalità di accesso e conseguimento del
titolo
• Gli obbiettivi formativi ed il relativo
programma di studio
• La durata
• Il contributo per l‘accesso e la frequenza
• Le modalità di conferimento e l‘importo delle
borse di studio.
il problema che si è prospettato è stato della
impossibilità di definire in maniera chiara e univoca
per tutte le Università i termini di attivazione dei
Dottorati.
I Nuclei si sono trovati di fronte al problema di
standardizzare (almeno a livello di Ateneo) le
valutazioni dei Dottorati di Ricerca.
ll Nucleo di Messina ha stabilito che, laddove fosse
esprimibile con un indicatore un requisito ministeriale,
di considerarlo come indispensabile per l‘assegnazione
di un valore, affinché l‘Ateneo potesse concorrere a
questa quota di finanziamento
La legge 30 Dicembre 2010, n. 240
Con l‘introduzione della nuova legge del 30
Dicembre 2010, n. 240, si è arrivati alla proposta di una
nuova e più ampia visione dei corsi di Dottorato,
rivisitata anche in base alle esperienze pregresse.
Anche in questo caso, si pone l‘accento sulla
partecipazione dei Dottorandi ai gruppi e ai progetti di
ricerca e si richiede di esaminare la necessità di una
valutazione periodica della produzione scientifica dei
dottorandi. Questa valutazione si dimostra piuttosto
problematica sin da oggi, in quanto tra le varie aree
scientifiche-disciplinari, e soprattutto tra le macro-aree
umanistiche e scientifiche, si ha una notevole
differenziazione nella preparazione alla ricerca dei
dottorandi stessi. Un esempio per tutti è quello dei
dottorati in aree letterarie, dove il dottorando prepara la
sua tesi, che deve essere inedita, in genere tramite una
monografia e non tramite più articoli su rivista o altro
come avviene nelle aree scientifiche. Questo modus
operandi porta alla pubblicazione della tesi solo dopo
l‘esame finale di Dottorato: ne consegue una forte
difficoltà per i Nuclei nella valutazione annuale dei
consuntivi dei dottorati di ricerca di questo tipo.
Un‘altra differenza fondamentale si può riportare a
proposito della numerosità degli autori: in generale,
nelle pubblicazioni scientifiche, si hanno
collaborazioni tra più settori scientifici disciplinari e/o
più macro-aree, ne consegue che il numero di autori
può essere molto superiore a quello di coloro che
hanno produzioni eminentemente umanistiche (in
generale un solo autore).
Il Nucleo di Messina ha recepito le difficoltà espresse
dai Coordinatori delle Aree Umanistiche, suddividendo
i risultati delle valutazioni nelle due macro-aree
distinte; ma nonostante ciò esistono problematiche non
risolvibili semplicemente con una standardizzazione
del calcolo degli indicatori.
Un altro punto importante cui si fa espressa
menzione è che non può essere accettabile la
consecuzione del titolo di dottore di ricerca oltre i 30
anni, dato che dovrebbe essere possibile entrare nella
fase post-doc o lasciare l‘Università attorno ai 26-27
anni, evitando un inserimento tardivo nella realtà
professionale.
Il Nucleo di Messina probabilmente modificherà il
calcolo dell‘indicatore, per quanto lo abbia già fatto in
passato differenziando i punteggi dei dottorandi senza
borsa, con borsa e con borsa di altra amministrazione.
E‘ necessario sottolineare che la legge non prevede
risorse sufficienti per la propria applicazione, quindi
neanche per il dottorato di ricerca: allo stato attuale il
taglio di oltre il 30% verificatosi nell‘ultimo triennio
potrebbe arrivare a raggiungere circa il 50% dei posti
messi a concorso. Si presume che i circa 12.000
dottorandi possano ridursi a meno di 6.0001: ciò
significherebbe una consistente riduzione del sistema
dell‘Alta Formazione.
Si ipotizza, dal testo della legge, che si avrà una forte
incentivazione dell‘istituzione dei Dottorati senza borsa
(senza, per altro, consentire almeno una notevole
riduzione delle tasse di iscrizione) anche se
l‘interpretazione della disciplina sulle borse di studio è
controversa, pur essendo rimodulato l‘importo minimo
della borsa stessa, che in Italia, rispetto ad altri paesi
europei è molto contenuto.
L’Art. 7 – Interventi di cooperazione interuniversitaria internazionale strutturata prevede che solo 4.000.000€ vengano destinati a consolidare e incentivare interventi di università italiane, di studenti, laureati e dottorandi provenienti da Paesi extraeuropei
1 Questi dati sono messi a disposizione dall‘ANDI
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
17
in linea con le politiche ministeriali di cooperazione internazionale.
Il numero minimo di borse di dottorato passa da 3 a
6: ma non è chiaro se quest‘ultimo numero è da
intendersi solo per le Scuole di Dottorato o per i corsi
di dottorato. In quest‘ultimo caso, quelli attivabili
presso ciascuna Università dovrebbero essere molto
meno numerosi, soprattutto nei casi in cui la
reperibilità di risorse esterne, fortemente dipendente,
com‘è ovvio, dal bacino geografico su cui insiste la
singola Università, è problematico.
Il Nucleo, anche in questo caso, può giudicare il
numero di borse solo dopo la loro assegnazione, quindi
in fase di consuntivo
La legge chiede anche una valutazione dell‘impatto
professionale del titolo.
Il precedente Nucleo di Valutazione aveva inserito
nelle sue valutazioni una tabella in cui si chiedeva ad 1
anno, a due e a tre quale fosse l‘attività lavorativa
intrapresa dal dottorando e se fosse coerente con il
percorso di studi. I dati ricevuti in risposta sono
piuttosto scarni e quindi non significativi, perché non
sempre era possibile contattare i dottorandi stessi
Attivazione dei corsi di dottorato e ruolo del
nucleo
Come si è già detto, i Nuclei di Valutazione hanno
dovuto, nel corso degli anni, giudicare i Dottorati di
Ricerca in base a determinati requisiti, che la 240 ha
reso più stringenti. Il Nucleo di Messina ha concepito
una scheda di richiesta rinnovo/nuova attivazione ed
una di Consuntivo che contenesse tutte le informazioni
necessarie alla valutazione dei Dottorati di Ricerca. In
tal modo, avrebbe potuto effettuare le sue valutazioni
nella maniera più corretta in base alle indicazioni
ministeriali.
A tale scopo, ha chiesto alla propria Referente
Informatica, capo Area Sistemi Informativi per
l‘Analisi dei dati d‘Ateneo e Calcolo Scientifico, la
creazione di un software apposito. Il risultato è stato
considerato molto soddisfacente sia dal Nucleo che
dall‘utenza, per la semplicità d‘uso e le facilities
inserite che lo rendono intuitivo ed efficace.
In sintesi il software si compone di sei parti
fondamentali:
1. Compilazione della scheda di richiesta
rinnovo/nuova attivazione da parte del Coordinatore
2. Compilazione della scheda di consuntivo per
ogni ciclo attivo da parte del Coordinatore e dei
Dottorandi
3. Attestazione della correttezza delle
dichiarazioni informatizzate da parte dell‘Ufficio
Dottorandi che convalida, in base al cartaceo presentato
dai Coordinatori, quanto da loro stessi dichiarato2
4. Attestazione della validità delle dichiarazioni
dei dottorandi da parte del Nucleo di Valutazione3
5. Procedura automatizzata di calcolo dei
punteggi degli indicatori4
Procedura di visualizzazione dei punteggi degli
indicatori di tutti i dottorati. La procedura consente la
visualizzazione di tutti i dettagli ed è visibile a tutti i
Coordinatori.
Gli indicatori considerati sono 8 e rispecchiano, dove
possibile, le richieste del Ministero in maniera
dettagliata, ovvero i criteri concordati con la
Governance d‘Ateneo laddove quelli ministeriali siano
nebulosi o non ben descritti.
Rispetto ai primi calcoli, sono state apportate
modifiche delle quali via via si sentiva il bisogno,
dettate sia dalle differenze tra la conduzione dei
dottorati di ricerca (per esempio tra le due macro aree
Umanistica e Scientifica) sia dalle le diverse necessità
di conduzione dei dottorati, dovute a svariati motivi5:
tali differenziazioni sono state discusse durante alcune
riunioni con i Coordinatori di Dottorato.
Particolare attenzione è stata posta nella valutazione
dei prodotti della ricerca, resa possibile grazie alla
presenza del Catalogo di Ateneo informatizzato, che è
stato lo strumento principe per poter creare il software
necessario. Anche in questo caso, la valutazione di tali
prodotti è stata stabilita, una prima volta e
successivamente modificata, di concerto con la
Governance dell‘Ateneo.
E‘ importante sottolineare come alcune decisioni
siano state oggetto di critiche in quanto alcuni
Coordinatori trovavano i criteri troppo stretti per le
esigenze della loro Area. Ma anche queste perplessità
sono state considerate e in parte risolte nell‘ambito
della forte collaborazione tra il Nucleo e la Governance
dell‘Ateneo.
2 Attestati dei professori di altri Atenei presso i quali si sono
recati i dottorandi, attestazione dell‘incremento delle borse
per soggiorni all‘estero, lettere di partecipazione esclusiva di
un docente italiano al dottorato, curricula dei docenti stranieri
e italiani non di Messina (per i Messinesi esiste il Catalogo di
Ateneo che è stato uno strumento indispensabile per il buon
funzionamento dell‘impianto delle schede informatizzate). 3 Si tratta di convalidare o meno le dichiarazioni che talvolta
sono inserite per inesperienza, ma che non possono dare adito
a calcoli per i punteggi degli indicatori, quali, ad esempio, le
ore impiegate nella ricerca o negli incontri con il
Coordinatore e/o i tutor per la preparazione della tesi. 4 La procedura è del tutto indipendente dalle altre, per
consentire l‘effettuazione di modifiche nei calcoli nel modo
più semplice. 5 Si pensa ai periodi di permanenza all‘estero che, in
generale, danno adito a punteggio solo se sono di almeno tre
mesi, mentre per gli scavi archeologici e la permanenza sulle
navi scendono a 1 mese.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
18
Per una totale trasparenza del proprio operato, il
Nucleo ha inoltre richiesto che il software, alla
chiusura del periodo di richiesta di Rinnovi e o Nuove
Attivazioni e delle convalida amministrative6,
permettesse a tutti i Coordinatori la visione dettagliata
dei calcoli degli indicatori di tutti i Dottorati.
Si può ragionevolmente affermare che quello
dell‘Ateneo di Messina è stato, in Italia, il primo
impianto logico e software completo che ha consentito
la formalizzazione delle valutazioni sui Dottorati di
Ricerca: molte altre Università hanno, infatti, seguito
un modello molto simile. Nel Dicembre 2008 la
procedura è stata presentata nel convegno tenutosi a
Padova cui hanno partecipato tutti i Nuclei di
Valutazione. Purtroppo però, nonostante le richieste
ricevute, il nostro Ateneo non è stato in grado di fornire
tale software ad altre Università.
Un ulteriore punto a favore del lavoro svolto, è la
dedizione con cui il Prof. Mondello si è dedicato alla
valutazione della correttezza delle dichiarazioni nelle
schede ed a suggerimenti volti al miglioramento ed alla
semplificazione della procedura; per la parte operativa
sento il bisogno di ringraziare la serietà e la
professionalità del Dott. Marco Todaro e dell‘Ing.
Fabrizio De Gregori, che, con la procedura menzionata,
hanno consentito un notevole risparmio economico alla
nostra Università.
Il software si riferisce a due fasi distinte della
valutazione dei dottorati di ricerca: quella della
richiesta di Rinnovo/nuova Attivazione e quella di
Consuntivo, dove, al di là di alcune informazioni
fornite dai Coordinatori, ogni Dottorando indica il
percorso formativo svolto e il risultato delle sue
ricerche.
Come si è già detto gli indicatori sono 8, ed ognuno di
essi serve a quantificare una delle richieste ministeriali,
comprese quelle della 240, per la quale basterà
modificare soltanto il modulo di calcolo dei punteggi:
1. Numerosità del Collegio Docenti
7
2. Produttività Scientifica del Coordinatore
3. Produttività Scientifica pro capite del Collegio
Docenti
4. Accordi di collaborazione per lo svolgimento
di esperienze in un contesto di attività lavorative o per
lo svolgimento di stage in sedi di ricerca qualificate
straniere o italiane
5. Posti di dottorato aggiuntivi rispetto alle borse
finanziate dall‘Ateneo
6 Egregiamente effettuate dall‘Ufficio Dottorati che non si
potrà mai ringraziare abbastanza. 7 Il collegio docenti può essere formato solo dai docenti
indicati come tali dal MiUR.
6. Esistenza di un piano formativo formalizzato e
documentato
7. Produttività Scientifica di Ricerca pro capite
dei Dottorandi
8. Contesto Scientifico (Progetti di ricerca)
Nella tabella seguente si mostrano le differenze tra la
vecchia legislazione, quanto richiesto dalla L.240 e
l‘impianto logico, nelle schede del Nucleo, per il
calcolo degli indicatori:
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
8 ordinari e associati del/i settore/i concorsuali o SSD oggetto del corso, attivi in ricerca, ovvero, nei settori è opportuno, di esperti di elevata qualificazione di numero non superiore a quello dei docenti) 9 Art.5, comma 1, punto a dello Schema di decreto del MiUR ― Regolamento recante criteri generali per la disciplina del Dottorato di ricerca‖ del 27/09/2011 10 Per attivo si intende un professore che abbia pubblicato almeno tre prodotti della ricerca negli ultimi 3 anni ovvero, se dell‘aria umanistica, almeno 1 monografia. 11 Il Professore Ordinario attivo vale 1 punto, il professore associato attivo vale 0,7 punti, il ricercatore attiva vale 0,5 punti. Il Professore non attivo non da adito a punteggio. 12 I coordinatori nazionali o locali devono essere dell‘Università di Messina 13 Posti di Dottorati aggiuntivi rispetto alle borse d‘Ateneo: borse finanziate dalla comunità europea, PON, PRO, POM, Enti pubblici e/o privati, PRIN, FIRB, FSG, posti attivati con mantenimento dello stipendio
dell‘amministrazione originaria. 14 In generale il soggiorno in Italia dovrà essere di almeno 3 mesi, mentre per quelli all‘estero in sono valutati in quota parte ai 3/1 mese (v. nota 5) solo se vi sia un incremento della borsa.
Requisiti Ministeriali Precedenti Requisiti Ministeriali L. 240 Indicatore corrispondente Scheda in cui si trovano le
informazioni Valutato
la presenza nel collegio dei docenti di un congruo
numero di professori e ricercatori dell'area scientifica di riferimento del corso.
Non meno di 7 docenti per l’attivazione
Non meno di 10 per il 20% del finanziamento
Collegio docenti formato almeno da 188 professori9
attivi10
INDICATORE 1
Numerosità del Collegio Docenti11
Richiesta Rinnovo /nuova
Attivazione SI
la disponibilità di adeguate risorse finanziarie Non sono stabiliti in modo
esplicito
INDICATORE 8
Contesto Scientifico (Progetti PRIN, FIRB finanziati e/o finanziabili e Progetti
della Comunità Europea Finanziati12)
Richiesta Rinnovo /nuova
Attivazione SI
la disponibilità di specifiche strutture operative e scientifiche per il corso e per l’attività di studio e di
ricerca dei dottorandi
Non sono stabiliti in modo
esplicito Numero massimo di dottorandi compatibili con le strutture organizzative
Richiesta Rinnovo /nuova
Attivazione NO
la previsione di un coordinatore responsabile
dell’organizzazione del corso
Non cambia nulla rispetto alla
normativa precedente INDICATORE 1
Coordinatore. Non è possibile inserire una scheda senza un Coordinatore Richiesta Rinnovo /nuova
Attivazione SI
la previsione di un collegio di docenti e di tutori in
numero proporzionato ai dottorandi: non veniva
specificato però il significato di “congruo”
Collegio docenti formato almeno da 18 professori8, 9, 10
INDICATORE 1
Collegio Docenti
Richiesta Rinnovo /nuova
Attivazione SI
la previsione di un collegio di docenti e di tutori con documentata produzione scientifica nell’ultimo
quinquennio nell’area di riferimento del corso
Non cambia nulla rispetto alla normativa precedente
INDICATORE 2 e 3
Produzioni scientifiche del Coordinatore e del Collegio Docenti10 Richiesta Rinnovo /nuova
Attivazione SI
la possibilità di collaborazione con soggetti pubblici o privati, italiani o stranieri, che consenta ai dottorandi
lo svolgimento di esperienze in un contesto di attività
lavorative
Sono auspicati e se ne chiede l‘incremento, ma non vengono
fornite adeguate risorse
finanziarie.
INDICATORE 4
INDICATORE 513
Periodo formativo all‘estero
Accordi di collaborazione / convenzioni per lo svolgimento di esperienze in contesto di attività lavorative
Forme di collaborazione per lo svolgimento di esperienze in contesto di attività
lavorative non formalizzate14
Schede Consuntivo dei singoli
Dottorandi SI
la previsione di percorsi formativi orientati all'esercizio di attività di ricerca di alta qualificazione presso
università, enti pubblici o soggetti privati
Sono auspicati e se ne chiede
l‘incremento, ma non vengono
fornite adeguate risorse finanziarie.
INDICATORE 6
Programma formativo, modalità di svolgimento e finalità del corso
Obiettivi formativi orientati alla ricerca e tematiche di ricerca Indirizzi e tematiche di ricerca
Schede Consuntivo dei singoli
Dottorandi SI
l’attivazione di sistemi di valutazione relativi alla
permanenza dei requisiti di cui al presente comma
Non sono specificati meglio
neanche nella 240 INDICATORE 7
Produttività scientifica pro-capite dei dottorandi Schede Consuntivo dei singoli
Dottorandi SI
l’attivazione di sistemi di valutazione relativi alla rispondenza del corso agli obiettivi formativi di cui
all’articolo 4
Non sono specificati meglio
neanche nella 240
Modalità di valutazione periodica della preparazione dei dottorandi al fine della
prosecuzione del corso Richiesta Rinnovo /nuova
Attivazione NO
l’attivazione di sistemi di valutazione relativi alla
rispondenza del corso agli obiettivi formativi in relazione agli sbocchi professionali, al livello di
formazione dei dottorandi
Non sono specificati meglio neanche nella 240
Sbocchi professionali previsti Richiesta Rinnovo /nuova
Attivazione NO
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
20
Calcolo scientifico
A proposito della Ricerca Scientifica, e quindi anche
in relazione alla produttività scientifica pro-capite dei
dottorandi, è importante fare un ulteriore discorso.
Quale Responsabile dell‘Area Sistemi Informativi per
l‘Analisi dei dati d‘Ateneo e Calcolo Scientifico,
gestisco, validamente coadiuvata dall‘Ing. Sciacca e dal
Dott. Lo Re, il Settore di Calcolo Scientifico del
CECUM, mettendo a disposizione dei Ricercatori
dell‘Ateneo un insieme di risorse di calcolo piuttosto
consistente:
il cluster eneadi, costituito da sei server HP Integrity
quadriprocessori e da un server HP ProLiant
biprocessore per un totale di 26 CPU. Nello stesso rack
si trovano i server HP ProLiant che eseguono Windows
Server 2003 e consentono all‘utenza l‘uso dei
programmi MATHLAB e MATEMATICA, utilizzabili
direttamente dal portale di calcolo. Il server Xanto
(DL360), invece, insieme ai due server Voltumna
(SUNBLADE100) e Larsthurms (SUNBLADE2000)
sono utilizzati per la gestione del sito e dei software del
Settore di Supporto al Nucleo di Valutazione della
stessa area. Per quanto riguarda il dimensionamento di
queste ultime apparecchiature è necessario dire che
esse erano state acquisite per un numero di accessi
piuttosto limitato, in quanto, fino al 2007, il software a
disposizione del Nucleo di Valutazione era piuttosto
limitato. Da quando sono state sviluppate le procedure
principali delle richieste di Attivazione / Rinnovi dei
Dottorati di Ricerca e di Valutazione della Didattica
(arrivati rispettivamente alle versioni 5.0 e 2.7), il
bacino di utenza si è allargato a tutti i Coordinatori dei
Dottorati di Ricerca, ai Dottorandi per ciò che concerne
la prima procedura, ai Referenti di Facoltà, a tutti i
Docenti e gli studenti per ciò che riguarda la
Valutazione della Didattica, per un totale di oltre 2.000
utenze potenzialmente concorrenti;
Il cluster TriGrid, formato da un insieme di 28 lame
IBM LS20 e 21;
Nei due sistemi è installato il software LSF (Load
Sharing Facility) e librerie per il calcolo parallelo.
In generale l‘uso delle risorse offerte dal Settore di
Calcolo Scientifico viene effettuato da parte di un
gruppo ormai consolidato di utenti, il cosiddetto
gruppo storico, ma ad essi se ne stanno via via
aggiungendo altri che hanno iniziato a sfruttarle per le
proprie attività di ricerca o per altri progetti15
. In
15
Dal 2010 il Dipartimento di Ingegneria Civile partecipa ad
un progetto di ricerca europeo sullo sviluppo di tecnologie
sostenibili innovative per l‘energia, dal titolo
―THermoacoustic Technology for Energy Applications‖
(THATEA, http://www.thatea.eu/); il progetto è coordinato
dall‘Energy Research Centre of the Netherlands (ECN) e
quest‘ottica le risorse offerte dal Settore di Calcolo
Scientifico si sono rivelate molto significative, tenuto
conto che sul cluster ―eneadi‖, nel solo 2010, sono stati
eseguiti con successo ben 1.891 job correlati al
progetto di cui in nota, i quali hanno richiesto un tempo
totale di CPU pari a 5.703.869 secondi, corrispondenti
a 66 giorni di calcoli; il tempo medio di CPU richiesto
da questi job è stato dunque di 3.016,3 secondi, e il
valore massimo registrato è stato di 67.055 secondi.
Poiché è capitato che l‘esecuzione contemporanea di
più job eccedesse le risorse a disposizione, con la
conseguente necessità di mettere in coda uno o più job,
si è avuto un tempo totale di attesa in coda pari a ben
2.440.474 secondi, con una media di 1.290,6 secondi e
un valore massimo di 70.114 secondi, addirittura
superiore al massimo tempo di CPU impiegato dai job
del progetto.
Quanto appena detto evidenzia come, pur
limitatamente ai periodi di svolgimento dei calcoli che
riguardano determinate attività di ricerca, le risorse del
cluster ―eneadi‖ – che fino a qualche anno fa erano in
grado di soddisfare ampiamente le richieste dell‘utenza
– possano oggi rivelarsi sottodimensionate rispetto al
fabbisogno di quest‘ultima; a causa di ciò, nata
l‘esigenza di poter disporre di nuove risorse di calcolo,
si sta lavorando all‘allestimento del nuovo cluster IBM
precedentemente impiegato nell‘ambito del progetto
TriGrid.
Il cluster eneadi è formato da server che vengono
sfruttati con regolarità sia dall‘utenza scientifica che da
studenti e dottorandi di ricerca.
Nella fornitura di potenza di calcolo all'utenza va
menzionato per la sua crescente importanza il cluster
IBM (ex TriGrid). Se ne stanno rimodulando le
impostazioni (riconfigurandolo) al fine di offrire
un'equa distribuzione delle risorse, dato che tale cluster
viene già attivamente utilizzato da un gruppo di utenti.
L'alta densità di core per unità di rack disponibili, resa
possibile dall'adozione di blade IBM dotate ciascuna di
due processori Opteron dual core, consente l‘uso di un
elevato numero di core per le elaborazioni, anche di
tipo parallelo grazie all'impiego di apposite librerie.
I sistemi di calcolo scientifico messi a disposizione
del CECUM sono utilizzati anche in seguito ad una
visione allargata della ricerca. Infatti molti docenti
iniziano i loro studenti all‘uso di risorse di questo
genere nell‘ambito delle materie di cui sono titolari.
Ovviamente oltre agli studenti i due sistemi sono
pesantemente utilizzati anche dai borsisti, dai
dottorandi di ricerca, laureandi e, eventualmente, sono
stati creati account per visiting professors.
vede la partecipazione di importanti Università ed Istituzioni
di ricerca europee quali l‘Università di Manchester ed il
CNRS.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
21
ON THE WAVELENGTH SHIFT BETWEEN NEAR-FIELD PEAK
INTENSITIES AND FAR-FIELD PEAK CROSS SECTIONS IN PLASMONIC
NANOSTRUCTURES
Adriano Cacciola
Dottorato di Ricerca in Fisica dell’Università di Messina
Viale F. Stagno D’Alcontres, 98166 S. Agata-Messina, Italy
e-mail: acacciola@unime.it
Abstract
The localized plasmons of metallic nanoparticles and
nanostructures display a particular behaviour: when
they are optically excited, the near-field peak
intensities occur at larger wavelengths than the far-
field peak intensities. Here we show that the magnitude
of this shift depends on the dimensions of these
nanostructures and is theoretically predictable through
an approach based on the multipole expansion of the
electromagnetic fields within the Transition Matrix
formalism. The understanding of this phenomenon is
particularly important for Surface Enhanced Raman
Spectroscopy (SERS).
Introduction
Metal nanoparticles (MNPs) have been intensively
studied within the past decade. The unique properties
of MNPs have their applications in a broad range of
different fields, including chemistry, physics, biology,
materials science, medicine, catalysis and so on [1].
These applications rely heavily on the fact that MNPs
support localized surface plasmon resonances (LSPRs),
which are excited when incident electromagnetic
radiation creates collective coherent oscillations of the
particle free electrons [2]. Such plasmon excitations
result in a large enhancement of the electromagnetic
field around the nanoparticle, yielding both a strong
absorption and scattering of light by the nanoparticle at
the plasmon resonance frequency [3]. Varying the size
and shape of metal particles we can tune the plasmon
resonances over a wide range of wavelengths [1,2,3].
Thus, understanding the properties of plasmonic
structures of different size and shape is nowadays of
primary importance for basic and applied research as
well as for modern nano-technology [1].
Although extinction, absorption, and scattering are
still the primary optical properties of interest, other
spectroscopic techniques, e.g. SERS, are sensitive to
the electromagnetic fields at or near the particle
surfaces, thus providing important new challenges for
theory.
A well known phenomenon, that has frequently been
pointed out in the literature, is that, upon optical
excitation, the maximum near field enhancements
occur at lower energies than the maximum of the
corresponding far-field quantities [4,5,6,7]. This red
shift is known to depend on the size of the particle
[8,9], with larger particles displaying a more marked
shift. A recent systematic study has provided a
phenomenological comparison of the relationship
between the near- and far-field spectra of plasmonic
particles [10], but the physical explanation of this
apparently universal behaviour of metal particles is still
controversial. Messinger et al. [4] explain this
behaviour in terms of the radial components of the
electric field which can exist only in the near-field
zone of the sphere.
Recently Zuloaga and Nordlander [11] have
explained the physical origin of this red shift through a
mechanical analogy as a general consequence of the
behaviour of damped harmonic oscillators.
In this paper we analyze the red shift effect through
an analytical and numerical approach based on the
multipole expansion of the electromagnetic fields
within the Transition Matrix (T-Matrix) formalism
[12]. We will investigate the dependence of this red
shift upon the nanoparticle size and shape. To this aim
we start our investigation with a gold sphere and
successively we extend the description to the case of
gold dimers.
Theory
We study the optical behaviour of metal
nanoparticles, both isolated or clustered, through the
multipole expansions of the electromagnetic fields
within the T-Matrix method. This is a general
approach that applies to particles of any shape and
refractive index and for any choice of the radiation
wavelength [12]. It has been successfully applied to
several research fields, e.g. for the investigation of
interstellar dust optical properties [13,14,15], in
bioastronomy [16,17], and in optical trapping
[18,19,20,21]. Expanding the incident field in a series
of vector spherical harmonics with known amplitudes
I
p
lmW , the scattered field can be expanded on the same
basis with amplitudes '
' '
p
l mA . The relation between the
amplitudes of scattered and incident field is given by
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
22
' '
' ' ' ' I
p p p p
l m l m lm lm
plm
A S W (1)
where '
' '
p p
l m lmS is the T-Matrix of the particle[9]. The
elements of the T-Matrix are calculated in a given
frame of reference through the inversion of the matrix
of the linear system obtained by imposing the boundary
conditions to the fields across each spherical surface
[12].
The number of subunits are limited only by the
memory demand of the computing facilities. The
calculation of the T-Matrix for a N-sphere aggregate,
requires the inversion of a matrix of order d =
2N×lM(lM +2), where lM is the l-value at which the
multipole expansion of the electromagnetic fields is
truncated [12]. The choice of the value lM is carefully
checked by convergence tests ensuring the numerical
stability of the results.
The procedure devised for the extension of the T-
Matrix formalism to the study of the optical behaviour
of an aggregate of N, not necessarily equal, spheres
whose mutual distances are so small that the interaction
effects cannot be neglected can be found in [12]. In
such case the T-Matrix approach allows to take proper
account of the multiple scattering processes among the
spheres composing the aggregate.
Results
We start our investigation with a spherical gold
nanoparticle with a radius of 100 nm. The direction of
the incident field is along the z-axis and the
polarization is along the x-axis. This configuration has
been used in all our computations.
Figure 1: Scattering cross section (thick solid
line) and NFI in the forward direction (solid
line), backward direction (dotted line), and at
90° (dashed line) respect to the incident
direction for a 100 nm gold sphere. The spectra
have been normalized to their maximum values.
In Fig. 1 we compare the normalized scattering cross
section with the normalized Near Field scattered
Intensities (NFI) for three different points located at a
distance dNF from the sphere surface given by 1/10 of
the radius. This choice for dNF has been used in all the
results that we will show. All the spectra have been
normalized to their maximum values.
As is evident from the figure, the NFI is red shifted
from the far-field spectrum. This effect appears more
clearly in the backward direction and at 90° respect to
the incident direction. In the forward direction only the
quadrupole peak appears and the red shift is much
smaller.
Along the polarization direction the quadrupole peak
almost disappears and all the energy radiated by the
particle is mainly due to the dipole contribution.
Figure 2: Scattering cross sections (solid lines)
and NFI (dotted lines) for a 30 nm gold sphere
(thin lines) and for a 50 nm gold sphere (thick
lines). The spectra have been normalized to
their maximum values.
The results shown in Fig. 2 confirm, through exact
computations performed using the T-Matrix method,
the well known red shift dependence upon the
dimensions of the nanoparticle. We performed our
computations for many different particle sizes. Here,
for the sake of simplicity, we show only the scattering
cross sections and NFI for a 30 nm gold sphere and for
a 50 nm gold sphere. As the sphere size gets smaller,
the red shift reduces as well, but never disappears.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
23
In Fig. 3 we show the scattering cross section and the
NFI for a dimer made of identical gold spheres each
with a radius R=50 nm.
The dimer geometry is such that the closest distance
between the sphere surfaces is 4 nm. We computed the
NFI at the central point of the hot spot and at a distance
5 nm from the sphere surface in the external region.
We recall here that the hot spot is the region between
the spheres where the field enhancement is the highest
(see Fig. 4).
Fig. 3 clearly shows that the red shift in the hot spot
disappears, while it is still present in the dimer external
region, in analogy with the single sphere case.
Figure 3: Scattering cross section (thick solid
line) and NFI (thin lines) at the central point of
the hot spot (solid line) and at a distance d=5
nm from the sphere surface in the external
region (dotted line) for a dimer of two identical
gold spheres (R=50 nm). The spectra have been
normalized to their maximum values.
In Fig. 3 we show the scattering cross section and the
NFI for a dimer made of identical gold spheres each
with a radius R=50 nm. The dimer geometry is such
that the closest distance between the sphere surfaces is
4 nm. We computed the NFI at the central point of the
hot spot and at a distance 5 nm from the sphere surface
in the external region.
We recall here that the hot spot is the region between
the spheres where the field enhancement is the highest
(see Fig. 4). Fig. 3 clearly shows that the red shift in
the hot spot disappears, while it is still present in the
dimer external region, in analogy with the single
sphere case.
In order to demonstrate that the absence of the red-
shift in the hot spot is due to symmetry reasons, we
compute the scattering cross section and the NFI for a
dimer of gold spheres with different radii, R1=50 nm
and R2=100 nm. Also in this case the closest distance
between the surfaces of the two spheres is 4 nm (Fig.
5).
Figure 4: Near-field intensity enhancement map
for a silver dimer with R=75 nm. The closest
distance between the surfaces of the two
spheres is 5 nm.
These results show that, when we break the
symmetry of the dimer, the red shift appears also in the
hot spot. The effect appears both for the dipole and for
the quadrupole peak.
Conclusions
In conclusion, using the T-Matrix approach, we have
shown how the near-field spectra of plasmonic
nanoparticles are red-shifted compared to their far-field
spectra. In order to generalize the results and to provide
a systematic study of the relationship that exists
between far-field and near-field quantities, it is
necessary to extend the investigation to more complex
structures, like large aggregates of spheres.
We expect that taking into account the red shift
effect can provide improvement in understanding and
optimising surface-enhanced spectroscopies.
This physical insight into the behaviour of
plasmonic systems should be also useful for the
practical design of plasmonic nanoparticles and
nanostructures for applications of both fundamental
and technological interest.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
24
Figure 5: Scattering cross section (thick solid
line) and NFI (dashed lines) at the central point
of the hot spot region (solid line) for a dimer of
R1=100 nm and R2=50 nm gold spheres. The
closest distance between the surfaces of the two
spheres is 4 nm. The spectra have been
normalized to their maximum values.
Acknowledgments
I wish to thank R. Saija, M.A. Iatì, F. Borghese, P.
Denti, P.G. Gucciardi, and O.M. Maragò for fruitful
discussions and support.
References [1] S. A. Maier, Plasmonics: Fundamentals and Applications,
Springer (2007);
[2] M.L. Brongersma, P.G. Kik, Surface Plasmon Nanophotonics,
Springer Series in Optical Sciences, (2007); [3] L. Novotny and B. Hecht, Principles of Nano-Optics,
Cambridge University Press, New York (2006);
[4] B. J. Messinger el al., P. Rev. B 24 (1981) 649; [5] N. K. Grady el al., P. Chem. Phys. Lett. 399 (2004) 167;
[6] A. S. Grimault el al., Appl. Phys. B: Laser Opt. 84 (2006) 111;
[7] S. Bruzzone el al., J. Phys. Chem. B 110 (2006) 11050; [8] K. L. Kelly el al., J. Phys. Chem. B 107 (2003) 668;
[9] G. W. Bryant el al., J. Nano Lett. 8 (2008) 631;
[10] B. M. Ross el al., Opt. Lett. 34 (2009) 896; [11] J. Zuloaga and P. Nordlander, Nano Letters 11 (2011) 1280;
[12] F. Borghese, P. Denti and R. Saija, Scattering from model
nonspherical particles 2nd ed., Springer, Berlin (2007); [13] M.A. Iatì et al., MNRAS 322 (2001) 749;
[14] C. Cecchi-Pestellini, A. Cacciola et al., MNRAS 408 (2010)
535. [15] M. A. Iatì, C. Cecchi Pestellini, A. Cacciola et al., JQRST 112
(2011) 1898; [16] R. Saija et al., Astrophys. J. 633 (2005) 953;
[17] A. Cacciola et al., Astrophys. J. 701 (2009) 1426;
[18] F. Borghese et al., Phys. Rev. Lett. 100 (2008) 163903; [19] R. Saija, et al., Opt. Exp. 17 (2009) 10231;
[20] E. Messina, E. Cavallaro, A. Cacciola et al., ACS Nano 5
(2011) 905; [21] E. Messina, E. Cavallaro, A. Cacciola et al., J. Phys. Chem. C
115 (2011) 5115.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
25
MASS QUADRUPOLE SPECTROMETRY APPLIED TO LASER-
PRODUCED PLASMAS AND MICROWAVE IGNITED PLASMAS
F. Di Bartoloa, *, L. Torrisi
b,c, S. Gammino
c , F. Caridi
d, D. Mascali
c,e, G. Castro
c,f , L. Celona
c,
R. Miracolic,f
, D. Lanaiac, R. Di Giugno
c,f.
a) Dottorato in Fisica dell’Università di Messina, Dip.to di Fisica, V.le F. Stagno D’Alcontres 31, 98166, S. Agata-
Messina, Italy
b) Università degli Studi di Messina, Dip.to di Fisica, V.le F. Stagno D’Alcontres 31, 98166, S.Agata-Messina, Italy
c) INFN - Laboratori Nazionali del Sud, via S.Sofia 62, 95123 ,Catania, Italy
d) Università degli Studi di Messina, Facoltà di Scienze MM.FF.NN., V.le F. Stagno D’Alcontres 31, 98166, S. Agata-
Messina, Italy
e) CSFNSM, Viale A. Doria 6, 95125 Catania, Italy
f) Università degli Studi di Catania, Dipartimento di Fisica e Astronomia, V. S.Sofia 64, 95123 Catania, Italy
* Corresponding author, e-mail: fdibartolo@unime.it
Abstract
The mass quadrupole spectrometry (MQS) permits
the characterization of non-equilibrium and
equilibrium plasmas obtained by means of laser
ablation and microwave ionization. A Nd:Yag laser,
150 mJ pulse energy, 3 ns pulse duration, operating at
1064 nm fundamental and 532 nm second harmonic
wavelength, at intensities of the order of 1010 W/cm2,
in single pulse or at a repetition rate between 1 and 10
Hz, interacting with solid targets placed in high
vacuum produces ablation with plasma formation. It is
possible to analyze the ion and the neutral emission
from plasma in the mass range 1-300 amu with a mass
resolution better than 1 amu and a sensitivity of the
order of 1 p.p.m.. Moreover, it is possible to select the
ion energy in the range 1 eV – 1 KeV with an electric
deflection filter.
MQS allows to measure the temperature and density
of the plasma, the relative ion and neutral amounts, the
fractional ionization of the plasma, the elements and
chemical compounds of the species participant to the
plasma formation, the ion charge state, the ion energy
distributions and the angular distribution of the emitted
ions. Operating in repetition rate it measures the depth
profile of peculiar elements in the ablated targets.
Moreover, MQS permits also to characterize
microwave ignited plasmas, obtained by means of
microwaves at two different frequencies, 2.45 GHz
(Magnetron) and 3.7478 GHz (TWT), axially launched
inside the plasma chamber, where a strongly non
uniform magnetostatic field exists (with a maximum
value of 0.1 T), with two possible configurations
depending on the used ion source (Plasma Reactor or
VIS). In the regions under ECR (Electron Cyclotron
Resonance) the X-B conversion is possible, the
incoming electromagnetic extraordinary mode X is
converted into a Bernstein wave B, i.e. an electrostatic
wave which can propagate in an overdense plasma.
Plasma density and temperature measurements,
obtained with a Langmuir Probe and X-ray detectors,
confirmed successfully the mode conversion and the
formation of an overdense plasma.
The similarities with non-equilibrium plasmas
generated by laser ablation will be described along
with the differences.
Keywords: Mass Quadrupole Spectrometry, Laser-
Plasma, Electrostatic Bernstein Waves, Plasma heating,
Plasma vortex
Introduction
Mass spectrometry (MS) is an analytical technique to
measure the mass-to-charge ratio of charged particles
(m/q).
A mass spectrometer is used to determine elemental
composition, compounds and isotopes and, if there is
also an energy filter, ion and neutral energy
distributions. It permits to analyze both ions and
neutrals, and is made up of three main parts: an internal
ionization source, a mass analyzer and a detector [1].
It is known that intense pulsed laser beams, with an
intensity of 1010
W/cm2, can be focused on a solid
material to produce ablation and formation of hot non-
equilibrium plasmas, which have a duration of a few
nanoseconds. The processes developed inside the laser-
generated plasma depend on many parameters, such as
the laser characteristics, lens focalization, target
composition, irradiation conditions, etc..
PLA obtained with ns lasers at high intensity
generates hot plasma at the target surface, which
expands in vacuum at supersonic velocity mainly along
the normal to the irradiated target surface. A plasma
characterization, in terms of temperature, density,
energy of ejected particles, fractional ionization and
charge state distribution, necessary to differentiate the
plasma laser production, can be obtained.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
26
Equilibrium plasmas are generated by means a
Microwave Discharge Ion Source (MDIS), usually
used to produce high intensity proton beams (above 50
mA). The operations of these devices is essentially
based on the so called off-resonance discharge in a
quasi-constant magnetic field B~0.1 T, obtained by
launching microwaves with f= 2.45 GHz or 3.7478
GHz inside a metallic cavity of few cm of length and
diameter. Such devices are density limited if the ECR
is the only heating mechanism: the electromagnetic
waves cannot propagate over a certain density, called
cut-off density. To overcome the density limitations
electrostatic Bernstein waves (EBW) heating [2] is an
option. The EBWs are able to propagate in largely
overdense plasmas, i.e. plasmas above the cut-off (ncut-
off=3x1010
cm-3
), being absorbed at cyclotron harmonics
[3]. EBW are created inside the plasma when a X
wave, i.e. an extraordinary, E.M. wave, is converted
from an E.M wave. It can be shown that X waves
convert into EBW and ion waves at Upper Hybrid
Resonance, when 2 2RF P C P being the
plasma frequency and 2C being the cyclotronic
frequency.
Material and methods
A Q-switched Nd:Yag pulsed laser operating at 1064
nm fundamental wavelength and at 532 nm second-
harmonic wavelength, with 3 ns pulse duration and 160
mJ maximum pulse energy, in single shot and
repetition rate (1 and 10 Hz) mode, was employed for
the measurements.
The laser beam was focused, through a 50 cm focal
lens placed in air, on the surface of a SiO2 target, on
which it produces a 0.5 mm2 spot size, the laser-target
interaction occurs inside a vacuum chamber, at 5 x 10-6
mbar pressure, and leads to the plasma formation. Ions
and neutral particles are analysed by the MQS.
Two types of mass quadrupole spectrometer have
been employed:
1) a classical version of MQS, a Pfeiffer Vacuum
Prisma Plus QMG 220, Mass Range 1-300 amu, Mass
resolution < 0.3 %, Sensitivity (SEM) 1 ppm;
2) a special electrostatic mass quadrupole
spectrometer with an energy filter, Hiden EQP 300,
Mass range 1-300 amu, energy range 1 eV-1 keV,
Sensitivity 1 ppm.
The second type of mass spectrometer, differently
with respect a classical MQS, permits to plot the
energy distribution of neutral and charged species in
the energy range 1 eV – 1 keV. Figure 1 shows the
experimental set-up (a) and the scheme of the Hiden
EQP instrument (b). EQP is placed at 45º with respect
to the incidence laser beam, i.e. along the normal to the
target surface [4].
We also used Cu, Al and Ta targets for our
measurements.
EQP spectra were analysed in order to determine the
Cu ion energy distribution and separate the neutral
component from the ionic component for Al and Ta
targets. The fits of the experimental energy
distributions were performed by means the ‗‗Peakfit‖
numerical code using the ―Coulomb-Boltzmann
shifted‖ function:
(0.)
3
2
1( )
2 ( )
1exp ( )k C
Af E E
m kT
E E EkT
(1)
Fig.1 Scheme of the EQP instrument (a) and
photo of the experimental set-up (b)
Vacuum chamber
Laser system
MQS
b)
a)
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
27
The characterization of equilibrium plasmas has
been done by means a MDIS called VIS (Versatile Ion
Source). The source body consists of a water-cooled
copper plasma chamber (100 mm long and 90 mm
diameter). VIS enable us to have purely off-resonance
microwave injection (which is not possible using
Plasma Reactor, another MDIS with a slightly different
magnetic profile). Microwaves have been generated by
using a conventional 300 W magnetron, able to
generate 2.45 GHz microwaves, or a Travelling Wave
Tube (TWT), able the generate microwaves from 3.2 to
4.9 GHz. The typical working frequency when using
TWT was 3.7478 GHz. The measurements of
temperature and plasma density have been carried out
by using a movable Langmuir probe (LP). A Si-Pin X-
ray detector has been used for the measurement of X
rays spectra in different plasma conditions. The
detector is able to detect X rays with energy greater
than about 1 keV.
Results and discussions
A. PLASMA LASER ABLATION (PLA)
MQS can operate versus mass and versus time. In
the first case we have a mass spectrum, where each of
the detected peaks corresponds to a certain element or
chemical compound. In the second case we obtain a
MQS time spectrum, for some selected masses, which
allows to know the relative elemental concentrations
vs. the ablation time, permitting to plot the element
depth profiles. The mass quadrupole spectrometer
must be calibrated to know the exact number of atoms
or molecules of the target detected during the laser
ablation. In Figure 2 (a) the apparatus for the MQS
calibration is shown [5,6]. In our calibration test, we
employed a mixture of gas (50% Helium and 50%
Argon) enclosed in a volume V0 = 55.8 cm3. The initial
and final pressure of the gas in this volume are Pi and
Pf, respectively, at a room temperature T = 22ºC.
After that we open the Valve 3 in order to introduce
a known gas quantity in the vacuum chamber, very
near to the target position. We introduce a molecular
number N = 0.668 x 1020
of Argon and Helium atoms
into the vacuum chamber.
The calibration spectrum obtained by using the MQS
permits to calculate the yield of Ar corresponding to 84
C. Afterwards we obtain the target spectrum which
permitted us to calculate the yield of Si corresponding
to 0.04 C. Calculating the ablation yield is possible by
means the following proportion
: Ar = Y : Ar SiY atoms X atoms Si
(2)
Fig.2 Scheme of the gas calibration apparatus.
Thus the ablation yield resulted 3.18 x 1016
atoms of
Si ablated for laser pulse.
EQP Mass Spectrometer permits to obtain the ion
energy distribution for a Cu target at two different laser
energies, 40 mJ and 160 mJ, respectively. In the first
spectrum the peak energy is 3eV while in the second
one the peak energy is 17 eV. In figure 3 spectra
obtained at energy of 160 mJ are shown.
Making a fit with a ―Coulomb-Boltzmann shifted‖
function we can know two important parameters of a
plasma, the temperature KT and the acceleration
voltage V0. The temperature is 2.9 eV and 8.9 eV,
respectively.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
28
Fig. 3 Ion energy distribution and fit for a Cu
target at a laser energy of 160 mJ.
Assuming the peak energy to be representative of the
distribution mean energy, we find that the mean energy
for the only ions is higher with respect to the spectrum
obtained detecting ions plus neutrals. At 150 mJ the
neutral plus ion mean energy is 85 eV and 115 eV for
Al and Ta, respectively. At 150 mJ the only ion mean
energy is 95 eV and 120 eV for the two cases,
respectively. Thus ions have mean energy higher with
respect to neutral specie.
The ‗‗Peakfit‖ deconvolution process applied to the
ions plus neutral spectra separates the two components,
ions from neutrals, and permits to extrapolate the
neutral energy distribution by the difference between
the ions plus neutral spectrum and the only ion
spectrum. Fig. 4 shows the deconvolution spectrum
obtained from an aluminium target. Deconvolution
spectra report the neutral energy distribution
(continuum line) obtained subtracting the only ion
spectrum (full dots) to the ion plus neutral spectrum
(open dots). The energy distributions of the neutral
specie, obtained irradiating at 150 mJ pulse energy,
show mean energies, E , of about 60 eV and 65 eV for
Al and Ta ablation, respectively. These energies are
representative of the plasma temperature through the
following relationship:
( ) 2 ( ) / 3kT eV E eV (3)
where k is the Boltzmann constant. Eq. (2) gives 40
eV and 43.3 eV for Al and Ta neutral temperature,
respectively.
Ions are characterized by energy higher with respect
to the neutrals, due not only to the thermal interactions
between the plasma particles and to the adiabatic gas
expansion in vacuum but also to the Coulomb
interactions between the charged species. [7]
Fig.3 Ion energy distribution and fit for a Cu target at
a laser energy of 160 mJ.
B. PLASMAS MICROWAVES-GENERATED
In the measurements performed with plasmas in
equilibrium, we modified the position of the magnetic
field with respect to the plasma chamber of VIS; in
such a way, microwave injection takes place at
different values of magnetic field. In figure 5 are
shown. We use as reference BECR. X ray were detected
particularly in position D (Binj/BECR=0.92, 1 keV
spectral temperature). When the injection approaches
Fig.4 Deconvolution spectrum reporting the
neutral energy distribution (line) obtained
subtracting to the only ion spectrum (fill dots)
the ion plus neutral spectrum (open dots) for Al
ablation.
BECR, X rays tend to disappear and finally, at
position A (Binj/BECR>1), no X rays were detected.
These results show that the production of high energy
X rays (T>1 keV) takes place only in case of under-
resonance discharge, that is the required condition to
have UHR placed somewhere inside the plasma.
Emittance measurements carried out in configuration A
and in configuration D have shown a larger emittance
in configuration D (0.207 πmm mrad) than in
configuration A (only 0.125 πmm mrad). The
emittance depends by the magnetic field at
A
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
29
extraction Bext, the radius of extraction r , the ratio of
ion mass in amu to charge state of the ion beam M/Q
and the root square of ionic temperature [8,9].
2 10.016 0.032
/ /
iext
kTr r B
M Q M Q (4)
In our magnetic configurations emittance only
depends on iT . Ionic waves are absorbed by ions
through Landau damping. If Ti are high we have a
large emittance, therefore the more intense beam
permitted by EBWs will be balanced and the
brightness, that is the current intensity-emittance ratio,
will not change and the ion source will not efficient. If
Ti are low we have an high current intensity, due to
high density possible with EBWs, a low emittance and
therefore an high brightness: the ion source will be
efficient. However if Ti are very high, in fact, value of
10 keV are possible due to the generation of vortex
inside the plasma, we will get auto-accelerated ions,
considering that in a common ion source ions have
energy of eV or a fraction of eV [10].
Conclusions
The mass quadrupole analyser measures the mass-to-
charge ratio (m/z) of the ions produced.
A mass quadrupole spectrometer allows to determine
main plasma parameters as the plasma temperature
(KT), density (n), fractional ionization (f=ni/nt),
acceleration voltage (V0) and electric field (E) [10].
EQP demonstrated high versatility to investigate on the
amount and energy distribution of neutrals and allows
to measure the plasma temperature starting directly
from the neutral energy distribution. We will be
performing measurements with the Mass Quadrupole
Spectrometer Hiden EQP 300 to determine ions energy
inside an equilibrium plasma in which a EBWs-heating
mechanism occurs. In such a way we will compare ions
energy obtained in non-equilibrium plasmas with that
ones obtained in equilibrium plasmas to understand if
EBW-heating mechanism allows to have an efficient
ion source or high-energy autoaccelerated ions.
Fig. 5 Position of Microwave injection with
respect to off-resonance, in configuration B, C
and D the injection occurs under-resonance (a);
X ray detected at different position of magnetic
field (b).
References [1] E. De Hoffmann and V. Stroobant, Mass Spectrometry: Principles and
Applications, 3rd ed.Wiley (2007). [2] Ira B. Bernstein., Phys. Rev.,
109, (1958) 10;
[2] Ira B. Bernstein., Phys. Rev., 109, (1958) 10;
[3] K. S. Golovanivsky et al., Phys. Rev. E 52, (1995) 2969;
[4] L. Torrisi et al., NIM B266 (2008) 308;
[5] L Torrisi. et al. Rad. Eff. and Def. in Solids, 161(1) (2006) 3-13.
[6] F. Di Bartolo et al. Nucleonika (2011), submitted
[7] L . Torrisi et al. , Appl. Surf. Sc., 252 (2006) 6383;
[8] D. Mascali et al., NIM A, 653 (2011) 11;
[9] G. Castro et al., ICIS ‘11, Rev. Sc. Instr., (2011), in press;
[10] K. Nagaoka et al., Phys. Rev. Lett.89 (1992) 7.
-20 -10 0 10 20700
800
900
1000
1100
1200
Position [mm]
B [G
]
Magnetic field [G]
ECR = 875 G
D C B A
a)
b)
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
31
FUSION REACTIONS IN COLLISIONS INDUCED BY LI ISOTOPES ON SN
TARGETS
M. Fisichellaa,b
, A. Di Pietrob, A. Shotter
c,d, P. Figuera
b, M. Lattuada
b,e, C.Marchetta
b, A.Musumarra
b,e, M.G.
Pellegritib,e
, C.Ruizc, V. Scuderi
b,e, E.Strano
b,e, D.Torresi
b,e, M.Zadro
f
a)Dipartimento di Fisica, Università di Messina, Messina, Italy
b)INFN- Laboratori Nazionali del Sud and sezione di Catania, Catania, Italy
c)TRIUMF, Vancouver, Canada
d)School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK
e)Dipartimento di Fisica ed Astronomia, Università di Catania, Catania, Italy
f)Ruđer Boŝković Institute, Zagreb, Croatia
Abstract
For investigating the role of the Q-value for neutron
reaction in fusion reaction induced by weakly bound
nuclei, fusion reactions of lithium isotopes with a
combination of different Sn isotopes have been proposed,
by using an activation technique. 6Li+
120Sn and
7Li+
119Sn
have been already performed. I will show here the result
of the preliminary analysis of these two reactions.
Introduction
Recently more and more experimental evidences have
been observed concerning the enhancement of the sub-
barrier fusion cross section due to neutron transfer, both
in reaction with stable nuclei [1,2] and especially in
reaction with weakly bound nuclei[3]. In particular the
enhancement seems to be related to sign of the Q-value
for neutron transfer. A new mechanism has been proposed
[4] for the sub-barrier fusion of weakly bound nuclei, in
which an intermediate rearrangement of valence neutrons
with positive Q-value may lead to a gain in kinetic energy
of the colliding nuclei and, thus, to enhancement of the
barrier penetrability and therefore of the fusion cross-
section. To investigate the role played by the coupling to
transfer channels having positive Q-value, we have
proposed to study the fusion of lithium isotopes with a
combination of different Sn isotopes. The systems which
would like to study are 6Li+
120Sn,
7Li+
119Sn,
8Li+
118Sn
and 9Li+
117Sn. All these reactions lead to the same
compound nucleus but are characterized by different Q-
value for neutron transfer. The fusion cross section are
measured by using an activation technique where the
radioactive evaporation residues produced in the reaction
are identified by the X-ray emission which follows their
electron capture decay.
The 6Li+
120Sn,
7Li+
119Sn have been already performed at
LNS, Catania. The 8Li+
118Sn,
9Li+
117Sn will be performed
at TRIUMF, Canada.
Experimental technique
As in our previous experiment [5,6], we proposed to
measure the fusion excitation function by using an
activation technique, based on the off-line measurement
of the atomic X-ray emission following the electron
capture decay of the evaporation residues produced in the
reactions.
The direct detection of E.R., produced in the collision of a
low energy light projectile onto a medium target is not
possible since the largest fraction of E.R. produced will
not come out from the target owing to the their low
kinetic energy. But by choosing a suitable target, with the
help of statistical model calculation, it is possible to
obtain E.R. unstable against E.C. decay and so it is
possible to identify the E.R. by looking at their X rays.
This technique consists of two steps: the activation of the
target and the off-line X-ray measurement.
The activation step of the measure has been performed in
the CT2000 scattering chamber at LNS with the 6Li and
7Li beams delivered by the SMP Tandem Van Graaff
accelerator. A stack of four Sn targets followed by Nb
catchers were irradiated with the Li beam. The catchers
were needed in order to stop the residues emerging from
the previous target and to slow down the beam, thus
increasing the average difference in beam energy for the
different targets. Possible reactions induced by the beam
on the 93
Nb catchers do not represent a problem since the
X-ray energies are different to the ones corresponding to
reactions on 64
Zn. By activating a stack of targets it is
possible to extract the cross section at different energies
without changing the beam energy thus reducing the
beam time needed to perform an excitation function
measurement with the very low intensity radioactive
beams. This technique is for this reason very useful in the
case of radioactive beam.
Two irradiation runs are been performed for each system:
1) A first stack was irradiated with 25 MeV 6,7
Li beam
of about 1010
pps for about three hours.
2) A second stack was irradiated for about three days
(to optimize the 124
I production at low energy) with 21
MeV 6,7
Li beam.
By using these stacks, a centre of mass energy range
between 16 MeV< Ec.m. < 24 MeV .To extract the
production cross section it is necessary to measure the
beam current as a function of time for the entire duration
of the activation step. This operation has been performed
using two Surface Barrier Silicon Detector collecting the
particles scattered by a thin gold foil placed before the
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
32
stack on the beam line. Since the scattering is of
Rutherford type, the beam intensity can be extracted by
his well-known cross-section formula. With the two
symmetrical monitors it is possible to reduce systematic
errors due to mechanical misalignments. After the
irradiation, the E.R. emitted from the different targets
(together with the corresponding catcher) were measured
off-line using Pb shielded large area Si(Li) detectors.
Each measurement was repeated in order to measure the
activity as a function of time. For determining the fusion
cross section it is really important to know the intrinsic
efficiency of the detector. We measured the efficiency of
our detector using some calibrated sources, because in the
energy range, in which we are interested in, the efficiency
for these detector is strongly dependent from the energy.
PRELIMINARY RESULTS
Typical X-ray spectra measured off-line for the reaction 6Li+
120Sn is shown in figure 1, where the peaks
corresponding to Kα and Kβ X-ray emission of Sb and I
are shown. The Kβ emission represents about 15% of the
total k X-rays emission. In the present experiment, the
analysis was performed only on the Kα lines.
Figure 1 Typical X-ray spectra measured off-line
for the reaction 6Li+
120 Sn at 25 MeV. It is possible
to distinguish Sb and I peaks.
From the X-ray energies we can only identify different
elements but not different isotopes. We can characterize
the isotope by following the time behavior of the X-ray
lines, characteristic of each element, and by fitting it
using the known half-lives. Plotting these data on a semi-
logarithm graph (that is ln A vs t) should give a straight
line of slope -λ, the decay constant .In figure 2 a typical
activation curve for the reaction 6Li+
120 Sn at 25 MeV is
shown. It is possible to observed three different slope
which characterize this curve. Each slope correspond to a
different I isotope produced in the reactions. In particular
one may observe the contribution of 123,124,125
I.
Figure 2 Activity curve for the I isotopes, obtained
for the reaction 6Li+
120 Sn at 25 MeV.
By fitting the activation curves for each E.R. one
obtains the A0exp, that is its activity at the end of the
irradiation time, which is another important quantity for
the measurement of the fusion cross section.
Future perspectives
The fusion cross section is given by the following
relation:
0exp
0i t T
A
N N K (1)
where 0exp 0A represent the number of compound
nuclei at the end of the irradiation time. As it was told
before, 0expA is obtained from the fit of the activation
curve (figure 2).
The term is then corrected for the fluorescence
probability ( K ) and for the detector efficiency ( T ),
which is determined experimentally by using calibrated
sources. tN is the number of target atom per cm2 and tN
is the incident beam current (i.e. the number of incident
particles), which is determined by analyzing the
Rutheford scattering data. The next step of my analysis
will be just the determination of iN , and then the
measurement of the fusion cross section for the two
reaction already performed. From the comparison of the
fusion cross sections of all the systems it will be possible
to investigate on the possible role of the Q-value for
neutron transfer in the fusion reaction.
References
[1] Trotta et al., Phys.Rev. C 65, 011601(2002);
[2] Stefanini et al, Phys.Rev. C 74 034606 (2006);
[3] Penionzhkevich et al., Phys. Rev. Lett. 96 162701(2006);
[4] Zagrebaev et al., Phys. Rev. C 67 061601(R) (2003);
[5] Di Pietro et al. Phys.Rev.C 69 (2004) 044613;
[6] Di Pietro et al. Europhys.Lett. 64 (2003) 309.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
33
PARTICLE CORRELATIONS AT INTERMEDIATE ENERGIES AND THE
FARCOS PROJECT
T. Minniti1,2
and Farcos/Chimera collaboration
1Dipart. di Fisica, Università di Messina, v.le F. D’Alcontres 31, 98166 S. Agata, Messina, Italy.
2INFN-Gruppo collegato di Messina, Messina, Italy.
Corresponding Author: tminniti@unime.it
Keywords: Particle correlations, correlation functions.
Abstract
The study of correlations between two or more
particles emitted during a nuclear reaction provides
tools to explore the space-time properties of the
reaction and spectroscopic features of produced exotic
clusters [1]. Correlation imaging techniques are known
to provide ―space-time‖ snapshots of particle emitting
sources [1]. These sources allow one to extract the size
of emission regions in properties of nuclear matter
produced during the reaction. Moreover, two-nucleon
correlations probe the relative emission times of pre-
equilibrium protons and neutrons that are strongly
affected by the symmetry energy and its symmetry
dependence [2]. Studies with particle correlators used
in heavy-ion collision experiments conducted at MSU
and at the LNS will be presented and discussed. Future
improvements of these studies require a new array of
telescopes with high angular and energy resolution
coupled to a 4 detector necessary to perform better
exclusive measurements. In order to address these
topics a new project has been started at the INFN,
Sezione di Catania and Laboratori Nazionali del Sud.
The name of this project is FARCOS (Femtoscope
ARray for COrrelations and Spectroscopy) and it
consists of building an array of double-side silicon strip
detectors and CsI(Tl) crystals characterized by high
angular and energy resolution. Farcos will represent an
important scientific upgrade of the physics studies with
the Chimera detector at INFN. The array can be used
as a correlator to be coupled to existing 4 detectors
such as Chimera at LNS. Such as 4 device is
necessary to characterize the collision events
(determination of impact parameter, reaction plane,
fragment yields and spectra) while Farcos is used in
coincidence to measure correlation functions. The
Farcos array will be characterized by a compact
electronics and a geometric flexibility that will also
allow it to be transported to different laboratories,
depending of the beam/target combination to be
studied, that to be adapted to different 4 detector
environments (Chimera at the LNS, Indra at GANIL,
etc.). These features and their impact in future
programs of Farcos+Chimera experiments at the LNS
of Catania will be described. These will involve
experiments to study decay channels of unbound and
exotic nuclei produced in both direct reactions with
radioactive beams and with heavy-ion collisions at the
LNS of Catania [3,4]. In the second case, several
unbound states are indeed produced during the
dynamical evolution of heavy-ion collisions and one
can study some spectroscopic properties such as their
sequential decays proceeding through the production of
sequences of unbound nuclei or cluster and nuclear
molecular states [4].
Introduction
The study of correlations between particles emitted
during a collision between two heavy ions provides
information about the space-time properties and
quantitative understanding of reaction dynamics. This
in turn depends on the details of the nuclear interaction
and the equation of state (EoS) of nuclear matter. The
future radioactive beam facilities as well as the existing
stable beam laboratories will allow studying these
problems with higher sensitivity to the isospin degree
of freedom thanks to the capability of accelerating
highly N/Z asymmetric beams at intermediate energies.
In this respect, detectors capable of detecting all
reaction products on an event-by-event basis and
measure their reciprocal correlations are mandatory
[1,2]. Different observables need to be measured over a
large solid angle coverage with high energy and
angular resolution. The solid angle coverage
guarantees a characterization of the collision event.
The energy and angle resolution are important in order
to measure the momentum vectors and kinetic energies
of the detected particles and explore their correlations.
Recent implementation of pulse-shape identification
techniques promise to provide unique capabilities [3-5]
that will allow studying nuclear dynamics even at low
energies at facilities such as Spiral2 and Spes [6].
In this contribution we present the physics cases for
the construction of a detector array meant to measure
correlations between particles and fragments in
coincidence with large solid angle arrays. The name of
the project is Farcos, standing for Femtoscope ARray
for Correlations and Spectroscopy. It is expected to
address topics in ―femtoscopy‖ via intensity
interferometry and spectroscopy with radioactive
beams.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
34
Dynamics and two-particle correlations
Heavy-ion collisions allow one to explore the
properties of nuclear matter under extreme conditions.
A clear understanding of the dynamics of heavy-ion
collisions is required. Particles are emitted at different
stages that are difficult to isolate. It is therefore
important to disentangle particle and fragment emitting
sources. Where and when are fragments produced?
Understanding dynamics in heavy-ion collisions
requires tracing-back particle and fragment emitting
sources. Such challenge can be accomplished by using
two-particle correlation function known to be sensitive
to the space-time features of nuclear reaction
mechanisms [7]. The shape of correlation functions
probe important transport properties of nuclear matter
and the density dependence of symmetry energy in the
equation of state.
Figure 1. Left panel: Two-proton correlation
functions measured in Ne+Au collisions at
E/A=75 MeV. See Ref. [8] for details. Right
panel: emitting source functions extracted by
imaging.
Two-proton correlation functions, 1 ( )R q , is
defined as the ratio between the two-proton
coincidence and uncorrelated spectra, ( )coinY q and
( )uncoY q , respectively. q is the relative momentum
between two protons in coinY and uncoY spectra.
Uncorrelated proton pairs are usually constructed by
coupling protons from different events. Fig. 1 shows
such a correlation function in the case of N+Au
collisions at E/A=75 MeV [8]. The peak at q=20
MeV/c is due to the nuclear interaction between the
two protons and determines the spatial extent of the
emitting source, S(r), defined as the probability of
emitting two protons with a relative distance r recorded
at the time when the second proton is emitted. Imaging
techniques [8 and Refs. therein] have been successfully
used to extract the emitting source function from the
measured correlation function. This images represent
sort of ―space-time pictures‖ of the emission [7-9]. The
right panel of Fig. 1 shows the source functions, S(r),
extracted from the correlations represented on the left
panel. The source function not only provides
information about the size/volume of the emitting
source, but also allows us to estimate the relative
contributions between fast dynamical pre-equilibrium
sources and slowly evaporating sources characterizing
the later thermalized stages of the reaction [8]. This
sensitivity of R(q) to the space-time features of the
reaction becomes very useful as tool to explore
transport properties of nuclear matter. Indeed
microscopic transport models have shown sensitivity to
the nucleon-nucleon (NN) collision cross section in the
nuclear medium [9] and to the density dependence of
the symmetry energy [10]. Such research program
requires also the difficult task of measuring p-p, n-p
and n-n correlation functions in the same experiment
[10]. Coupling charged particle and neutron detectors
is also a priority in this respect.
Extending these measurements to fragment-fragment
correlation functions allows one to extract space-time
information about the stage of heavy-ion collisions
when nuclear matter at low density breaks-up into
complex fragments possibly indicating the occurrence
of a phase-transition [11] and carrying important
signatures of the effects of the symmetry energy and its
density dependence. The possibility of measuring
fragment correlation functions is further enriched by
the introduction of powerful pulse-shape capabilities
that would allow identifying fragments at low kinetic
energies [3,4]. These fragments can be identified only
by a detailed study of the shape of the signal induced
by their passage through the detector [2-4]. Another
important application of intensity interferometry is
represented by the study of correlations between unlike
light particles, such as proton-alpha, deuteron-alpha,
deuteron-3He, etc. [7]. An extended study of all these
correlation functions would allow a reconstruction of
several emitting sources in the same reaction. These
light particle correlations are usually characterized by
the presence of several resonances and a precise
measurement of their position and shape is mandatory
in order to probe their emitting sources. High angular
resolution is thus a key feature of an array meant to
perform correlation measurements between light
particles.
Correlation functions as a spectroscopic tool
During the dynamical evolution of the system
several loosely bound nuclear species are produced for
a very short time and decay. Their unstable states can
be identified and explored by detecting all the products
of their decay in coincidence. A typical example of this
type of analyses has been shown in Ref. [12] where p-7Be correlation functions were measured in order to
study unbound states in 8B nuclei and probe their spins
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
35
[12]. In a more recent experiment, three- and four-
particle correlation functions have been used to study
highly lying unbound states in 12
C and 10
C nuclei [13].
Three-alpha particle correlation functions can be used
to study the decay of internal states in 12
C. While two-
alpha-two-proton correlation functions probe 10
C
decay. In the case of 12
C these correlation studies allow
one to disentangle the direct decay into three alpha
particles from the sequential decay into 8Be+alpha with
a subsequent decay of 8Be into two alphas. In the case
of 10
C studies one can identify the decay sequence of
unbound states that produce intermediate states in 6Be,
8Be and
9B [13]. The techniques reported on Ref. [13]
show that one single heavy-ion collision can provide
access to some spectroscopic information of exotic
unbound states. The availability of very proton-rich
beams at the future exotic beam facilities can enhance
the possibility of producing even more exotic
resonances and study their decay properties.
Figure 2. Left panel: Schematic view of the
expected design of Farcos telescopes. Right
panel: Coupling of the Farcos array to the
Chimera detector at the LNS of Catania.
Required array features
Based on the physics cases outlined above, we plan
to build an array of silicon strip and CsI(Tl) telescopes
to be coupled to large detector arrays such as
Chimera@LNS-Catania. A minimum of about 15
telescopes is required in order to address a number of
physics cases as outlined above. However a larger solid
angle coverage would significantly increase the
scientific reach of the project. The array will have a
large geometric flexibility. Silicon strip detectors with
thicknesses of 300 and 1500 m (6.4 x 6.4 cm2) will be
followed by 6 cm –long CsI(Tl) crystals arranged in a
square configuration 2 x 2 (each crystal will have a
front face of 3.2 x 3.2 cm2). This array will provide an
angular resolution up to about 0.1o at a distance of 1 m
from the target. The left-end side of Fig. 2 shows a
schematic view of the basic telescope. The geometry
flexibility of the telescopes is expected to allow the use
of an additional silicon strip detector aimed at lowering
the identification threshold. Low thresholds will also
be attained with pulse-shaping techniques [3-5].
Silicon nTD solutions are also under consideration to
improve pulse-shaping capabilities. The required
electronics will need to address the goal of obtaining
high resolution, high dynamic ranges and high
flexibility (programmability) in order to identify light
and heavy fragments. Due to the large number of
channels that will be employed in the array, an
integrated electronics solution will be required. The
right-end side of Fig. 2 shows a possible arrangement
of the array inside the Chimera reaction chamber at the
LNS of Catania. The use of the array in studying
correlations between charged particles and neutrons is
also envisioned and will require a specific study on the
materials required in order to couple Farcos telescopes
to neutron counters.
The high flexibility of the array will certainly allow
further applications at the future radioactive beam
facilities, especially when studying reactions induced
by proton-rich beams. These beams will allow studying
correlations between charged particles emitted by
short-lived exotic nuclei abundantly produced close to
the proton-drip line (two- and multi-proton emitters,
etc.). Also, studying direct reactions induced by
radioactive beams, such as (p,d), (d,p) etc. reactions,
will be possible due to the envisioned high energy and
angular resolution and to the geometric flexibility [14].
References 1. J. Pouthas et al., Nucl. Instr. and Meth. A 357 (1995) 418;
2. A. Pagano et al., Nucl. Phys. A681 (2001) 331c; 3. A. Alderighi et al., IEEE Trans. on Nucl. Sci. 52, (2005) 1624;
4. L. Bardelli et al., Nucl. Instr. Meth. A 605 (2009) 353;
5. L. S. Barlini et al., Nucl. Instr. Meth. A 600 (2009) 644; 6. http://www.ganil-spiral2.eu; http://www.lnl.infn.it/~spesweb;
7. G. Verde et al., Eur. Phys. J. A 30 (2006) 81; 8. G. Verde et al., Phys. Rev. C 65, 054609 (2002);
9. G. Verde et al., Phys. Rev. C 67, 034606 (2003);
10. L.W. Chen et al., Phys. Rev. Lett. 90, 162701 (2003); 11. L. Beaulieu et al., Phys. Rev. Lett. 84, 5791 (2000);
12. W.P. Tan et al., Phys. Rev. C 69, 061304 (2004);
13. F. Grenier et al., Nucl. Phys. A 811, 233 (2008) ; 14. E. Pollacco et al., Eur. Phys. J. A 25, s01, 287–288 (2005).
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
37
INVESTIGATION ON PSEUDOSCALAR MESON PHOTOPRODUCTION
BY ELECTROMAGNETIC PROBE
M. Romaniuka,b,c,*
, V. De Leoa,b
, F. Curciarelloa,b
, G. Mandaglioa,b
, G. Giardinaa,b
a) Dipartimento di Fisica, Università di Messina, I-98166, Messina, Italy
b) INFN- Sezione Catania, I-95123, Catania, Italy
c) Institute for nuclear Research, National Accademy of Science of Ukraine, Kiev, 03680, Ukraine
* e-mail: mromaniuk@unime.it
Abstract
The Dalitz decay, second most common decay mode of 0 e e , with probability 0.01198, was
studied. Dalitz and double Dalitz decays are of interest
because they can be exploited to perform a
measurement of the electromagnetic form factor of the
decaying meson. Such mode of pions decay is a
prominent quantity in many sub-fields of particle
physics, such as chiral perturbation theory and for g-2
physics. Performed analysis of the GRAAL data and
prospective for BGO-OD for interested channel.
Introduction
The studding of the nucleon structure is one of
primary interests in the strong interaction physics and
has been the subject of experimental and theoretical
studies for several decades. To describe strong
interactions we are using Quantum Chromo Dynamics
(QCD) – the formal theory of the colour interactions
between quarks. In the high energy regime (αs<<1)
common tool to perform investigation at QCD is
perturbative approach. In low energy regime( where
αs≈1), which is typical of the nucleon and its
resonances, it is not possible to use perturbative
approach. Using different effective degrees of freedom
of the nucleon one could obtain different nucleon
resonance spectra. But up to now exist an open
problem with missing resonances: not all predicted
states was observed. The dominant decay channel for
nucleon resonances is the strong decay with single or
multi meson emission.
The excited states have strong overlapping between
the excitation curves of resonances whose masses can
differ of tens of MeV. Tools for the study of nucleon
resonances is πN experiments by electro-magnetic
probe. The availability of high intensity and high duty
cycle electron and photon facilities open new
possibilities for the study of baryon resonances using
electromagnetic probes. These provide information on
the resonances and nucleon wavefunctions through the
measurement of the helicity amplitudes, i.e. the
electromagnetic couplings between nucleon ground
state and initial states. In addition electroproduction
also allows us to explore baryon structure for different
distance scales by varying the photon virtuality.
Nowadays electro-excitation processes are a
fundamental tool to pursue these studies.
Meson Photoproduction
Experimentally, the density of states of the baryon
resonances in the mass region above 1.8 GeV is much
Figure 1: Total photoabsorption cross section
and exclusive cross sections for single-meson
and multimeson production. (a) Total, pπ0, p
p '; (b) total, K+, K
+, K
0; (c) p ,p , p ,
, , ; (d) pπ+π
-, pπ
0π
0, pπ
0
pπ+π
-π
0, pK
+K
-.
smaller than expected. A reason might be [1, 2] that
these missing resonances decouple from the πN
channel.
Then they escape detection in πN elastic scattering.
These resonances are expected to have no
anomalously low helicity amplitudes; then they must
show up in photo-production of multiparticle final
states.
From the electroproduction of baryon resonances
helicity amplitudes, form factors, and generalized
polarizabilities (inaccessible to πN scattering) can be
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
38
extracted. Intense experimental and theoretical efforts
have been devoted to determinations of the E2/M1
(electric quadrupole versus magnetic dipole) and
C2/M1 (longitudinal electric quadrupole versus
magnetic dipole) ratio for the N (1232) transition
amplitude. The total photoabsorption cross section
shown in Fig. 1 exhibits a large peak ( b) due to
(1232) production, shows some structures in the
second and third resonance regions, and levels off at
about b at a few GeV [3].
Polarization observables
The differential cross section for electroproduction
of pseudoscalar mesons off nucleons is given by the
product of the flux of the virtual photon field—with
longitudinal (L) and transverse (T) polarization—and
the virtual differential cross section, which depends on
six response functions (Ri = RT , RL , RTL , RTT , RTL' ,
RTT' ). The response functions depend on two additional
indices characterizing the target polarization and the
recoil polarization of the final-state baryon.
Thanks to polarization observables it is possible to
separate overlapping resonances.
The Gerasimov-Drell-Hearn sum rule
The photoproduction cross section depends on the
helicity of proton and photon. The Gerasimov-Drell-
Hearn (GDH) relates the integral over the helicity
asymmetry of the total absorption cross section for
circularly polarised photons on a longitudinally
polarised nucleon target to the nucleon anomalous
magnetic moment k, the spin S and the mass M:
2
2 2
24
th
p a
GDH
eI d k S
M (1)
where ζp and ζa are the total absorption cross
sections for parallel and antiparallel relative spin
configurations respectively, and the cross section is
weighted by the inverse of the photon energy .
The lower limit of the integral, th , corresponds to the
inelastic threshold of the reaction which, in the case of
the nucleons, is the pion photoproduction threshold.
Measurements of the helicity difference on exclusive
final states provide an important input to partial-wave
analyses.
Daliz decay
Dalitz decay, e e is the second most
important decay channel of the neutral pion with a
branching ratio of (1.198±0.032)%, while the dominant
decay mode, has a branching ratio of (98.798
± 0.032)% . The interest of the Dalitz decay lies in the
fact that it provides information on the semi off-shell
transition form factor 0 *F in the time-like
region, and more specifically on its slope parameter a .
The muon g−2 is one of the most precisely measured
and theoretically best investigated quantities in particle
physics. Our interest in very high precision
measurements is motivated by eagerness to exploit the
limits of our present understanding of nature and to
find effects which cannot be explained by the
established theory. More than 30 years after its
invention this is still the SM of elementary particle
interactions, a SU(3)c⊗SU(2)L⊗ U(1)Y gauge theory
broken to SU(3)c⊗U(1)em by the Higgs mechanism,
which requires a not yet discovered Higgs particle to
exist.
As important as charge, spin, mass and lifetime, are
the magnetic and electric dipole moments which are
typical for spinning particles like the leptons. Both
electrical and magnetic properties have their origin in
the electrical charges and their currents. Magnetic
monopoles are not necessary to obtain magnetic
moments. On the classical level, an orbiting particle
with electric charge e and mass m exhibits a magnetic
dipole moment given by
2L
eL
m (2)
where L mr v is the orbital angular
momentum. An electrical dipole moment can exist due
to relative displacements of the centers of positive and
negative electrical charge distributions. For a particle
with spin the magnetic moment is intrinsic and
obtained by replacing the the angular momentum
operator L by the spin operator
2S (3)
where is the Pauli spin matrices. Thus,
generalizing the classical form (2) of the orbital
magnetic moment, one writes
02
m gQ (4)
where 0
2
e
m, Q is the electrical charge in units
of e, Q=−1 for the leptons (l = e, μ, η ), Q=+1 for the
antileptons and m is the mass. The equations define the
gyromagnetic ratio g (g-factor) quantity exhibiting
important dynamical information about the leptons.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
39
The deviation from the Dirac value g /2=1, obtained
at the classical level, is anomalous magnetic moment:
2
2
ll
ga (5)
Figure 2. Spin precession in the g−2 ring
(∼12°/circle).
The measurement of aμ is illustrated in Fig. 2 [6].
When polarized muons travel on a circular orbit in a
constant magnetic field, then aμ is responsible for the
Larmor precession of the direction of the spin of the
muon, characterized by the angular frequency
a
eBa
m (6)
From comparison standard model theory and
experiment one could obtain:
exp 1027.6 8.1 10 3.4tha a (7)
Is there ―new physics‖?
The various components of the g-2 is QED, weak
contribution, hadronic vacuum polarization and
hadronic light by light. The most problematic set of
hadronic corrections is that related to hadronic light-
by-light scattering. Such contributions can be
dramatically enhanced and thus represent an important
contribution which has to be evaluated carefully. The
problem is that even for real-photon light-by-light
scattering, perturbation theory is far from being able to
describe reality, showing sharp spikes of π0, η and η'
production, while pQCD predicts a smooth continuum.
Experimental set-up
The new experimental setup of the recently established
BGOOD collaboration consists of the combination of
an open-dipole forward spectrometer and the BGO ball
of the former GRAAL collaboration to cover the
central angular region. This configuration is ideally
suited to investigate the photoproduction of multi-
particle final states with mixed charges. In addition it
will allow nucleon polarization measurements in
single-meson photoproduction. Due to the excellent
forward acceptance it opens the possibility to
investigate vector-meson production in order to
understand the reaction mechanism and the role of
resonances.
The BGOOD collaboration presently includes
individuals and groups from Germany (Bonn), Italy
(Rome, Frascati, Pavia, Messina), Russia (Gatchina,
Moscow), UK (Edinburgh, Glasgow) and Ukraine
(Kharkov), and is open for further extension.
The experimental set-up consists of a large 90 ton
dipole magnet, tracing detectors, two scintillating fiber
detectors, MOMO and SciFi2 (to allow for momentum
reconstruction of charged particles bent through the
magnetic field), an aerogel Cherenkov detector
(discriminates pions against protons and particularly
improves the K±-identification substantially), a time-
of-flight (TOF) detector (provides flight-time
measurements for charged particles and neutrons), the
BGO Ball hermetically encloses the target (polar
angular range 25- 155 degrees). The BGO (Bi4Ge3O12)
Ball is made of 480 truncated pyramidal crystals,
mechanical structure consists 24 carbon fibre baskets
(each containing 20 crystals) and external steel support.
The baskets keeps crystals separated, mechanically and
optically. The photomultiplier tubes (readout of the
crystals) coupled directly to the crystals. By this way
obtains an excellent energy resolution also at low
energies.
The target cell is a 4 cm diameter aluminum cylinder,
closed by thin mylar windows at the two sides, filled
by liquid Hydrogen (H2) or Deuterium (D2). The target
placed along the photon beam direction and
surrounded by BGO Ball hermetically. The
hydrogen/deuterium gas is cooled down by the helium
using heat exchangers and liquefied inside the cell. The
working temperature of the liquid Hydrogen or
Deuterium is about 17 K and 22 K respectively.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
40
Figure 3. The invariant γ γ mass spectrum
obtained with the Crystal Ball detector.
Figure 4. Energy balance (all quantity was directly
measured) and invariant mass in the final state: no cut
(red), a cut on Fermi momentum of Spectator in
Deuteron Target lower than 0.2 GeV/c and on Neural
Network variable higher than 0.8 were applied (black).
We are interesting in the channel with pseudoscalar
meson p PS p , wich decay to
PS e+e
- or PS e
+e
-e
+e
-. Where
pseudoscalar meson (π0, η and η') as much as possible
near threshold. Our goal is to identify (PS) thanks to
the missing mass of the system ( p–p') and then study
the PS decay product (Fig.3).
Recent relevant results of our analysis
By analysing the experimental data of Graal
experiment we identify the invariant mass of π0 and η
from Daliz decay e+e
-. About η': it is not possible to
measure with enough statistics because at Graal the
energy E is up to 1.5 GeV, only 50 MeV over the
threshold of η' production. By looking the invariant
mass obtained without any cuts application, the meson
reconstruction by two charged particle and one neutral
particle in the BGO is strongly dominate by π+π
-π
0 or
similar multiple pion channels (Fig.4).
Finally by applying our cuts, we was able to measure
and distinguish the π0 and η events, see the
reconstructed invariant mass in Fig.5. The statistics
available at Graal is not enough to extract the
observables presented in this measurement, but this
work result very promising at BGO-OD for the higher
intensity of the beam and the larger solid angle of
detection available in the new experiment.
Figure 5. Reconstructed invariant mass of π0 and η.
References [1] Koniuk, R., and N. Isgur, Phys. Rev. D 21 (1980) 1868; [2] Koniuk, R., and N. Isgur, Phys. Rev. Lett. 44 (1980) 845;
[3] Klempt E. and Richard J.-M.: Baryon spectroscopy, Rev. Mod.
Phys., Vol. 82 (2010 ) No. 2, 1-59; [4] Gerasimov S. B., 1966, Sov. J. Nucl. Phys. 2, 430, Yad. Fiz.
(1966) 2, 598; [5] Drell, S. D., and A. C. Hearn, Phys. Rev. Lett. ( 1966)16, 908;
[6] F. Jegerlehner, A. Nyffeler , Physics Reports 477 (2009) 1–110.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
41
STUDY OF NUCLEAR EQUATIONS OF STATE: THE ASY-EOS
EXPERIMENT AT GSI
S. Santoroa,b
for ASY-EOS collaboration
a)Dottorato in Fisica dell’Università di Messina, Dip.to di Fisica, V.le F.S. D’Alcontres ,98166 S. Agata-Messina, Italy
b) INFN-Gruppo Collegato di Messina, Messina, Italy
The study of the symmetry energy at nuclear
densities up to few time over the saturation value (~
0.15 fm-3
) constitutes an important task to improve
knowledge for the physics of heavy ion collisions (with
stable and radioactive beams) and astrophysics due to
the strict link with neutron stars studies. The AsyEos
collaboration has proposed an experiment at GSI
(S394) in order to study the nuclear collisions 197
Au
+197
Au,96
Ru +96
Ru and 96
Zr +96
Zr at 400 MeV/nucleon
incident energy with the SIS accelerator. In this
experiment the Land neutron detector, the Aladin
ToFWall, the forward part of the Chimera device and
the Si-CsI Krakow array have been used with the goal
to study the neutron and protons elliptic flows in an
optimized experimental conditions and with improved
statistics respect to the previous Fopi experiments
devoted to measure the observables that we want to
study. The reaction Au+Au has been successfully
performed in May 2011. We will present, after a brief
summary of the main motivations of the experiment,
the first results relative to the response of various
devices used. In particular the preliminary results of
the charge high identification obtained by means fast-
slow technique in the Chimera CsI detectors will be
shown.
Introduction
A key question in modern nuclear physics is the
knowledge of the nuclear Equation Of State (EOS)
and, in particular, of its dependence on density and on
asymmetry, i.e., on the relative neutron-to-proton
abundance [1, 2, 3, 4]. The EOS can be divided into a
symmetric term (i.e., independent from the isospin
asymmetry N Z
IN Z
, where N and and Z are the
numbers of neutrons and protons, respectively) and an
asymmetric term (also known as the symmetry energy)
that is proportional to the square of the isospin
asymmetry I [3,4,5]. Measurements of isoscalar
collective vibrations, collective flow and kaon
production [1,6,7] in energetic nucleus-nucleus
collisions have constrained the behaviour of the
equation of state of isospin symmetric matter for
densities up to five times the saturation density ρ0. On
the other side, the EOS of asymmetric matter is still
subject to large uncertainties. Besides the astrophysical
interest, e.g. neutron star physics and supernovae
collapse [8,9], the density dependence of the symmetry
term is of fundamental importance for nuclear physics.
The thickness of the neutron skin of heavy nuclei
reflects the differential pressure exerted on the core
[10] and the strength of the three-body forces, an
important ingredient in nuclear structure calculations
[11], represents one of the major uncertainties in
modeling the equation of state at high density [1,12].
Moreover, properties of exotic nuclei, i.e., nuclei far
away from stability valley, and the dynamics of nuclear
reactions rely on the density dependence of the
symmetry energy [3,4]. In the last decade,
measurements of the Giant Monopole [13], Giant
Dipole [14] and Pygmy Dipole [15] resonances in
neutron-rich nuclei, isospin diffusion [16,17], neutron
and proton emissions [18], fragment isotopic ratios
[17,19,20] and isospin dependence of competition
between deep-inelastic and incomplete fusion reactions
[21] have provided initial constraints on the density
dependence of the symmetry energy around and below
saturation density ρ0. It results that the best description
of experimental data is obtained with a symmetry
energy )u(C)u(C)u(S sym
pot
3/2sym
kin with in the
range 0.6-1.1 [17] ( 0/u is the reduced nuclear
density). In the near future, extensions of these
measurements with both stable and rare-isotope beams
will provide further stringent constraints at sub-
saturation densities. In contrast, up to now, very few
experimental constraints exist on the symmetry energy
at supra-saturation densities ( 1u ). This is the
domain with the greatest theoretical uncertainty and the
largest interest for neutron stars. The behaviour of the
symmetry energy at supra-saturation densities can only
be explored in terrestrial laboratories by using
relativistic heavy-ion collisions of isospin asymmetric
nuclei. Reaction simulations propose several
potentially useful observable which should be sensitive
to the behavior of the symmetry energy at supra-
saturation densities, such as neutron and proton
flows(direct and elliptic) [4,22,23], neutron/proton
ratio [4,17,24, 25], / ratio and flows [4,22,26], 0/K K [27] and / [26] ratios.
To this day the problem is still open. Few works have
provided constraints on symmetry energy behaviour at
supra-saturation densities. The double ratio
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
42
Zr
0
Ru
0 )K/K/()K/K( was measured in 96
Ru
+96
Ru and 96
Zr +96
Zr collisions at 1528 MeV/nucleon
using the FOPI detector at GSI [28]; the experimental
results show good agreement with the prediction of a
thermal model in the case of the assumption of a soft
symmetry energy for infinite nuclear matter. More
realistic simulations in the frame of transport theory,
for finite nuclear matter, show a similar good
agreement with the data, but also exhibit a quite
insensitivity to the symmetry term. However, it has
recently been pointed out that more experimental and
theoretical work are needed to establish the
effectiveness of the0/K K ratio in probing the
symmetry energy [4]. The single ratio / was
measured in 197
Au +197
Au [29] and analyzed using the
hadronic transport model IBUU04 [30]. The results
suggest that the symmetry energy is rather soft at
supra-saturation densities; this finding, symmetry
energy reaches its maximum at a density between ρ0
and 2ρ0 and then starts decreasing at higher densities, is
not consistent with the density dependence deduced
from fragmentation experiments probing nuclear
matter near or below saturation density [17] and with
the slightly softer density dependence resulting from
the analysis of the pygmy dipole resonance in heavy
nuclei [15]. Moreover, other theoretical works [31]
suggest a reduced sensitivity of / ratio to the
symmetry energy. Recently, the same set of FOPI data
has been analyzed in the framework of the IMproved
Isospin dependent Quantum Molecular Dynamics (Im-
IQMD) [32]; it results a very stiff symmetry energy of
the potential term proportional to u with 2 , just
the opposite of [30] results.
Fig. 1. - Asy-Stiff (F15) and Asy-Soft (F05)
parameterizations of symmetry potential energy
of nucleons as a function of the reduced nuclear
density u, as used in UrQMD calculations; from
ref. [36]
It follows that also for the / ratio further work
is needed to establish the effectiveness in probing the
symmetry energy. In-medium absorption and re-
emission of pions can distort the asymptotic
experimental signal and it is not clear which density of
matter is explored by the pions signal. The analysis of
another set of FOPI data is described in the third
section of this paper.
Neutron and proton elliptic flows
One of the most promising probe of the symmetry
energy strength at supra-saturation densities is the
difference of the neutron and proton (or hydrogen)
elliptic flows [33,34,35]. This has emerged mainly
from calculations based on the Ultra-Relativistic
Quantum Molecular Dynamics model (UrQMD) [37].
We report here some results obtained using UrQMD
for the 197
Au+197
Au collision at 400 MeV/nucleon. The
calculations have been performed using both Asy-Stiff
( 1.5 ) and Asy-Soft ( 0.5 ) potential
symmetry energies, indicated as F15 and F05,
respectively, in Fig. 1. A realistic description of the
clustering processes during the evolution of the
reaction is crucial for predicting dynamical properties
of free neutrons, protons and light charged particles. In
the UrQMD, the clustering algorithm is based on the
evaluation of the proximity of nucleons in the phase
space by using two parameters: the relative nucleon
coordinates (Δr) and the relative momenta (Δp). The
results presented here have been obtained using the
cluster distributions built after a reaction time of 150
fm/c. The proximity parameters were: Δr=3.0 fm and
Δp=275 MeV/c which are typical for QMD models
[38]. As an example of the clusterization procedure, the
charge distribution obtained for central collisions of
Au+Au is shown in Fig. 2 in comparison with the data
of Reisdorf et al. [39]. With a normalization at Z = 1,
the overall dependence on Z is rather well reproduced
but the yields of Z = 2 particles are under predicted by
about a factor 3. The strong binding of 4He particles is
beyond the phase-space clustering criterion used in the
model. However, also the 4π integrated yields of
deuterons and tritons in central collisions are
underestimated by similar factors of 2 to 3.
The UrQMD predictions for the elliptic flow of
neutrons, protons, and hydrogen as a function of
rapidity in laboratory reference system Ylab for mid-
peripheral collisions (impact parameter 5.5 < b < 7.5
fm) and for the two choices of the density dependence
of the symmetry energy, are shown in Fig. 3. We
remind here that direct 1v and elliptic 2v flows
are obtained by the azimuthal particle distributions
with the usual Fourier expansion:
)2cos(2)cos(21)(f 11 (1)
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
43
Fig. 2. - Fragment yields, integrated over the
4π solid angle, in central (equivalent to impact
parameter b < 2:0 fm) collisions of 197
Au+197
Au
at 400 MeV/nucleon as a function of Z (dots,
from Ref. [29]) in comparison with UrQMD
predictions normalized at Z=1 (histogram);
adapted from Ref. [40].
with representing the azimuthal angle of the
emitted particle with respect to the reaction plane [41].
The dominant difference is the significantly larger
neutron squeeze-out in the Asy-Stiff case (upper panel)
compared to the Asy-Soft case (lower panel). The
proton and hydrogen flows respond only weakly, and
in opposite direction, to the variation of within the
interval of interest. Another interesting observable is
the ratio of neutron and proton yields as a function of
the transverse momentum pt (i.e. the component of
momentum perpendicular to the beam direction).
ASY-EOS experiment at GSI
The experiment S394, "Constraining the Symmetry
Energy at Supra- Saturation Densities With
Measurements of Neutron and Proton Elliptic Flows",
was devoted to measurements of neutron and proton
elliptic flows in isospin asymmetric systems 197
Au
+197
Au,96
Ru +96
Ru and 96
Zr +96
Zr at 400 MeV/nucleon.
Simultaneous measurements of neutron-proton yield
ratio, flow and isotopic ratio for light fragments was
performed; all these measurements could allow to
compare the symmetry energy as extracted by using
several different nucleon-based observable. The
Au+Au system is heavy and neutron-rich. Simulations
with UrQMD predict large sensitivity of the symmetry
energy on the neutron-proton observable for this
system. Using Ru+Ru and Zr+Zr systems could allow
us to compare neutron-rich and neutron-deficient
systems; the 96
Ru and 96
Zr combination is unique
among available stable isotopes in that it is mass
symmetric and isobaric. The measurement with these
systems are very important in order to reduce
systematic errors. Besides, the collected data could
provide important information to pin up effects related
Fig. 3. - Elliptic flow parameter for mid-
peripheral (impact parameter 5.5 < b < 7.5fm) 197
Au +197
Au collisions at 400 MeV/nucleon as
calculated with the UrQMD model for neutrons
(dots), protons (circles), and all hydrogen
isotopes (Z=1, open triangles), integrated over
transverse momentum pt, as a function of the
laboratory rapidity Ylab. The predictions
obtained with a stiff and a soft density
dependence of the symmetry term are given in
the upper and lower panels, respectively. The
experimental result from Ref. [42] for Z = 1
particles at mid-rapidity is represented by the
filled triangle (the horizontal bar represents the
experimental rapidity interval); adapted from
Ref. [40].
to the size, the total charge and the surface of the
nuclear system. This experiment aims to achieve high
quality of the analysis by increasing the statistics by
factor expected to be around 20-30 compared to the
previous experiments.
Fig. 4. - Schematic view of experimental setup.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
44
Fig. 5. - Fast vs Slow component scatter plot as
obtained in a CHIMERA CsI(Tl) scintillator
placed at a polar angle 9lab for Au+Au
reaction at 400 MeV/nucleon at GSI; lines of
particles stopped and passing through CsI
detector are indicated by arrows.
During the experiment (see Fig. 4 for a schematic
view) we used LAND [46], time-of-flight detector for
high energetic neutrons and light charged particles in a
similar geometry like in [43] to measure neutron
squeeze-out. LAND has been positioned around
45lab , to cover the mid-rapidity for a large
transverse momentum region. Protons can be separated
by employing the calorimetric properties of the neutron
detector and the measured proton observable can be
compared directly to the FOPI data measured in a
similar angular acceptance. The simultaneous
measurement of the atomic number Z and the
azimuthal angle for fragment emissions in the forward
direction will be essential for a precise determination
of the modulus and orientation (reaction plane) of the
impact parameter; this task has been accomplished by
using a detection system with high granularity at
forward angles ( 7 20lab ) consisting of 8 CsI
rings (352 modules) of the CHIMERA multi-detector
[47] and the ALADIN Time-Of-Flight wall [48].
Preliminary results revealed a good charge
identification performance for light charged particles
using the fast-slow technique in the CsI detectors
(Fig.5) and the capability of reconstructing the reaction
plane. In addition, flow of light fragments have been
measured with the Krakow telescope array positioned
on the opposite side of LAND, at angles
( 21 60lab ). The use of digital acquisition
techniques [49] in about 10 % of the detectors, in
parallel to standard analogical one, has been of
fundamental importance allowing us to store directly
the shape the electronic signals; an off-line analysis is
then useful in order to study the best processing system
and to develop new electronic solutions.
Conclusions
New experiments on symmetry energy at supra-
saturation densities are expected to take place during
the next few years, in Europe as well as worldwide. It
is likely that providing definitive constraints on the
symmetry energy will require simultaneous
measurements of several observable. However, the
isospin signals at supra-saturation densities appear to
be controversial and strongly model dependent; to
clarify these points, we need a better understanding of
volume, Coulomb and surface effects, production and
reabsorption of resonances, reaction dynamics, in-
medium nucleon-nucleon cross section, splitting of
neutron and proton effective masses in momentum
dependent iso-vectorial interactions. Neutron and
proton elliptic flows appear to be as one of the most
interesting observable with strong sensitivity to
symmetry energy. The ASY-EOS experiment at GSI
was performed properly to measure such and other
isospin sensitive observable in reactions of isospin
asymmetric systems at pre-relativistic energies, in
order to provide quantitative information on the density
dependence of symmetry energy at supra-normal
saturation density.
The author would like to thank the people that made
this work possible: the whole INFN-CHIMERA-
EXOCHIM collaboration in Catania, Messina, Naples
and Milano, the GSI-Group and the ASY-EOS
collaboration for their support and exceptional work.
References [1] Fuchs C. and Wolter H.H., Eur. Phys. J. A, 30 (2006) 5;
[2] KlÄahn T. et al., Phys. Rev. C, 74 (2006) 035802;
[3] Baran V. et al., Phys. Rep., 410 (2005) 335; [4] Li B.-A. et al., Phys. Rep., 464 (2008) 113;
[5] Lattimer J.M. and Prakash M., Science, 304 (2004) 536;
[6] Danielewicz P. et al., Science, 298 (2002) 1592; [7] Youngblood D.H. et al , Phys. Rev. Lett., 82 (1999) 691;
[8] Lattimer J.M. and Prakash M., Phys. Rep., 333 (2000) 121;
[9] Botvina A.S. and Mishustin I.N., Phys. Lett. B, 584 (2004) 233; [10] Horowitz C.J. and Piekarewicz J., Phys. Rev. Lett., 86 (2001)
5647;
[11] Wiringa R.B. and Pieper S.C., Phys. Rev. Lett., 89 (2002) 182501;
[12] Chang Xu and Li B.-A., Phys. Rev. C, 81 (2010) 064612;
[13] Li T. et al., Phys. Rev. Lett., 99 (2007) 162503; [14] Trippa L. et al., Phys. Rev. C, 77 (2008) 061304;
[15] Klimkiewicz A. et al., Phys. Rev. C, 76 (2007) 051603;
[16] Tsang M.B. et al., Phys. Rev. Lett., 92 (2004) 062701; [17] Tsang M.B. et al., Phys. Rev. Lett., 102 (2009) 122701;
[18] Famiano M. et al., Phys. Rev. Lett., 97 (2009) 052701;
[19] Iglio J. et al., Phys. Rev. C, 74 (2006) 024605;
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
45
[20] Tsang M.B. et al., Phys. Rev. Lett., 86 (2001) 5023;
[21] Amorini F. et al., Phys. Rev. Lett, 102 (2009) 112701; [22] Yong G.-C. et al., Phys. Rev. C, 74 (2006) 064617; Yong G.-C.
et al., Phys. Rev. C, 73;
[23] Greco V. et al., Phys. Lett. B, 562 (2003) 215; [24] Li B.-A. et al., Phys. Lett. B, 634 (2006) 378;
[25] Li Q. et al., Phys. Rev. C, 73 (2006) 051601;
[26] Li Q. et al., Phys. Rev. C, 71 (2005) 054907; [27] Ferini G. et al., Phys. Rev. Lett., 97 (2006) 202301;
[28] Lopez X. et al., Phys. Rev. C, 75 (2007) 011901;
[29] Reisdorf W. et al., Nucl. Phys. A, 781 (2007) 459; [30] Xiao Z. et al., Phys. Rev. Lett., 102 (2009) 062502;
[31] Li Q. et al., J. Phys. G, 32 (2006) 407;
[32] Zhao-Qing Feng, Gen-Ming Jin,, Phys. Lett. B, 683 (2010) 140;
[33] Trautmann W. et al., arxiv:0907.2822, (2009);
[34] Trautmann W. et al.,, Prog. Part. Nucl. Phys., 62 (2009) 425; [35] Trautmann W. et al.,, Int. J. Mod. Phys.E, 19 (2010) 1653;
[36] Li Q. et al., J. Phys. G, 31 (2005) 1359;
[37] see UrQmd homepage, www.urqmd.org;
[38] Yingxun Zhang and Zhuxia Li,, Phys. Rev. C, 74 (2006)
014612; [39] Reisdorf W. et al., Nucl. Phys. A, 612 (1997) 493;
[40] Russotto P. et al., in Proceedings of the XLVI International
Winter Meeting On Nuclear Physics, edited by Iori I. and Tarantola A. (Università degli Studi di Milano) 2008, pp. 54-
62;
[41] Andronic A. et al., Eur. Phys. J. A, 30 (2008) 31; [42] Andronic A. et al., Phys. Lett. B, 612 (2005) 173;
[43] Leifels Y. et al., Phys. Rev. Lett., 71 (1993) 963;
[44] Lambrecht D. et al., Z. Phys. A, 350 (1994) 115; [45] Li Q. et al., Mod. Phys. Lett. A, 9 (2010) 669;
[46] Blaich Th. et al., Nucl. Instrum. Methods Phys. Res. A, 314
(1992); [47] Pagano A. et al., Nucl. Phys. A, 734 (2004) 504;
[48] SchÄuttauf A. et al., Nucl. Phys. A, 607 (1996) 457;
[49] Amorini F. et al., IEEE Trans. Nucl. Sci., 55 (2008) 717;
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
47
PREMIO APP PER UNA TESI DI DOTTORATO
Paolo V. Giaquinta
Università degli Studi di Messina
Quest‘anno è stata celebrata la prima edizione del
premio conferito congiuntamente dall‘Accademia
Peloritana dei Pericolanti (APP) - segnatamente, dalla
―Classe di Scienze Fisiche, Matematiche e Naturali‖
della stessa Accademia - e dal Corso di Dottorato di
Ricerca in Fisica all‘autore della tesi di dottorato,
afferente al XXIII ciclo, distintasi particolarmente per
originalità e contenuti. La valutazione delle tesi
presentate dai candidati al premio è stata effettuata da
una commissione insediata ad hoc dal Collegio dei
Docenti del Corso di Dottorato; la commissione era
presieduta dal Prof. Lorenzo Torrisi, Coordinatore del
Corso di Dottorato, ed era composta dai Proff.
Giuseppe Carini, Giorgio Giardina, Domenico
Majolino e Paolo V. Giaquinta, quest‘ultimo anche
nella qualità di Direttore della Classe di Scienze
FF.MM.NN. dell‘Accademia Peloritana dei Pericolanti.
La commissione, riunitasi il 20 aprile 2011, ha
deliberato all‘unanimità di assegnare il premio al Dott.
Alessandro Ridolfo per la tesi intitolata “Quantum
optical properties of strongly coupled systems” , con la
seguente motivazione:
“La tesi del Dr. Ridolfo, di cui si riporta in calce il
sommario, riguarda una trattazione quantistica nel
campo dell’opto-elettronica. Nanoparticelle e
nanostrutture sono capaci di focalizzare fotoni a
dimensioni più piccole della lunghezza d’onda. In tal
modo è possibile aumentare la densità ottica degli stati
anche in una microcavità. La tesi affronta lo studio
teorico di questi sistemi quantici. Le indagini effettuate
fanno prevedere la possibilità di migliorare in futuro
dispositivi quanto-fotonici, basati su semiconduttori, di
dimensione nanometrica che possono essere sensibili
anche a fotoni singoli e che possono adoperarsi per
emissioni di luce laser da dispositivi nanometrici. La
trattazione approfondita del problema, l’approccio
quantistico adoperato, l’originalità della tematica
affrontata e le possibili ricadute applicative che i
dispositivi a semiconduttore potrebbero avere, hanno
contribuito a fare giudicare la tesi del Dr. Ridolfo di
elevata qualità, originalità e approfondimento, ben
meritevole dunque del premio in oggetto.”
L‘attestato di merito è stato consegnato dal Prof. Paolo
V. Giaquinta al Dott. Alessandro Ridolfo in occasione
della II Giornata di Studio del Dottorato di Ricerca in
Fisica. Il premio conferito dà anche titolo alla
pubblicazione di un ampio estratto della tesi sugli “Atti
della Accademia Peloritana dei Pericolanti (AAPP) - Classe di Scienze Fisiche, Matematiche e Naturali” ,
una rivista scientifica multidisciplinare pubblicata in
formato elettronico e liberamente accessibile sul
dominio internet: http://www.actapeloritana.it.
Sommario della Tesi
QUANTUM OPTICAL PROPERTIES OF STRONGLY
COUPLED SYSTEMS
“The realization of solid state devices able to control
the single photon states is of great importance in the
field of Quantum Information and Opto-electronics. Re- cently, significant developments have been
achieved by coupling single quantum emitters (QEs) in
optical microcavities with high Q factor. The main
limitation of these devices is represented by the size of the cavities that can not be smaller than half wavelength, and in practice are much larger because of the presence of mirrors or photonic crystals required to
obtain the optical confinement. However, nanopar- ticles (NPs) and metallic nanostructures are able to
focus the electromagnetic waves to spots much smaller
than a wavelength. In this way, it is possible to increase
the optical density of states, as well as with the
microcavity, but with more compact structure. The
ability of metal NPs to control the radiative decay of the QEs nearly positioned has been widely
demonstrated both theoretically and experimentally. In
this thesis I’ve been studied, from the theoretical point
of view, the optical proper- ties of these quantum
systems, in various coupling regime. In the first part it
was developed a theoretical framework based on the
calculation of the Master Equation (ME), which has
helped to investigate the photoluminescence’s
properties of micro- cavity coupled to QEs optically
excited via incoherent pumping. In such systems, under
low excitation density, it was possible to obtain
analytical formulas that de- scribe the processes
associated with the first-order correlations
(photoluminescence spectra). The results obtained from
the fit of the experimental data show an excel- lent
agreement with our theoretical results. In particular, it has been shown highly predictive nature in the case of photonic polaritons in an organic double microcav- ity: the fit of the photoluminescence of one of the two
microcavities has enabled the calculation of the
photoluminescence of the whole structure (A. Ridolfo
et al. Phys. Rev. B 81, 075313 (2010)). At high-density
excitation, calculation’s technique in non-perturbative
regime (based on the truncation of the number of photons) has led to some important results in the study
of nonlinear optical processes. Subse- quently, the ME
formalism was extended to the case of structures made
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
48
of metal NPs coupled to QES that, because of their
spectroscopic properties, are also called artificial
hybrid molecules. The extension of the theoretical
framework was made possible by modeling the
appropriate electromagnetic field which arises from the
presence of electronic excitations on the surface of metal NPs called plasmons. The results, which refer to
the silver NPs, show that the inelastic part of the
resonance fluorescence increases more than two orders
of magnitude than the QE alone. It also reported a
careful study of the statistical properties of the
scattered light by calculating the second order
correlation function, which is strongly influenced by
the presence Fano effect, originating from the
interaction between the QE discrete excitation and the
continuous band of plasmon. The calculation of the
scattering spectra and of the intensity correlations, shows that this system can be used as a single photon
ultra-compact optical transistor: the scattering of a first
photon of appropriate frequency, is able to activate (or
inhibit) the scattering of a second photon (A. Ridolfo et
al., Phys. Rev. Lett (in press)). In the next chapter, with
ac- curate calculations of electromagnetic scattering
based on the T-matrix, it has been demonstrated that it
is possible to realize the strong coupling regime in the
case of many QEs and single QE (S. Savasta et al., ACS Nano, 4, 6369 - 6376 (2010)). In the first case, the cross section of extinction, calculated for a
structure consisting of a silver nanoparticle coated with
a dielectric matrix doped with photoluminescent
molecules, has showed the characteristic anticrossing
typical of the strong coupling regime. In the second
case, replacing the single-nanoparticle geometry with
the two-nanoparticle geometry in order to obtain an
increase of the plasmonic field in the center of the
principal axis to obtain the strong coupling regime with
a single QE. Again, calculations have showed the
achievement of the regime of strong inter- action in a
structure whose maximum size is only 40 nm! From
the results obtained thus good prospectives emerge for
possible applications in Quantum Information or to
create devices that can process individual photons. This
will make it pos- sible to implement devices for
Photonic Quantum Computation without renounce to
the nanometric dimensions of the compact modern
nano-sized semiconductor logical gates. In the second-last chapter has been presented a theoretical analysis of all-optical control of the strong coupling regime
(dynamic switching-on/off) be- tween a single QE and
an optically confined microcavity-mode, by sending
optical pulses control of appropriate area, able to
determine transitions to and from the third lower level
energy of the QE (A. Ridolfo et al., Phys. Rev. Lett (in
press)). The chosen scheme describes the system
recently used in experiments on adiabatic- switching
for inter-sub-polaritons (Guenter G. et al. Nature 458, 178 (2009)), but it can also be applied to the study of optical transitions exciton-biexciton cascade or other
transitions, in which are present the cavity polaritons. From our results, important conclusions are drawn
about the possibilities and limitations of the im- portant
experimental design proposed: once Rabi oscillations
have been induced with a first control pulse, depending
on the time of arrival of a second control pulse, Rabi
oscillations can be suppressed or not, also influencing
the coherence properties of the whole system. The
theoretical results obtained are very fascinating and
will stimulate the achievement of new experimental
and technology goals.
Finally, in the last chapter it has been studied the
dynamic behavior of en- tanglement in a system
consisting of two solid state QEs enclosed in two
separate microcavities. In this solid state system, in
addition to coupling with the cavity mode, the QE is
coupled to a continuum of modes that provide a lossy
channel to which is adds a further loss caused by the
phases losses induced by interaction with thermal
phonons. This configuration has been modeled as a
multiparty system consisting of two independent sub-parts, each containing a single q-bit and a single cavity
mode, subject to losses, radiative and non-radiative
decay (pure-dephasing). The theoretical results
obtained by the usual framework of ME already used
in pre- vious chapters have highlighted the important
destructive impact on the evolution of entanglement-dynamics caused by pure-dephasing. The experimental
informa- tion in these systems can be obtained from the
detection of the light escaping from the cavity. With an
appropriate choice of physical parameters of the model, corre- sponding to values that are extrapolated from the
experiments, was simulated the dynamic evolution of entanglement in two realistic situations (K. Hennessy
et al. Nature 445, 896 (2008) V . Loo V et al. arXiv: 1011.1155v1 [cond –mat.mes-hall] (2010)). Thus, the
work places emphasis on the negative impact of pure-dephasing, always present in solid state devices, on the
entanglement decay.”
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
49
PHD E MONDO DEL LAVORO: STATISTICHE SUL PLACEMENT POST –
DOTTORATO
Paola Donato
Dipartimento di Fisica, Università di Messina
Dottorato di Ricerca in Fisica, Università di Messina
1. Introduzione
È stato sfruttato il database del dottorato di ricerca in
Fisica per condurre un‘indagine sul placement dei
dottori di ricerca in Fisica dell‘Università degli Studi di
Messina relativamente ai cicli dal XIII al XXIII.
Occorre premettere che si è fatto in modo di curare e
far crescere il database del dottorato, strumento
indispensabile per questo tipo di analisi. Il database,
infatti, è stato avviato sin dal primo ciclo di dottorato
(1983) e, di anno in anno, aggiornato e integrato.
Ritengo sia di importanza fondamentale curare e
migliorare i dati in nostro possesso, poiché questi sono
in grado di restituirci una visione globale del lavoro
svolto dai docenti e dai dottorandi, oltre che una
valutazione complessiva della funzione didattico-
formativa del dottorato in vista della collocazione nel
mondo della ricerca e del lavoro. Proprio di
quest‘ultimo aspetto mi sono occupata in questa breve
indagine.
Altra importante premessa, inoltre, riguarda la scelta
di collocare questa indagine all‘interno di un range
temporale ristretto agli effettivi impieghi dichiarati da
sessanta dottori di ricerca in Fisica, dottorati negli
ultimi dieci anni (dal XIII al XXIII ciclo) presso il
Nostro Ateneo.
2. Macro-aree di impiego lavorativo post-doc
Per descrivere l‘andamento dell‘occupazione post-
dottorato si è ritenuto opportuno suddividere la
collocazione dei dottori di ricerca in Fisica in quattro
macroaree di impiego. Se da un lato, infatti, le
macroaree risultavano facilmente individuabili – i dati
rilevati evidenziavano la presenza di queste quattro
principali aree di impiego –, dall‘altra parte si voleva
tener conto di quegli sbocchi lavorativi meno presenti
per locazione geografica e/o territoriale, in modo tale
da rendere il futuro confronto con i dati statistici di altri
atenei il più possibile coerente.
Le aree scelte sono state quattro:
Università: All‘interno di questa macroarea
sono stati considerati i dottori di ricerca che a
oggi ricoprono il ruolo di ricercatori di ruolo,
ricercatori a tempo determinato, gli assegnisti
di ricerca, i borsisti post-doc;
Scuola: All‘interno di questa macroarea
rientrano tutti quei dottori di ricerca che sono
attualmente impiegati nella scuola secondaria
superiore;
Enti di ricerca e industrie: All‘interno di
questa macroarea abbiamo considerato quei
dottori di ricerca che sono occupati presso:
INFN, CNR, ENEA, Fondazioni, ST-
Microelectronics;
Altro: All‘interno di questa macroarea
abbiamo inserito tutte quelle attività lavorative
che non rientrano nelle tre precedenti aree.
3. Densità dei cicli
Un aspetto importante che si è deciso di prendere in
considerazione prima di addentrarci nel dettaglio delle
collocazioni lavorative dei dottori di ricerca, è stato
quello della scelta del curriculum all‘interno del corso
di dottorato. Il grafico (A) evidenzia che la principale
scelta dei dottorandi riguarda il curriculum di Struttura
della Materia, affiancato da quello di Fisica Nucleare e
seguito a distanza dai curricula di più recente
istituzione, cioè quelli di Fisica Applicata ai Beni
Culturali, di Fisica Applicata ai Beni Ambientali e
quello di Fisica della Materia Soffice e dei Sistemi
Complessi. L‘interesse del dato, ovviamente, risiede
nella sua successiva declinazione in funzione
dell‘impiego lavorativo. Ci è sembrato interessante, in
altre parole, rilevare come e in che misura la scelta del
curriculum può condizionare la tipologia di impiego
lavorativo post-doc. Occorre tenere presente che il dato
analizzato, di per sé già interessante, risulterà più
significativo quando disporremo di maggiori
informazioni relative ai curricula di più recente
istituzione.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
50
DENSITA’
DEI
CICLI
CICLO Struttura della
Materia
Fisica
Nucleare
Fisica della
Materia
Soffice e dei
Sistemi
Complessi
Fisica
Applicata ai
Beni
Culturali
Fisica
Applicata ai
Beni
Ambientali
XIII 4 1
XIV 5
XV 4
XVI 2 3 1
XVII 4 1
XVIII 3 2 2
XIX 4 2
XX 3 3 1
XXI 3 1
XXII 3 1 1
XXIII 4 1 1
Grafico A: Numero dei dottorandi di ricerca in Fisica divisi per curriculum dal ciclo XIII al ciclo XXIII
4. Dottorandi divisi per curriculum scelto
all’interno del Corso di Dottorato di Ricerca
e loro placement.
Il rapporto tra la densità dei cicli e l‘impiego
lavorativo post-dottorato ha consentito di individuare
quanto la scelta del curriculum abbia influenzato lo
sbocco lavorativo. Il numero dei dottori di ricerca che
hanno scelto il curriculum Struttura della Materia e
Fisica Nucleare – maggiore perché questi curricula
sono stati istituiti da maggior tempo rispetto agli altri –
è preponderante in tutti gli ambiti lavorativi. Desidero
evidenziare che sono i soli presenti nell‘ambito
universitario, probabilmente perché i relativi settori di
applicazione, a livello sia nazionale sia internazionale,
offrono maggiori opportunità di impiego.
I dati sono indicativi anche per ciò che riguarda
l‘impiego nel settore scolastico. Pur non essendo
storicamente l‘insegnamento uno degli sbocchi naturali
per i laureati in Fisica, nondimeno è possibile rilevare
come il mondo scolastico rappresenti una risorsa
lavorativa importante per coloro che conseguono un
dottorato di ricerca. Il dato riportato nel grafico (B),
più in particolare, ci restituisce una distribuzione nel
settore scolastico pressoché equa tra tutti i curricula
del dottorato.
Importante sbocco lavorativo, inoltre, è quello degli
enti di ricerca, quali, ad esempio, INFN, CNR, ST
XIII XIV XV XVI XVII XVIII XIX XX XXI XXII XXIII
0
1
2
3
4
5
Struttura della Materia
Fisica nucleare
Fisica della Materia Soffice e Sist. C.
Fisica Applicata ai Beni Culturali
Fisica Applicata ai Beni Ambientali
Densità
Ciclo
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
51
Microelectronics, Arpa. Non sono presenti in questa
macroarea, come evidenzia il grafico B, dottori di
ricerca in Fisica Applicata ai Beni Culturali e Beni
Ambientali. Quasi sicuramente quest‘ultimo dato è
legato ad una scelta di specializzazione che, già a
monte, è orientata ad una implementazione
maggiormente operativa delle conoscenze acquisite.
Quasi tutti i curricula, infine, contribuiscono alla
macroarea che abbiamo definito ―altro‖.
Scuola Università Enti di Ricerca Altro Totale
Struttura della Materia 9 21 4 2 36
Fisica Nucleare 2 9 4 1 16
Fisica della Materia
Soffice e dei Sistemi
Complessi
/ / 1 1 2
Fisica Applicata ai Beni
Culturali 3 / / / 3
Fisica Applicata ai Beni
Ambientali 2 / / 1 3
Totale 16 30 9 5 60
Grafico B: Dottorandi divisi per curricula scelto all’interno del Corso di Dottorato di Ricerca e loro placement.
Scuola Università Enti di Ricerca Altro
0
5
10
15
20
Struttura della Materia
Fisica nucleare
Fisica della Materia Soffice e Sist. C.
Fisica Applicata ai Beni Culturali
Fisica Applicata ai Beni Ambientali
Densità
Occupazione
5. Densità occupazionale
Considerando in modo più generalizzato il dato
relativo all‘impiego dei dottori di ricerca, prescindendo
cioè dal curriculum scelto, risulta una suddivisione
nelle macroaree come riportato nel grafico (C).
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
52
DENSITA’
OCCUPAZIONALE
CICLO SCUOLA UNIVERSITA’ ENTI DI
RICERCA
ALTRO TOTALE
XIII 1 4 5
XIV 1 2 1 1 5
XV 3 1 4
XVI 3 2 1 6
XVII 1 2 2 5
XVIII 4 2 1 7
XIX 1 5 6
XX 1 3 2 1 7
XXI 3 1 4
XXII 2 1 2 5
XXIII 1 4 1 6
TOTALE 16 30 9 5 60
Grafico C: Numero dei dottori di ricerca in Fisica dal ciclo XIII al ciclo XXIII e loro placement.
Il ruolo principale nel placement dei dottori di
ricerca viene svolto dall‘istituzione universitaria. Nel
grafico (D) si è cercato di evidenziare il rapporto tra i
dottori di ricerca che sono stati assorbiti dal mondo
universitario in modo strutturale e quelli che non hanno
ancora una collocazione stabile. Ci siamo soffermati su
questo aspetto sia per sottolineare come, in modo
analogo ad altri settori lavorativi della nostra società,
anche nel mondo universitario il lavoro precario svolga
una funzione preponderante rispetto a quello stabile,
sia per confrontare il dato in nostro possesso con
un‘altra importante realtà universitaria nazionale.
S c u o la U n i v e r s it à E n ti d i R i c e r c a A l tr o
0
5
1 0
1 5
2 0
2 5
3 0
De
ns
ità
O c c u p a z io n e
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
53
Grafico D
Come si può rilevare dal grafico (E), infatti, il dato
tendenziale risultante dai dati messi a disposizione
dall‘Università degli Studi di Roma Tor Vergata dal
XVIII al XXIII ciclo sono identici a quelli risultanti
dagli undici cicli presi in considerazione nell‘ateneo
messinese. Questo conferma che solo circa un quarto
dei dottori di ricerca riesce a rimanere in modo
permanente all‘interno del mondo universitario. Un
altro dato rilevante, a nostro parere, è che circa un terzo
degli strutturati viene assorbito dalle Università
straniere. Questo dato è importante perché conferma la
spendibilità all‘estero delle competenze acquisite nel
nostro dottorato di ricerca, sebbene ci ricordi, nel
contempo, che molte delle nostre migliori risorse non
riescono a trovare spazio nel mondo del lavoro e della
ricerca a livello nazionale.
Grafico E
6. Placement dei dottori di ricerca: un
confronto.
Nell‘ultimo grafico sviluppato (F) abbiamo messo a
confronto le tipologie occupazionali dei dottori di
ricerca in Fisica dell‘ateneo messinese e di quello
romano (Università Tor Vergata). Questo confronto è
finalizzato innanzitutto a comprendere le diverse
opportunità che il territorio offre a coloro che
proseguono gli studi universitari conseguendo il titolo
di dottore di ricerca. Ovviamente il dato si basa su
indicazioni che non possono essere considerate
esaustive, cosa che implicherebbe una ricerca a spettro
molto più ampio rispetto a quello preso in
considerazione in questa sede. Nondimeno, con il
proposito di estendere ed approfondire in futuro i dati
che ci saranno messi a disposizione da altri atenei
italiani, riteniamo che questo grafico possa essere
rappresentativo di una situazione di fatto comunemente
nota. Il dato più evidente, in particolare, è il ruolo
svolto dalla scuola nel placement post-dottorato nei
due atenei. Se nella realtà messinese, infatti, più di un
D ot to ra to in Fisica Di M e ssin a
Are a o ccup a zio n a le : Un ivers ità
7 3,3 3%
1 6,6 7%
1 0 %
S tru ttu ra ti Estero
S tru ttu ra ti I ta lia
No n S tru t tu rat i
73 ,3 3 %
2 6,67 %
S tru ttu ra ti
No n S tru ttura ti
Area o ccu p azio na le U nive rsità
To r Ve rg a ta - R o m a
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
54
dottore di ricerca su quattro trova impiego in ambito
scolastico – un dato, quest‘ultimo, che proietta la
scuola al secondo posto tra le quattro macroaree prese
in considerazione –, nella realtà romana il placement
nella scuola è quasi nullo, occupando, in percentuale,
meno di tre dottori di ricerca su cento. Il dato non
evidenzia maggiori opportunità di lavoro
geograficamente localizzate nel comprensorio
messinese-siciliano rispetto a quello romano,
considerando che parte di coloro che si dedicano
all‘insegnamento cercano e trovano la collocazione
geografica della propria professione tanto a sud quanto
al centro-nord d‘Italia. Questo significa, in altre parole,
che l‘insegnamento, come sbocco di lavoro post-
dottorato, non è un dato fortemente condizionato dal
territorio, se non per un retaggio culturale che
richiederebbe, tuttavia, una analisi alquanto diversa da
quella sviluppata in questa sede.
Il secondo dato che emerge in modo evidente è che
mentre l‘Università svolge un ruolo pressappoco
uguale nella collocazione dei due atenei, diversa è la
collocazione dei dottori di ricerca presso gli enti di
ricerca. Benché, infatti, la macroarea dei dottori di
ricerca messinesi che approdano agli enti di ricerca sia
significativa – il 15% è un dato sicuramente positivo –
non si può fare a meno di notare che il dato tendenziale
relativo a questa macroarea nell‘ateneo romano sia di
rilevanza assoluta, attestandosi intorno al 40%.
Non v‘è dubbio che altre e più ampie riflessioni
potrebbero essere sviluppate a partire dagli elementi in
nostro possesso. Mi preme tuttavia sottolineare, in
conclusione, che dati e analisi riportati in questa
indagine vanno presi in considerazione in una
prospettiva tendenziale e approssimativa, nel senso che
quelli presentati in questa relazione sono soltanto i
primi elementi di una ricerca che tende, per sua natura,
ad un‘ampia raccolta di informazioni che verrà
approfondita nel corso dei prossimi mesi. Pur essendo
parziali, tuttavia, i dati a disposizione appaiono già
significativi, a condizione, evidentemente, che vengano
declinati in una chiave di lettura volta a comprendere la
continua e rapida evoluzione del mondo del lavoro e la
necessità che l‘istituzione universitaria riesca ad avere
una sempre maggiore conoscenza e coscienza del
placement di laureati e dottori di ricerca.
Grafico F: Occupazione totale dei dottori di ricerca: un confronto
Università degli Studi di Messina Università degli Studi di Roma
Tor Vergata
Bibliografia [1] Activity Report 2010, Dottorato di Ricerca in Fisica
dell‘Università di Messina, L.Torrisi Ed. ISSN n° 2038-5889,
2011-11-25
[2] Sito WEB Università degli Studi di Roma Tor Vergata:
http://dottorati.uniroma2.it/
8 ,33 %
15 %
5 0%
26 ,67 %
U nive rs ità
Scu ol a
E nti
ri cer ca
Al tr o
14,29%
40%
42,86%
2,86%
UniversitàScuola
Enti
ricerca
Al tro
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
55
AN OVERVIEW OF RESEARCH ACTIVITIES IN THE PHYSICS PHD
COURSE
F. Caridia,b
, L. Torrisic,d
a)Facoltà di Scienze MM. FF. NN., Università di Messina, Viale F. Stagno d’Alcontres, 31 – 98166- Messina, Italy.
b)INFN-Sez. CT, Gr. Coll. di Messina, Viale F. Stagno d’Alcontres, 31 – 98166- Messina, Italy.
c)Dipartimento di Fisica, Università di Messina, Viale F. Stagno d’Alcontres, 31 – 98166 – Messina, Italy.
d)INFN-LNS, Via S. Sofia 44, 95124, Catania, Italy.
Abstract
An overview of research activities of the PhD course
in Physics of the Messina University is reported. The
research is developed mainly in the areas of matter
structure, applied, theoretical and nuclear physics.
Many different laboratories are available for PhD
students: laboratory of plasma physics; laboratory of
acoustic and dielectric spectroscopy; laboratory of
spectroscopy, biophysics and applied physics;
laboratory for studying nuclear reactions on nucleons
and nuclei; laboratory of IR and Raman spectroscopy;
nuclear physics laboratories; laboratory of low
temperature physics; laboratory of computational
physics; laboratory of microanalysis, spectroscopic
techniques and nanomaterials; laboratory of optical
spectroscopy and laboratory of spectroscopic analyses.
A particular attention is given to collaborations of
research groups and issues covered by PhD theses in
recent years.
Introduction
The Doctorate in Physics of the Messina University
has the aim to provide a satisfactory degree of
competence and professionalism in the field of
Condensed matter, Nuclear Physics, Bio-Physics and
cultural heritage and environmental Applied Physics.
The research activities are developed mainly at the
Physics Department and at the Matter Physics and
Electronic Engineering Department of Messina
University, at the National Institute of Nuclear Physics
(INFN) and at the Institute for Chemical and Physical
processes (IPCF) of Messina CNR.
Many other national and international collaborations
also give the possibility to improve the scientific
knowledge of PhD students, working in big facilities of
last generation.
Research laboratories
The laboratories of the PhD course are reported in
Table I.
Laboratory Responsible
Laboratory of plasma physics Prof. L. Torrisi
Laboratory of acoustic and dielectric
spectroscopy
Prof. M. Cutroni
Laboratory of spectroscopic
techniques, biophysics and applied
physics
Prof. S. Magazù
Laboratory for studying nuclear
reactions on nucleons and nuclei
Prof. G. Giardina
IR and Raman Spectroscopy
Laboratory
Prof. D. Majolino
Nuclear Physics Laboratories Prof. R.C. Barnà
Laboratory of low temperature physics Prof. G. Carini
Laboratory of computational physics Prof. C. Caccamo
Laboratory of microanalysis,
spectroscopic techniques and
nanomaterials
Prof. F. Neri
Laboratory of optical spectroscopy Prof. G. Mondio
Laboratory of spectroscopic analyses Prof. L. Silipigni
Tab. I: Research laboratories of the PhD course
LABORATORY OF PLASMA PHYSICS
Instrumentation: Laser Nd:YAG, 1064 nm e 532
nm, 3 ns, 0-300 mJ, mass quadrupole spectrometer
with energy filter HIDEN EQP 300, classic mass
quadrupole spectrometer BALZERS PRISMA 300,
Langmuir probe, optical spectroscope, Faraday cup for
time-of-flight measurements, optics and vacuum
systems, detection electronics (Fig. 1).
Research activity: the experimental setup consists
in a Nd:Yag laser, operating at 1064 and 532 nm, with
a pulse width of 3 ns and maximum energy of 300 mJ.
The beam is focalized through a optical lens at a
distance of 50 cm, in order to have, in the solid target,
inside a vacuum chamber, a laser spot of around 1 mm2
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
56
at pressure of the order of 10-6
mbar. The interaction of
the beam with the target produces an ablation and
consequently plasma generation [1].
Applications: diagnostic of plasma laser-generated,
deposition of thin films (Pulsed Laser Deposition),
laser welding, nuclear physics (Laser Ion Source, D-D
fusion), cultural heritage applications (compounds,
isotopic ratios, surface patina analysis).
Fig. 1: Experimental setup of the Laboratory of
Plasma Physics of Messina.
Collaborations: INFN-LNS, ASCR PALS Lab.,
Institute of Plasma Physics and Laser Microfusion,
University of Pisa, Salento, Roma Tor Vergata and
Milano-Bicocca, CELIA (Centre Lasers Intenses et
Applications), MT-LAB, Bruno Kessler foundation.
LABORATORY OF ACOUSTIC AND
DIELECTRIC SPECTROSCOPY
Instrumentation: setup for ultrasound analysis
(MATEC TB1000 e MATEC 6000), setup for wide
band measurements, wave guides.
Research activity: condensed states physics. It
principally concerns problems of disorderly systems
behavior. Different techniques, structural and
dynamics, are employed: ultrasound (kHz-MHz), fully
employed in physics and engineering for non-
destroying tests (NDT), dielectric spectroscopy
(systems for wide band measurements 10-3
Hz - 2
GHz), to measure the real part ε '(ω), and the imaginary
part ε (ω), of the complex permittivity of a material
(solid, liquid) in a wide range of frequency 10-3
Hz-2
GHz, at temperatures between 450 °K and 3 °K using
only one sample. Wave guides (8.2 GHz – 40 GHz) are
also employed for measurements of the complex
permittivity at a frequency in the microwave range
with transmission lines at rectangular wave guides and
at temperatures between the room value and 10 °K [2].
Collaborations: University of Pavia, CNR–ITC,
Arizona State University, Texas Tech University,
Universidad Autonoma de Madrid, Chalmers
University of Technology.
LABORATORY OF SPECTROSCOPIC
TECHNIQUES, BIOPHYSICS AND APPLIED
PHYSICS
Instrumentation: experimental setup for static and
quasi-elastic scattering measurements, infrared
spectrometer for biophysics measurements.
Research activity: the laboratory disposes of top-
table devices (spectroscopic techniques of elastic type,
quasi-elastic and inelastic of electromagnetic radiation)
useful to the dimensional and morphologic, qualitative,
structural, dynamic and thermodynamic
characterization of a wide class of materials of
physical, biotechnological and industrial interest. The
laboratory also disposes of instrumentation for
measurements and analysis for ambient studies
(electromagnetic pollution, air pollution, …) [3].
Applications: investigations about the mechanisms
of bio-protection, micro-emulsion, gel micro-emulsion,
innovative materials, physical and chemical properties
of macro-molecular and polymeric systems of
biological interest and optimization of physical devices
for energetic and industrial fields.
Collaborations: LDSMM (CNRS), CEMHTI
(CNRS), Institute Laue Langevin, Rutherford Appleton
Laboratory, BENSC, ESRF, Soleil, Sanofi-Aventis,
Dompè, Labplants, Cosmetic Valley, ESA, Cape Town
University.
LABORATORY FOR STUDYING NUCLEAR
REACTIONS ON NUCLEONS AND NUCLEI
Research activity: study of barionic resonances by
mesons photoproduction at the facility ELSA in Bonn
(Germany) within the international cooperation
BGOOD. The Messina group in BGOOD has the tasks
of experimental setup simulations (activity carried out
in site) and of hardware and software administration of
hydrogen and deuterium cryogenic liquid target
(activity carried out in site and at ELSA).
Study of reactions induced by heavy ions for the
production of superheavy elements. The experimental
activity is carried out at China Institute of Atomic
Energy (CIAE) in Beijing (China). Activity of
calculation, experimental data analysis and
interpretation is carried out in site.
Study of Bremssthralung radiation emitted during
spontaneous fission processes and alpha decay of
heavy elements [4].
Collaborations: Institute for Nuclear Studies,
Division of Nuclear and Particle Physics, Helmholtz-
Institut fuer Strahlen und Kernphysik, Institut fuer
Kernphysik, Institut fur Experimentelle Kernphysik,
Institute for Theoretical and Experimental Physics,
Institute of Physics Jagiellonian University, Ivane
Javakhishvili State University of Tbilisi, Joint Institute
for Nuclear Research,
National Central University Jhongli, University of
Bonn, Physikalisches Institut University of Bonn,
MQS IC
Laser
Vacuum chamber
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
57
Helmholtz Institut f¨ur Strahlen- und Kernphysik,
Petersburg Nuclear Physics Instute, University Roma
Tor Vergata and INFN Roma2, INFN Roma1, INFN
Laboratori Nazionali di Frascati, University of Pavia
and INFN Pavia, University of Edinburgh, University
of Kharkov, University of Moscow, Bogoliubov
Laboratory for Theoretical Physics of JINR, Flerov
Laboratory for Nuclear Reaction of JINR, Institute for
Nuclear Research of NASU, Lomonosov Moscow
State University.
IR AND RAMAN SPECTROSCOPY
LABORATORY
Instrumentation: Interferometry Spectrometer
BOMEM DA8 for IR absorption measurements in
Fourier Transform (FT-IR), for measurements in
Attenuate Total Reflectivity (ATR), for FT-IR micro-
spectroscopy and Raman scattering measurements in
Fourier Transform.
Pulverizer, hydraulic press, digital balance and
electric stirrer with temperature control (50 °C – 350
°C) to prepare and store samples.
Portable XRF Analyzer ―Alpha 4000‖ Innov-
Xsystems for X-Ray Fluorescence measurements
(XRF).
Research activity: complete characterization of
dynamic and structural and/or compositional properties
of matter, both in liquid state and solid state by the use
of complementary spectroscopic tecniques. Thanks to
the not invasivity of the techniques, these
spectroscopic methodology can surely find a large and
natural application in a lot of fields nowadays
fundamental [5].
Applications: archeometry, characterization, storage
and recover of cultural heritage, biomedicine and/or
biophysics.
Collaborations: BENSC (BErlin Neutron Scattering
Center), ESRF (European Synchrotron Radiation
Facility), ILL (Institut Laue-Langevin Facility), ISIS
Rutherford-Appleton Laboratory Oxford, LLB
(Laboratoire Lèon Brillouin).
Nuclear physics laboratories
RADIATION PROCESSING LABORATORY
Instrumentation: Linac of electrons of 5 MeV
(nominal energy 5 MeV, peak current 1-200 mA, pulse
time 3 sec, peak power 1 MW, power 1 kW,
repetition frequency 1-300Hz, frequency RF 2.997
GHz, No. accelerating cavities 9, no magnetic lens,
beam diameter 4 mm).
Applications: creation of new hydrogels,
improvement of mechanic properties of UHMWPE and
wood properties by impregnation and irradiation, study
of the gas diffusion in irradiated Black PE, filament
winding, dejection of mycotoxins of food flour,
substances released during the irradiation of different
types of PE, radiative treatment of adhesive joints for
structural-type applications in the aerospace and
automobile field, recognizing of materials by non
destructive testing techniques, calibrations to recognize
irradiated foods, development of new dosimeters for
radiation processing and project of accelerating
systems for industries interested [6].
INFORMATICS LABORATORY
Instrumentation: cluster of parallel computation (6
double-processors + file server). Protocols of Parallel
Computation: PVM (Parallel Virtual Machine), MPI
(Message Passing Interface).
Research activity: Monte Carlo Simulation of
radiation processing treatments by MCNP-4C2 code
(Monte Carlo N Particle, version 4C2) and data
analysis relative to experiments carried out with the
CHIMERA multidetector (LNS).
APPLIED NUCLEAR PHYSICS LABORATORY
Instrumentation: lecture systems for optical
dosimeters (Gafchromic) and rivelation system of
cooling Ge(Li) + spectrometer α.
Research activity: dose and dose-rate
measurements, environmental radioactivity
measurements (Radon measurements on samples of
aspirated air on porous filters, radioactivity
measurements in drinking water and on building
materials).
Collaborations: INFN, Institute for Physics and
Nuclear Engineering, Institute of Physics, University of
Silesia, Institute of Physics, Jagellonian University,
Institute de Physique Nucleaire, IN2P3-CNRS and
Université Paris-Sud Orsay, LPC, ENSI Caen and
Université de Caen, Saha Institute of Nuclear Physics,
Kolkata, GANIL, CEA, IN2P3-CNRS Caen, Institute
of Nuclear Physics Cracow, Institute of Modern
Physics Lanzhou, Institute of Experimental Physics
Warsaw University.
LABORATORY OF LOW TEMPERATURE
PHYSICS
Experimental techniques: mechanical spectroscopy
and ultrasounds; low and high temperature calorimetry;
Brillouin and Raman spectroscopy; low temperature
techniques; high magnetic fields; preparation of glasses
and polymers.
Topics: influence of the disordered topology on the
physical properties of materials; glass transition; low
energy excitations; vibrational and relaxation
dynamics.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
58
Research activity: solid state physics. Materials:
glasses and polymers [7]. Collaborations: Institut für Festkörperforschung,
Forschungszentrum Jülich, IPCF-CNR Messina,
Institute of Macromolecular Chemistry, National
Academy of Sciences of Ukraine, IMEM-CNR Parma,
Institute Laue-Langevin Grenoble, Department of
Chemistry and Department of Physics and Astronomy,
University of Tennessee.
LABORATORY OF COMPUTATIONAL
PHYSICS
Instrumentation: Parallel Cluster made of 10 PC
Pentium R Dual Core E5300 @ 2.60GHz 10Gb RAM,
4Tb, at the Department of Physics; parallel cluster
made of 20 knots equipped with 4 Dual Core AMD
Opteron Processor 280 and 4Gb RAM for each one (ex
TriGRID project), allocated at the Center for Electronic
Computing ―A. Villari‖; access to grid managed by the
Consorzio Cometa (http://www.consorzio.cometa.it)
among the project PI2S2 (http://www.pi2s2.it).
Research activity: Statistical mechanical study of
microscopic properties, structural and thermodynamic
properties (including the phase equilibria) of simple
and complex fluids. Integral theory of a fluid state for
single site or several sites of interaction (Ornstein-
Zernike equation, RISM Theory - Reference
Interaction Site Model). Monte Carlo simulation
methods and dynamic molecular models applied to
both monatomic and molecular fluids, either pure or
mixed.
Collaborations: Laboratoire de Physique des
Milieux Denses, Université de Metz, France, School of
Physics University of Kwazulu-Nathal,
Pietermaritzburg, South Africa, CNR-IPCF Messina,
University ―La Sapienza‖ Rome.
Laboratory of microanalysis, spectroscopic
techniques and nanomaterials
LABORATORY OF MICROANALYSIS
Instrumentation: microanalysis, imaging and depth
profiling using XPS, high yield (tens of analysis/day),
visual control of positioning for the microanalysis,
argon ion gun for removing surface layers, electron
gun to reduce the effects of electrical charging of
insulating materials, software and libraries for the
automatic recognition of the chemical composition.
Automated setup for measuring dc electrical
conductivity as a function of temperature (100-550 °K)
using the volt-amperometric method for voltage or
constant current. The system is equipped with a
cryostat cooled with liquid nitrogen with optical
windows, to measure photoconductivity.
Measurements of profilometry and roughness on
surfaces by scanning with lateral resolution of about 10
microns, and vertically up to 10 Å (Profilometer KLA-
Tencor Alpha Step 500).
Research activity: physical-chemical diagnostics,
morphological, structural and electrical engineering,
micro- and nano-scale solid surfaces and thin film
multilayer structures. By means of X-ray
photoemission spectroscopy (XPS), the surface
compositional mapping on the micrometer scale and
the effects due to the overlapping layers of different
materials are analyzed, through the depth profile
analysis. The study of compositional and structural
properties of thin films of SRO (Silicon Rich Oxide)
and silicon oxy-nitride devices for applications in
power MOSFETs and thin-film photovoltaic converters
was recently approached [8].
Collaborations: ANM Research, C.S.R.A.F.A,
Messina.
LABORATORY OF SPECTROSCOPIC
TECHNIQUES
Instrumentation: Raman spectroscopy system.
Back-scattering configuration, laser sources: multi-line
Argon, diode pumped Nd:YAG (second harmonic),
He-Ne. Analyzer: flat field Triax 320 monochromator
coupled with a BX 40 Olympus microscope and
equipped with gratings of 1800 and 600 lines / mm
holographic filter to eliminate the elastic scattering
component. Detector: Diode matrix CCD 1024 × 128,
cooled with liquid nitrogen. Mapping micrometer with
lateral resolution 1X1 (2 μm) using automated XY
translation. Setup for measurements on colloidal
solutions using a 10X lens focal length.
Non-linear optical spectroscopy (Z-scan technique).
Measurement system in the open and closed
configuration of a pulsed laser beam transmission
(Nd:YAG, 5 nsec), focused by a radiometric system
with two sensors and the scanning engine of the sample
along the optical axis.
Research activity: physical-chemical
characterization of bonding structures of materials in
the form of thin films and colloidal solutions of
nanoparticles: thin films of SRO (Silicon Rich Oxide),
silicon-carbon alloys and carbon-based nanostructured
systems, colloidal solutions of nanoparticles of metallic
oxides and metallic nanoparticles for applications
SERS (Surface Enhanced Raman Spectroscopy).
Analysis of nonlinear optical response of colloidal
systems of nanoparticles-based carbon and silicon:
study of the absorption coefficient and refractive index
as a function of laser pulse repetition rate,
concentration and solvent.
Collaborations: ANM Research, C.S.R.A.F.A,
Messina.
Laboratory of nanomaterials
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
59
Instrumentation: Nd-YAG laser pulse until the
fourth harmonic (266 nm), power adjustable up to 180
mJ (second harmonic), pulse duration 5 ns, repetition
up to 20 Hz, optical beam focusing, handling and
control of the metal target submerged in liquid (system
for laser ablation in liquids). System for spraying
deposition of thin layers of colloidal solutions: the
technique of spraying by automated airbrush is a
methodology used for the transfer of nanoparticles in
colloidal phase on surfaces of various kinds (even
flexible). The system consists of a compressed gas
atomizer with interchangeable nozzles of various sizes.
The nozzle is placed on a medium which ensures a
movement for a uniform distribution of nanoparticles
on the surface to be coated. The jet is directed into a
deposition chamber that houses a sample holder heated
to a temperature higher than the evaporation of the
solvent. A system for the removal of moisture in the
deposition chamber is also provided.
Research activity: synthesis, laser ablation in
liquids, and characterization of nanostructured metal
oxides for the production of gas sensors and
applications of metal nanoparticles for SERS (Surface
Enhanced Raman Spectroscopy).
Collaborations: ANM Research, C.S.R.A.F.A,
Messina.
LABORATORY OF OPTICAL SPECTROSCOPY
Instrumentation: PE 750 UV-Vis-Nir Perkin Elmer
(200 – 3300 nm), Lambda 2 UV-VIS-Nir Perkin-Elmer
(200 – 1100 nm), FT-IR (Spectrum 100) Perkin Elmer
(7800-370 cm-1
) spectrophotometers; FluoroMax – 2
Jobin Ivon (200-900 nm) spectrophotofluorimeter;
optical microscope.
Research activity: optical spectrophotometry (UV-
VIS-NIR). Measurements of absorption of
electromagnetic radiation in the UV-VIS range allow
to make a qualitative analysis of a given material. The
profile of an absorption spectrum depends on various
parameters such as the chemical and aggregation state
of the analyzed sample. In addition, the absorption at a
given wavelength depends on the nature and
concentration of the analyte [9].
Collaborations: ST Microelectronics, Catania, CNR
Messina, RIS Messina.
LABORATORY OF SPECTROSCOPIC
ANALYSES
Instrumentation: System for dielectric and
electrical transport measurements (RLC HP4284A
shunt, RMC LTS-LN2-VT cryostat, vacuum system (~
10-6
torr), temperature control device Lake Shore 330,
Keithley 236 unit, pc).
Research activity: study of electrical transport and
dielectric properties of organic-inorganic hybrid
multifunctional materials films and powders consisting
of intercalation (nanocomposite) prepared by our
research group. The electronic properties of these
materials are also studied, using the photoelectronic
spectrometer, dual anode Mg/Al K and the optical
properties by means of spectrophotometers available in
the laboratory of optical spectroscopy [10].
Collaborations: IPCF-CNR Messina, CNR Napoli.
Conclusions
During the last five years a number of twenty PhD in
physics were formed at the Messina University.
The experience accumulated during the years of
doctoral and skills acquired allow them to aspire to
scientific careers in universities, institutes of higher
education, in research institutions and national (CNR,
INFN, ENEA, ENI, etc..) and International
Laboratories, with a special screening in Europe. The
professionalism of a PhD doctor allows also the
inclusion in any facility operating in areas requiring
advanced professional skills through computer
programming and simulation models of complex
processes and teaching in secondary schools of
physics, mathematics, electronic and information
technology.
References
[1] L. Torrisi, F. Caridi, L. Giuffrida, Nucl. Instr. And
Meth. B, 268 (2010) 2285-2291;
[2] A. Mandanici; M. Cutroni, R. Rickert, Journal of
Non-Crystalline Solids, 357 (2) 264-266 (2011);
[3] S. Magazù, F. Migliardo, A. Benedetto, The
Journal of Physical Chemistry B, 115 (24) 7736-
7743 (2011);
[4] A.K. Nasirov, G. Mandaglio, M. Manganaro, A.I.
Muminov, G. Fazio, G. Giardina, Physics Letters
B, 686 (1) 72-77 (2010);
[5] G. Barone, V. Crupi, F. Longo, D. Majolino, P.
Mazzoleni, V. Venuti, Journal of Molecular
Structure, 993 (1-3) (2011);
[6] Auditore L., Barna R.C., Emanuele U., Loria D.,
Trifiro A., Trimarchi M., Nucl. Instr. and Meth. B,
266 (10) 2138-2141 (2008);
[7] G. Carini, G. Tripodo, L. Borjesson, Materials
Science & Engineering A, 521-522 247-250 (2009);
[8] E. Fazio, F. Neri, S. Patanè, L. D‘Urso, G.
Compagnini, Carbon, 49 (1) 306-310 (2011);
[9] A.M. Mezzasalma, G. Mondio, T. Serafino, F.
Caridi, L. Torrisi, Appl. Surf. Sci., 255 (7) 4123-
4128 (2009);
[10] L. Silipigni, L. Schirò, L. Monsù Scolaro, G. De
Luca, G. Salvato, Appl. Surf. Sci., 257 (24) 10888-
10892 (2011).
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
61
ENHANCED OPTICAL FIELDS FOR AGGREGATION OF METAL
NANOANTENNAS AND LABEL FREE HIGHLY SENSITIVE DETECTION
OF BIOMOLECULES
B. Fazio
a,*, C. D‘Andrea
a,b, V. Villari
a, N. Micali
a, O. Maragò
a, G. Calogero
a and P.G. Gucciardi
a
a) CNR – Istituto Processi Chimico-Fisici, viale F. Stagno D’Alcontres 37, 98158 Messina, Italy
* Corresponding author, e-mail: fazio@me.cnr.it
b)Dottorato in Fisica dell’Università di Messina, Dip.to di Fisica della Materia e Ingegneria Elettronica,
viale F. Stagno D’Alcontres, 98158 S. Agata-Messina, Italy
Abstract
Aggregated metal nanostructures are characterized by
strongly intense electromagnetic fields localized in the
cavities region, referred as ―hot spots‖, allowing for
high sensitive vibrational spectroscopy. We report on
the implementation of a laser induced Surface-
Enhanced Raman Scattering sensor in liquid
environment by controlled aggregation of gold
nanorods dispersed in solution obtained through an
interplay between thermal and radiation pressure
effects. The creation of highly efficient hot spot
regions enables the Raman detection of proteins
dissolved in buffer solution at low concentration (down
to 10-7
M) with an estimated enhancement factor of
105. This methodology paves the way to a new
generation lab-on-chip sensors that implies user-
friendly experimental set up allowing for highly
sensitive vibrational spectroscopy of biomolecules in
their natural habitat and getting over the drawback of
the standard methods based on the difficulty to
manipulate metal nanostructures or realize active
substrates that experience a highly efficient SERS.
Introduction
The discovery of Surface-Enhanced Raman
Scattering (SERS) phenomena and single molecule
sensitivity [1-5], due to the unique electronic and
optical properties of metal nanoparticles, opened the
doors to promising applications in material science and
optical biosensors.
SERS from isolated metal nanostructures is usually
much weaker compared to what is observed on
aggregates due to the strong field enhancement
occurring in the gap regions (hot spots) between
adjacent nanoobjects [2-5]. A controlled creation of hot
spots in liquid, the natural habitat of biomolecules, is a
challenge in which optical forces play an important
role. Optical trapping (OT), manipulation and
deposition of metal nanostructures, gold and silver,
has been at the center of an intense research [6-9].
Here we show how the simultaneous occurrence of
optical, mechanical and thermal effects, promotes
aggregation of already formed gold nanorods staying in
a colloidal suspension with the consequent creation of
hot spot regions where biomolecules experience high
field enhancement fundamental for their label free
detection at submicromolar concentration. We validate
the SERS biosensor efficiency by detecting
biomolecules as Bovine Serum Albumin (BSA),
Phenylalanine (Phe), Lysozyme (Lyz) and a protein not
yet well known from a spectroscopical point of view,
but of a great biomedical interest, the Manganese
Superoxide Dismutase (MnSOD). Indeed, the MnSOD
is considered a valid pathological biomarker, due to its
levels in the plasma that are significantly higher in
patients with ovarian carcinoma.
Materials and methods
Materials. Commercial gold nanorods (35x90 nm) are
purchased from Nanopartz. They come in a DI water at
a concentration of 0.05 mg/ml; the solution contains
<0.1% ascorbic acid and <0.1%
Cetyltrimethylammonium bromide (CTAB) surfactant
capping preventing spontaneous re-aggregation, and
have a positive -potential (+40 mV). The Bovine
Serum Albumin buffered solutions at various
concentrations (in the range between 10-3
M and 10-
7M) are prepared by mixing the suitable amount of
BSA lyophilized powder (Sigma-Aldrich) with a 200
mM of Phosphate Buffer Solution (pH 7.2) obtained
with Na2HPO4(14.94 g) and NaH2PO4 (5,063 g)
dissolved in 200mL of DIwater. Then, the gold
nanorods solution is added to the prepared mixture
with a ratio of 1:7 v/v. An amount of 75 l of BSA
and NRs solution was put inside a typical glass cell
used for optical trapping experiments. Following the
same procedures we prepared analogous solutions
containing gold nanorods and, respectively, Lyz at 10-
6M, MnSOD at 10
-4M and Phe at 10
-3M in PBS.
Setup. We performed the SERS experiment using a
Raman Micro-Spectrometer (LabRam HR800 - Horiba
Jobin Yvon) coupled to the 632.8 nm line of a He-Ne
laser; the beam (P = 6.3 mW) was focused on a 500 nm
diameter spot in the liquid, close to the bottom of the
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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cell, by a 100X microscope objective (Olympus,
NA=0.95) a droplet of the BSA and NRs solution is put
inside a glass cell (a model typically used for optical
trapping experiments) and placed under a Raman
Micro-Spectrometer (LabRam HR800 - Horiba Jobin
Yvon) coupled to the 632.8 nm line of a He-Ne laser.
The spectrometer was equipped with a Peltier cooled
CCD array (HJY-Synapse) as detector. The instrument
was also employed to collect the extinction spectrum of
the aggregate of gold NRs, by using a Xe lamp as
white light source.
Figure 1: (a) Sketch of the experiment and of the
formed aggregate. (b) Absorption spectrum of the gold
nanorods solution (blue line) compared to the
extinction spectrum of the photo-induced aggregate
(brown line).
Results and discussion
By manually changing the fine focus inside the
solution and setting it at the bottom of the cell close to
the rim, the intercepted gold nanorods are mechanically
constrained in a confined region; the aggregation
process is activated in some seconds; in figure 1.a a
sketch of the experimental configuration and the
aggregate formation. Due to the slightly blue shifted
excitation with respect to their LSP resonance, the gold
nanorods are subjected to both a scattering force and a
repulsive gradient force, so that they are not trapped in
the laser focus but rather strongly pushed towards the
bottom of the sample cell along the optical axis. On
the cell surface they aggregate for photoinduced
thermal effect [9,10].
The extinction spectrum of the formed aggregate
(figure 1,b), captured in situ, shows a broad band
extinction feature, ranging between 420 and 900 nm
and peaked at 770 nm, that dominates; it is suitable to
underline that the 632.8 nm of laser source, used as
SERS probe, falls whithin the localized surface
plasmon resonance of the aggregate, while it falls
outside of the single rods plasmonic absorption
features (figure 1,b blue line) at λLSP = 687 nm and λLSP
= 527 nm, along their long and short axes respectively
[11].
The relatively high energy density (~ 25 mW/µm2) in
the focal spot and the quasi resonant laser excitation of
the LSPs modes causes a not negligible light
absorption by the NPs which is partially converted into
heat. By Stokes/Anti-Stokes Raman measurements we
have estimated a temperature of about 60°C in the
irradiated zone after 10 minutes of laser focusing. At
this temperatures thermally induced structural
rearrangement of gold nanorods in micelles capping
has been observed [12].
Depolarized Light Scattering (DLS) measurements,
here not shown, confirm that a thermal re-organization
of the rods into small clusters takes place in the
investigated solution at temperature as low as 60°C.
Indeed, the mean hydrodynamic radius of about 65 nm,
detected at room temperature and due to gold rods with
a shell of BSA, likely stabilized by electrostatic
interaction between the positively charged capping
agent of the rods and the negative charge of BSA,
becomes 100 nm for the gold/BSA aggregates at 60°C.
Figure 2: (a) SERS of buffered BSA molecules at 0.1
mM (black line), 1 M (red line) and 0.1 M (blue
line) . (b) Raman spectrum of buffered BSA solution at
0.1 mM without nanorods induced aggregation.
This increment of the mean size is due to thermal
aggregation between gold rods mediated by BSA, that
at this temperature is known to form small oligomers.
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In figure 2 is shown the strong SERS signal of BSA
molecules staying in the aggregates proximity,
compared to the Raman signal of the same solution in
absence of aggregates formation. We estimated a SERS
enhancement factor of 2x105 by the ratio between the
intensity of the SERS feature of the phenylalanine ring
breathing at 1004 cm-1
obtained for the buffered
solution of BSA at concentration of 10-7
M and the
same Raman feature collected for a buffered solution
of BSA 10-3
M without gold nanorods addition. BSA at
10-3
M corresponds to the concentration limit for the
Raman detection in our experiment.
Under the same experimental conditions (time=10s, 4
accumulations, after a NRs aggregation time of 30s)
the intensities of the SERS spectra are not depending
on the BSA concentration. This occurrence confirms
that what we reveal is SERS from hot spot region and
suggests us that tenths of micromolar concentration of
protein is not a detection limit for our experiment.
However, when a concentration of 10-8
M of BSA in
PBS solution is added to the same concentration of
NRs solution previously used, not stable aggregates are
formed and we hardly collect only SERS spectra of
the CTAB surfactant.
In this latter case any BSA mediation and stabilization
process occurs for aggregates formation, owing to the
protein negligible amount that don‘t saturate the rods
quantity; as a consequence, only a transient NRs
aggregation due to the optical forces is experienced and
immediately disrupted by the repulsive electrostatic
action of the surfactant layer.
The temporal dynamics of the photothermal creation of
the hot spots can be followed by acquiring consecutive
SERS spectra (figure 3a) and monitoring the temporal
increase of the intensity of the protein spectral
signatures. We observe a preferential increment of the
features attributed to the aromatic residues in the
structure (Phe, Tyr, Trp), due to the intercalation of the
hydrophobic side chain into the CTAB layer. The high
enhancement of the 1395cm-1
COO-symmetric
stretching is due to the strong electrostatic interaction
with the surfactant bilayer. A similar behavior has been
observed by Kaminska and coworker in the interaction
between bovine pancreatic trypsin inhibitor (BPTI) and
CTAB-protected gold nanoparticles deposited on
functionalized silicon surface [13,14].
Figure 3: Consecutive SERS spectra of BSA in PBS
solution and gold nanorods (a). Trend vs time of some
protein spectral features (b).
The functionality of the SERS biosensor obtained by
photoinduced aggregation of gold nanorods has been
validated for many molecules of biological interest. In
figure 4.a,b,c the SERS spectra of lysozyme protein,
Phenylalanine amminoacid and Manganese Superoxide
Dismutase, compared to the Raman signal of the
respective powders are shown [15].
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
64
Figure 4: SERS of buffered biomolecules solutions
(blue lines) compared to Raman spectra of the
respective powder and to the Raman spectra of the
same solution in absence of gold aggregates: (a)
Lysozyme in PBS at 1 M, (b) Phenylalanine in PBS at
1 mM and (c) Manganese Superoxide Dismutase at
0.1 mM.
Conclusions
In summary, we implemented a SERS biosensor based
on photothermally aggregated gold nanorods, operating
in liquid environment. This in situ aggregation process
has been applied for the Raman detection of Bovine
Serum Albumin (BSA) molecules in Phosphate Buffer
Solution (PBS) at concentration down to 10-7
M. The
method has been successfully validated for the SERS
detection other molecules of biological interest in their
natural habitat, as Phe, Lyz and MnSOD, the latter
being a precious biomarker in medical diagnosis.
Acknowledgments
We acknowledge funding from the EU-FP7-
NANOANTENNA project GA 241818 ―Development
of a high sensitive and specific nanobiosensor based on
surface enhanced vibrational spectroscopy‖ and the
PRIN 2008 project 2008J858Y7_004 ―Plasmonics in
self-assembled nanoparticles / Surface Enhanced
Raman Spectroscopy on self-assembled metallic
nanoparticles.‖
References
[1] M. Moskovitz, Rev. Mod.Phys. 1985, 57, 783.
[2] S. Nie and S. R. Emory, Science 275 (1997) 1102.
[3] K. Kneipp et al., Chemical Physics 247 (1999) 155. [4] K. Kneipp, M. Moskovits and H. Kneipp, Surface Enhanced
Raman Scattering; Springer: New York, 2006.
[5] E. Le Ru, P. Etchegoin, Principles of Surface Enhanced
Raman Spectroscopy; Elsevier: Amsterdam, 2009.
[6] F.Svedberg et al., Nano Lett., 6 (2006) 2639.
[7] F. Svedberg et al., Faraday Discuss., 132 (2006) 35
[8] L. Tong, Lab Chip, 9 ( 2009) 193. [9] M. J. Guffey and N. F. Scherer, Nano Lett., 10 (2010) 4302
[10] M. J. Guffey and N. F. Scherer, Proc. of SPIE, Optical
Trapping and Optical Micromanipulation VII, edited by Kishan Dholakia, Gabriel C. Spalding (2010) Vol. 7762.
[11] P. H. Jones et al., ACS Nano 3 (2009) 3077.
[12] M.B. Mohamed, J. Phys. Chem B., 102 (1998) 9370 [13] A. Kaminska et al., Phys Chem Chem Phys 10 (2008) 4172.
[14] A. Kaminska et al., Journal Raman Spect 41 (2009) 130.
[15] B. Fazio, C. D‘Andrea, V. Villari, N. Micali, O. Maragò, M.A. Iatì, G. Calogero, P.G. Gucciardi, in preparation.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
65
MISSING RESONANCES AT THE BGO-OD EXPERIMENT
F. Curciarelloa,b,*
, V. De Leoa,b
, G. Mandaglioa,b
, M. Romaniuka,b,c
, G. Giardinaa,b
a)Dipartimento di Fisica, Università di Messina, I-98166, Messina, Italy
b) INFN-Sezione Catania, I-95123 ,Catania , Italy
c)Institute for Nuclear Research, National Academy of Science of Ukraine, Kiev, 03680, Ukraine
*Corresponding author, e-mail: fcurciarello@unime.it
Abstract
The excited states of nucleons are mostly treated in
the framework of the so-called ―constituent quark
model‖. This model has been very successful in
describing mesons and baryons into the well known
multiplet structures and in the prediction of the
hadronic excitation spectrum by few parameters.
However there are some problems concerning the
description of the observed baryon resonance spectrum
by the constituent quark model. One problem is due to
the so-called ―missing resonances‖: much more excited
states of the nucleon are predicted by the model than
the ones have been observed in experiments. It is
unknown if this mismatch is caused by experimental
limits or by the models used to describe the nature of
quarks bonds inside nucleons. Indeed the choice of the
theoretical model is of basic importance to fix the
effective degrees of freedom of the constituent quarks
and therefore the number of possible excited states of
nucleon. For this reason other quark models have been
proposed as the ―di-quark‖ model and the ―flux-tubes‖
model. The only way to establish the proper effective
degrees of freedom is to test the theoretical predictions
with experiment[1-2-3]. In the present paper will be
presented the specific program of the BGO-OD
experiment at ELSA of Bonn in the missing resonances
research. The international experiment BGO-OD
(INFN-MAMBO experiment) consists of a 4π-
electromagnetic calorimeter, different charged sensible
detectors for tracking particles, an open dipole
spectrometer for charged particles and momentum
reconstruction.
That experiment, thanks to the high photon
luminosity (107s) of energy up to 3.2 GeV produced by
electron bremsstrahlung of the ELSA cyclotron,
represents a new experimental information source
devoted to investigation of the ―missing resonances‖
puzzle.
Introduction
The availability over the last decade of high duty-
cycle accelerators coupled with the use of large solid-
angle detectors yielded a wealth of experimental
information in the field of the photo- and
electroproduction of mesons from the nucleons. The
attempt is to extract, from photoproduction, the
electromagnetic couplings and furthermore the
hadronic properties of the excited nucleon states that
cannot be accessed via pion scattering, either because
the resonances largely overlap, or because of a weak
coupling to the single pion-nucleon channel. The
energy scale which is typical of the nucleon and its
resonances is the low energy regime where a
perturbative approach of the QCD theory is not
possible because of the strong coupling constant
becomes large. This situation offers both a challenge
and a chance: we do want to understand the physics
laws governing the bilding blocks of the matter at low
energies, in the regime where we encounter them in the
nature, on the other hands is obvious that the complex
many-body system ―nucleon‖ offers the ideal testing
ground for concepts of the strong interaction in the
non-perturbative regime. Therefore the most important
step toward the understanding of the nucleon structure
is the identification of the effective degrees of freedom
which naturally must reflect the internal symmetries of
the underlying fundamental interaction.
This step is attempted in the framework of the
constituent quark model[4-5-6] which have
contributed
Fig. 1 Effective degrees of freedom in quark
models: three equivalent constituent quarks,
quark-diquark structure, quark and flux tubes
substantially to our understanding of the strong
interaction.
The classification of the mesons and baryons in the
well known multiplet structures as derived from the
symmetry, and the description of the hadronic
excitation spectrum with only few fitting parameters
were striking success of this model. Most of the models
start from three equivalent constituent quarks in a
collective potential . Here the quarks are not point-like
but have electric and strong form factors. The potential
is generated by a confining interaction, for example in
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
66
the flux tubes picture, and the quarks interact via a
short range residual interaction. This fine-structure
interaction, usually taken as color magnetic dipole-
dipole interaction mediated via one-gluon-exchange
(OGE) is responsible for the spin-spin and spin-orbit
terms. However, alternative models were developed.
Indeed, models have been proposed that are based on a
different number of degrees of freedom (see fig.1). One
group of models describes the nucleon structure in term
of a quark-diquark (q-q2) cluster[7], if the diquark is
sufficiently strongly bound, low lying excitations of the
nucleon will not include excitation of the diquark.
Therefore, these models predict a fewer low-lying
states of the nucleon than the conventional quark
models. On the other hand other models predict an
increased number of excitation states with respect the
usual constituent quark model[8-9]. The choice of the
theoretical model to describe nucleon structure is of
crucial importance because the number of excited
states with defined quantum number (baryon
resonances) follows directly from the number of
effective degrees of freedom of quarks inside nucleon.
Consequently a comparison of the experimentally
excitation spectrum to model predictions can allow us
to determine the correct number of degrees of freedom
and so to understand the nature of quark bonds and its
interaction inside the nucleon. However, from an
experimental point of view the situation is quite
different from atomic and nuclear physic. The
dominant decay channel of a nucleon resonance is the
hadronic decay via emission of mesons (see fig. 2) .
Thus, the lifetimes of the excited states are typical of
the strong interaction (η~10-24
s) with corresponding
widths of few 100 MeV. The spacing of the resonances
is often no more than a few 10 MeV so the overlap is
very large, this makes difficult to identify and
investigate individual states.
Fig.2 Representation of a photoproduction of
meson through an intermediate state of nucleon
resonance of defined isospin I and angular
momentum J.
The most widely used reactions for the study of
nucleon resonances use beams of long-lived mesons.
However the exclusive use of pion induced reactions
would bias the data base for resonances coupling
weakly to the Nπ channel. Indeed, a comparison of
excitation spectrum predicted by modern quark models
to experimentally established set of nucleon resonances
results in the problem of ―missing resonances‖: many
more states are predicted than have been observed. It
is unknown if this evidence is related to an inept
determination of effective degrees-of-freedom in the
theoretical models or if it is an experimental limit. One
hypothesis of this mismatch is the decoupling of many
resonances from the partial wave analysis of pion
scattering. This resonances can be found when other
initial and/or final states are investigated. In fact, recent
quark models predict a number of unobserved
resonances to have large decay branching ratios for the
emission of mesons other than pions. To observe this
states, nucleon should be excited by scattering of
respective mesons. However, most of them are short
lived so the preparation of secondary beams becomes
impossible. The use of induced reactions by
electromagnetic interaction offers an alternative. The
progress made in accelerator and detector technology
during the last fifteen years has considerably enhanced
our possibility to investigate the nucleon with different
probes. In particular, the new generation of electron
accelerators, like ELSA in Bonn, are equipped with
tagged photon facilities and state-of-art detector
systems.
Fig.3 Overview of the ELSA facility in Bonn
which produce a photon beam up to 3.2 GeV
with the bremsstrahlung technique.
At ELSA facility the tagged high energy photon
beam is produced through the bremsstrahlung
technique: electron beam from accelerator impinges
on a radiator, scattered electrons produce
bremsstrahlung with the typical spectral distribution
1/Eγ, with energy up to 3.2 GeV. The purpose of the
experiment is to study a wide class of reactions
induced by photons on nucleons and nuclei with
production of pseudoscalar mesons (π0,η),
pseudovettorial mesons (ω, ρ, θ) and the precise
determination of the properties of baryonic resonances,
in the energy region from threshold to 3.5 GeV using a
polarized gamma-ray beam and/or polarized targets.
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The activities will be held in Bonn in the B1project[10]
at the Physikalischen Institute of the Rheinischen
Friedrich Wilhems-Universität. The involved groups
and organisations are coming from Russia, Ukraine,
Italy and Germany. First data taking is scheduled for
the biginning of the next year.
BGO-OD experimental set-up
A schematic view of the experimental apparatus
installed in the beamline S-Bonn[11] is shown in fig.
4. The experimental setup is a combination of an open-
dipole forward spectrometer optimized for the
detection of charged particles and of a large solid angle
(25-155 degrees) detector, the BGO crystal ball, that
covers the central angular region and is optimized to
detect neutral particles. This particular set-up
configuration is well designed to allow the
investigation of photoproduction reactions and
discrimination of multi-particle final states with
different charges. Dipole field together with multiple
tracking sections allows for momentum/charge analysis
of reaction products not possible in previously
experiments.
The polar angular region of small angles, θ<12°, is
covered by B1 magnetic spectrometer that produces a
dipolar field of about 0.5 T and that will be used for the
separation, identification and reconstruction of the
momentum (resolution 0.5%) of charged particles
emitted in the photoproduction process . For this
purpose, the spectrometer is equipped with:
a first track scintillating fibers detector (MOMO
detector in fig.4) made of 672 fibers arranged on 3
layers, which allow to have a spatial resolution of 1,5
mm;
an aerogel Cĕrenkov detector for the discrimination
of charged pions from protons and particulary from
charged kaons in the 600-1500 MeV/c range;
a second track scintillating fibers detector (SciFi2)
that consists of 640 scintillating fibers arranged in 4
circular layers;
two set of double plane drift chambers for particle
tracking, placed at the exit of the dipole;
a time-of-flight detector (TOF) which provides time
flight measurements for charged particles and neutrons.
The central region is covered by:
the BGO, (Bi4Ge3O12), an homogeneous
electromagnetic calorimeter made of 480 truncated
pyramidal crystals placed inside 24 carbon fiber
baskets each one containing 20 crystals and supported
by an external steel structure. Each crystal is 24 cm
long (21 radiation lenghts) and provides an high energy
resolution for photon detection ( ≈ 3% FWMH at
1GeV) a good response for proton with energy up to
400 MeV and a good neutron detection efficiency. The
angular resolution is of about 6-8 degrees. The
characteristics of the response time of the calorimeter
allow to use the signal for the experimental trigger.
Each crystal is coupled to one phototube for the read
out of the signals. The detector is property of INFN
and used in the GRAAL experiment closed at the end
of 2008;
a crystal barrel detector, made of 32 plastic
scintillator bars, which allows, through
measurement of ΔE, the discrimination between
charged and neutral particles and,
in combination with the information of energy released
in the calorimeter, the identification of charged
particles (protons and pions);
multi wire proportional chambers (MWPC's) for
inner tracking;
multi resistive proportional chambers (MRPC's) for
forward tracking;
target of H2 or deuterium that is tight enclosed by
the BGO.
Fig.4 Overview of BGO-OD experimental set-
up at the beam line S
Physical program
The principle aim of this experiment is the
systematic investigation of the photoproduction of
mesons off the nucleon. These processes are related to
the structure of both, the mesons and baryons
involved, whose nature of strong bonds must still be
considered as poorly understood. Only such improved
experiments will shed new light on the low-energy
hadronic aspects of the strong interaction. Polarisation
measurements are indispensable to characterize the
relevant degrees of freedom in the production process
of the different mesons, in particular the formation and
role of the missing resonances. Therefore, meson
photoproduction provides an ideal tool to investigate
particular baryonic states which challenge the quark
model through their unusual features. The
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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photoproduction of mesons off the nucleon provides
also access to several aspects of low-energy strong
interaction. The mechanisms involved are not clear, in
many cases not even the relevant degrees of freedom,
from which resonance spectra depend. Of particular
interest are the excitation and subsequent decay of
baryon resonances, as well as intermediate particle
exchanges in the production process, especially
important in vector-meson production. To achieve one
of the central goals of low-energy hadron physics, to
disentangle and understand the complicated nucleon
resonance spectrum, a better understanding of the
meson production mechanisms is an indispensable
prerequisite. It is also the basis to understand the
features and hence the structure of individual states
which in a striking manner do not fit to the description
of quark models. Open problems are: (i) the
mechanism and the relevant degrees of freedom in the
photoproduction of mesons, (ii) the contrast between
the general spectroscopic success of quark models and
the vast discrepancy between expected and observed
number of states, (iii) the structure of some well
established resonances which is still not well
understood.
In order to try to solve these problems, processes
beyond single pion photoproduction must be
investigated. Final states that involve multiple pions, η,
η', K, K*, ω and θ mesons, or combinations thereof (it
should be stressed that some of this mesons have
masses bigger than photon beam maximum energy). It
is clear that progress in this field means approaching to
an understanding of the complex nature of the deepest
bonds of matter known so far.
Experimentally, the new B1 magnetic spectrometer
will provide high resolution and good particle
identification for charged final states, in particular for
K±. Since the acceptance of the spectrometer extends to
almost 0-degree forward direction, it is ideally suited to
investigate θ production through simultaneous K+ and
K- detection. Moreover, the high resolution detection of
recoil protons may not only add to our understanding
of the basic production process, but also favour
precision measurements regarding the in-medium
properties of the ω meson. Finally, combination of the
crystal calorimeter and the forward spectrometer yields
a unique instrument for complicated multi-particle final
states and in this way gives us access to the study of a
wide range of phenomena in particle physic.
BGO CALIBRATION-EQUALIZATION
In this paragraph we report an overview on the
calibration-equalization operations performed on the
BGO calorimeter crystals.
We performed not a simple calibration of BGO
crystals but, more important, we also made an
equalization of crystals varying high voltage applied to
phototubes to homogenize their response.
The operations can be performed by remote and still
continuing now in Messina.
Fig.5 Scheme of the experimental calibration
chain
In fig.5 we can see a roughly representation of the
experimental chain of calibration: the output signal
from the phototube, coupled to the crystal, is sent to a
mixer reducing its amplitude and then reaches the
ADC module for the readout. We worked on the
calibration of 64 crystals at time of the 480 crystals
(four ADC available for acquisition with 16 channel
each one, in future with a full equipped BGO
elettronics, we will have 30 ADC to acquire
simultaneously signal from the 480 crystals). For the
calibration we used three sources of 22Na, located
inside the BGO cylindrical hole, which is characterized
by two emission peaks: the first at 0.511 MeV and the
second at 1.275 MeV. In order to derive the calibration
constants for each channel, we tried to fix the energy of
the second peak at the channel 480 of the ADCs, we
also made an equalization of the crystals by changing
the high voltage applied to the fototubes in order to
obtain the response, (calibration peak), at the same
channel of ADC for all crystals.
The calibration constant is about 0.021 MeV/
channel. The peaks have also been monitored in time
and the fluctuations of the position of the second peak,
due to the fitting procedure and to the response of
crystal+ADC to the source, is of about 1-2 channels
corresponding to about 0.021-0.042 MeV. This means
an incertitude of about 1,6%-3,2% of the energy. The
intrinsic resolution of the BGO+ADC at 1.275 MeV is
about 25%-30%.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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Fig.6 Example of signal acquisition
BIBLIOGRAPHY
[1] A. Fantini et al. Phys. Rev. C 78, 015203(2008); [2] R. Di Salvo et al. Eur. Phys. J A 42,151 (2009);
[3] G. Mandaglio et al. Phys. Rev. C 82, 045209 (2010);
[4] M. Gell-Mann, Phys. Lett. 8 (1964) 214; [5] O.W. Greenberg, Phys. Rev. Mt. 13 (1964) 598;
[6] R.H. Dalitz, Proceedings of the XII Int. Conf. On High Energy
Physics Berkeley, Calif. (1966); [7] M. Anselmino et al., Rev. Mod. Phys. 65 (1993) 1199;
[8] R. Bijker, F. Iachello, A. Leviatan, Ann. Phys. 236 (1994) 69;
[9] R. Bijker, F. Iachello, and A. Leviatan, Phys. Rev. D 55 (1997) 28;
[10] http://b1.physik.uni-bonn.de/;
[11] http://b1.physik.uni-bonn.de/ExperimentalSetup.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
71
RESONANT LASER ABSORPTION AND SELF-FOCUSING EFFECTS
PRODUCING PROTON DRIVEN ACCELERATION FROM
HYDROGENATED STRUCTURES
M. Cutroneo1,2
and L. Torrisi1
1Dottorato di Ricerca in Fisica, Università di Messina, V.le F. Stagno D’Alcontres 31, 98166 S. Agata (ME), Italy
2Centro Siciliano di Fisica Nucleare e Strutt. della Materia, V.le A. Doria 6, 95125 Catania , Italy
* Corresponding author, e-mail: mari.cutroneo@unime.it
Abstract
Resonant laser absorption and self-focusing effects
were investigated as two typical non-linear processes
occurring inside laser generated non-equilibrium
plasmas.
The ion emission in laser-generated plasma is dealt
at low and high intensities from 1010
W/cm2 up to
values higher than 1016
W/cm2. The properties of
plasma are strongly dependent on the time and space,
laser parameters (intensity, wavelength, pulse duration,
spot dimension, focal position…), target composition
(polymers, metals, ceramics) and target geometry
(thickness, spot/thickness ratio, surface curvature,…).
A considerable interest concerns the energetic and
intense proton generation for the multiplicity use that
proton beams have in different scientific fields
(Nuclear Physics, Astrophysics, Bio-Medicine,
Microelectronics, Chemistry,…).
Measurements have been performed at INFN-LNS in
Catania and at PALS Laboratory in Prague, by using
low and high laser pulse intensities, respectively. Thick
and thin targets and different detection techniques of
ion analysis have been employed.
The mechanisms of resonant absorption of the laser
light, produced in specific targets containing
nanostructures with dimensions comparable with the
wavelength and high electron density, enhances the
proton yield and the proton kinetic energy as result of
resonant absorption effects.
The mechanisms of self-focusing, obtained by
changing the laser focal distance from the target
surface, increase the local intensity due to further
focalization the laser light in the dense vapour and
consequently the plasma temperature, the density and
Coulomb ion acceleration. Real-time ion detections
were carried out through Thomson parabola
spectrometer (TPS) coupled to a multi-channel-plate
(MCP). Ion collectors (IC), SiC detectors and ion
energy analyzer (IEA) have been also employed in
time-of-flight configuration (TOF) technique.
The energy and the amount of protons and ions
increase significantly when the two investigated non-
linear phenomena occur, as it will be discussed.
Introduction
The interaction of short laser pulses with solids has
become an important field of study because of many
applications, such as the fast ignition scheme of inertia
confinement fusion, the plasma-based particle
accelerator, coherent x/ -ray sources, etc.. For most of
these applications, the nature of the absorption process
must be determined.
The density scale length of the plasmas generated
from the target surfaces can be estimated as:
s pL c (1)
where cs is the ion sound speed and p is the laser
pulse duration [1]. For high intensities (> 1016
W/cm2)
and very short pulses (< 1 ps)) the scale length is too
short to generate sufficient absorption effects and
resonance absorption at the critical surface is suggested
to be one of the major absorption mechanisms. Some
experiments show that it plays an important role even
for plasmas with a scale length considerably shorter
than the laser wavelength 0. However many
theoretical works on resonance absorption are valid for
the case in which L > 0 [2]. At higher laser intensity
the electrons being pulled out by the ponderomotive
forces and then returned to the plasma at the interface
layer by the wave field can lead to a phenomenon like
wave breaking. Thus, the electron plasma wave is hard
to develop and vacuum heating tends to be dominant
[3].
A simple model is used to calculate the energy
absorption efficiency when a laser of short pulse length
impinges on a dielectric slab that is doped with an
impurity with a resonant line at the laser frequency. It
is found that the energy absorption efficiency is
maximized for a certain degree of doping concentration
(at a given pulse length) and also for a certain pulse
length (at a given doping concentration). Absorption
processes are generally dependent on the density scale
length.
Interaction of the laser radiation above some
threshold intensities with a plasma of defined
properties may significantly increase the charge state
and energy of the produced ions, due to a peculiar
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
72
effect occurring in the plasma, which focalizes further
the laser pulse (self-focusing effect) acting so as a
small vapor lens placed in front of the target surface.
Advances in laser technology have recently enabled the
observation of self-focusing in the interaction of
intense laser pulses with plasmas. Self-focusing in
plasma can occur through thermal, relativistic, and
ponderomotive effects [4]. Thermal self-focusing is
due to collisional heating of plasma exposed to
electromagnetic radiation: the rise in temperature
induces a hydrodynamic expansion, which leads to an
increase of the refraction index and further heating.
Relativistic self-focusing is caused by the mass
increase of electrons traveling at speed approaching the
speed of light, which modifies the plasma refractive
index, depending on the electromagnetic and plasma
frequencies. Ponderomotive self-focusing is caused by
the forces which push electrons away from the region
where the laser beam is more intense.
Both non-linear effects of resonant absorption and
self-focusing were investigated in order to produce
high yield of energetic proton emission from laser
irradiated targets, as will be presented and discussed.
Experimental set-up
The main experiments have been performed by using
the Nd:Yag laser of INFN-LNS in Catania and the
Iodine Asterix laser of PALS Laboratory in Prague.
The first has been employed at 1064 nm, 9 ns pulse
duration, 800 mJ maximum pulse energy, with
intensities between 108 and 10
11 W/cm
2. The second
has been employed at 1315 nm (1 ), 300 ps pulse
duration, 600 J maximum pulse energy, with intensities
between 1013
and 1016
W/cm2.
In order to generate protons, the irradiated targets
were thick and thin hydrogenated solids. Many of these
were polyethylene based (CH2-monomer) with
additions of nanostructures such as carbon-nanotubes
(CNT), of length of the order of 1 micron, and oxides
(such as Fe2O3). Other targets consisted of
hydrogenated Si, thin films of mylar covered by Au or
Al films, hydrates and metals. Generally thick films (1
mm thickness) were used at LNS for irradiation at low
laser intensities to generate backward directed plasmas,
while thin films (of the order of 1 micron in thickness)
were employed at high laser intensity at PALS in order
to generate forward directed plasmas.
Time-of-flight (TOF) measurements have been
obtained with ion collectors (IC), semiconductor
detectors based on SiC, and electrostatic deflector ion
energy analyzer (IEA) that permits to measure the
average ion energy, the ion energy and the charge state
distributions, respectively. Details on IC, SiC and IEA
detector are given in literature [5,6].
The ion plasma temperature, Ti, was measured
though the Coulomb-Boltzmann shifted (CBS) fit of
the experimental ion energy distributions given by the
IEA spectrometry [7]; the electronic plasma
temperature, ne, was measured through the evaluation
of the ablation yield (atoms removed from the laser
crater per laser shot) and the volume of the visible
plasma observed by a fast CCD camera.
A Thomson parabola spectrometer (TPS) couplet to
a multi-channel plate (MCP) was also employed at
PALS in forward direction along the normal to the
target surface in order to separate the different ions
contributions by means of magnetic deflection by using
a magnetic field of the order of 0.1 Tesla and an
electric deflection of 3 keV/cm. A scheme of the TPS
is reported in Fig. 3b. TPS measures the energy, charge
states and ion species of ejected particles from plasma
for comparison with simulation programs.
Finally, a streak camera was employed at PALS to
measure the laser focal position (FP) distance with
respect to the target surface. Negative distances mean a
focus in front of the surface while positive distances
mean a focus inside the target.
Fig 1. Typical IC spectra obtained at low intensity
relative to pure polyethylene irradiation (a) and
typical resonant absorption obtained by irradiating
CNT nanotubes, 0.1% in concentration, embedded in
polyethylene (b).
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
73
Results
At low intensities, of the order of 1010
W/cm2 a
typical spectrum of ions emitted from polyethylene and
detected by IC shows a large and slowly peak due to
the carbon charge states and a faster peak due to
protons, as reported in Fig. 1a.
Fig. 2: Typical proton energy distribution
relative to the ion emission from low intensity
laser irradiation of pure polyethylene (a) and
relative to that from Silicon hydrogenated
nanospheres target irradiated in the same
experimental conditions (b).
In this case the TOF distance is 60 cm, thus the
corresponding proton peak energy is about 75 eV. Pure
polyethylene shows a low absorption coefficient to
1064 nm and a low electron density. Embedding CNT
nanostructures in polyethylene the absorption
coefficient changes strongly thus the result of the ion
emission at low laser intensity, also, as reported in Fig.
1b. The SEM photo of the carbon nanotubes is reported
in the inset of the figure. In this case the TOF length
was 150 cm thus the corresponding maximum proton
energy, calculated at the FWHM of the proton peak, is
about 120 eV. The comparison between the two spectra
shows that the proton/carbon ratio increases from 0.05
in pure polyethylene up to 1.5 for 0.1% concentration
of CNT. Thus the insertion of absorbent
nanostructures, with length comparable with the laser
wavelength, produces effects of resonant absorption
that can be responsible of the strong increment of the
proton yield emission while a negligible proton kinetic
energy increment is recorded. However, significant
increment of the proton energy can be obtained using
other special nanostructures inducing resonant
absorption effects.
At low laser intensity, a typical energy distribution
of the protons emitted from an irradiated polyethylene
target is reported in Fig. 2a. It gives average proton
energy of about 100 eV. For comparison, the proton
energy distribution obtained by irradiating amorphous
surface layers of hydrogenated silicon (Si:H) with 100
nm diameter nanospheres is reported in Fig. 2b. The
SEM photo of the nanospheres is reported in the inset
of the figure. It gives maximum proton energy above
1.5 keV. This result may be due to a strong resonant
effect generated by the high electron density of the first
layers of the high absorbent target.
At high intensity, of the order of 1016
W/cm2, the
produced plasma show high electron densities and the
resonant absorption effects becomes more probable. A
typical spectrum of ions emitted from CNT nanotubes
embedded in PMMA target is provided by the
Thomson Parabola spectrometer placed in forward
direction along the normal to the target surface.
The comparison of the experimental parabolas (Fig.
3a) with the simulation spectra (Fig. 3c) allows us to
evaluate the particle masses, energy and charge states.
The spectra indicates a maximum proton energy of
1.5 MeV namely, higher value than those determined
by using polyethylene targets without nanotube
inserted.
The complexity of the laser interaction mechanisms
with solid targets is due to the non-linearity of the
processes occurring in the pre-plasma and of the
plasma non linear optical properties which are
dependent on the laser intensity and that occurs
generally above a threshold of about 1014
W/cm2 [8].
Self-focusing effects, for example, increases the
intensity of the part of laser beam on the target due to
the higher focusing which may reduce the spot up to
dimensions comparable with the laser wavelength.
Evidence of the self-focusing occurrence may be given
by IEA spectrometer of the emitted particles indicating
ion energy, masses and charge states.
The plot of the ion yield versus the focal position
indicates that for low charge states ions are due to
ionization by thermal electrons generated by inverse
bremsstrahlung mechanism. In contrast, ions with
higher charge states, connected with the presence of
fast electrons, and generated by resonant absorption
mechanisms, create a maximum yield, kinetic energy
Yie
ld
(V)
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
74
and charge sates when the laser focal position if placed
near and in front of the target surface.
Fig. 3: Typical experimental spectrum related to
Thomson Parabola placed in forward direction
with respect to the thin target with nanostructures
embedded in polyethylene (a), scheme of the TPS
spectrometer (b) and comparison with the
parabola simulation plot (c).
In the dense vapor generated in front of the target, in
facts, the ambipolar acceleration of ions due to non
linear forces, including ponderometive relativistic and
self-focusing, which lead to very high laser intensity in
a self-focused channel may become the main reason for
the presence of high kinetic energy and high charged
ions. Such a result was ascribed to the volume effect of
produced plasma due to the interaction of continuously
decreasing diameter of the laser beam with respect to
the target surface that, in the case of self-focusing
mechanisms, is found to a forward negative focus
position.
Fig. 4a shows a typical example of IEA spectrum
obtained by irradiating Au target in no condition of
self-focusing, when the focal position is FP = + 500
m, with the focal position inside the target and high
spot dimension.
In such conditions the self-focusing cannot happen
because the intensity is below the threshold value and
the number of charge states is only six. The inset of the
figure shows a streak camera X-ray image and a
scheme indicating with high precision the used focal
position. Fig. 4b shows a typical example of IEA
spectrum in conditions of self-focusing, when the focal
position is FP = -200 m.
In such conditions the number of charge states is
about 56 as result of hotter energetic plasma. Also in
this case the inset of the figure shows the streak camera
X-ray image and the scheme indicating the used focal
position. This last effect occurs because the high light
refraction effect produces a further laser beam
focalization, due to the dense plasma volume in front
of the target, which converges the beam so as a
focusing lens.
At higher intensities the data were collected from
literature and compared with our measurements in
order to evaluate the generalized law of I2 scale factor
[9].
Generally a linearity of processes occurs with the
law I2, however over linear dependences occur when
resonant absorption and self-focusing take place.
Discussion and conclusions
The existence of an optimum laser focus position for
generation of the fastest ions with the highest charge
states in front of the target surface is consistent with
literature [10]. The course of dependencies and similar
values of the highest Zmax indicate a threshold for the
appearance of relativistic self-focusing of laser beam
and a principal limitation of the maximum attainable
laser intensity. At PALS differences for 1 and 3
could be ascribed to a different absorption of laser
radiation, in accordance with the scaling relation I2.
The front part of the 300 ps laser pulse interacts with
the target and creates an expanding plasma plume.
Considering for simplicity, the expansion velocity v =
Detector
s
z
x
-V/2
+V/2
B E
N
S
gegmD1
L12
D2
L1
Ld1
Ld2L2
Pinholes
Detector
s
z
x
-V/2
+V/2
B E
N
S
gegmD1
L12
D2
L1
Ld1
Ld2L2
Pinholes
C5+
a) Thomson Parabola
Spectrometer
C2+
C3+
C4+
H+
Ep = 1.5 MeV
b)
c)
C 5+
a)
Thomson Parabola
Spectrometer C 2+
C 3+
C 4+
H+
c)
C 1 +
C6+
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
75
106 m/s, the plasma plume attains the distance of 100
m within the first 100 ps. For the laser beam diameter
of 70 m, the self-focusing length should be about 100
to 200 m, at least. For FP = 0, the more the plasma
plume expands, the longer the interaction length, but
the lower the laser intensity with which the front of the
plasma interacts.
Fig. 4 Typical IEA spectrum obtained at high
intensity laser at PALS laboratory in Prague
relative to Au target irradiated in no self-
focusing condition (a) and in self- focusing
condition (b).
The following conclusions can be made:
Nano and micrometric structures, such as carbon
nanotubes, polymeric chains and molecular groups
with dimensions comparable with the laser wavelength
may induce resonant absorption effects increasing the
plasma temperature and the acceleration ion drive
mechanisms;
Resonant effects seem to be influenced by structure
and composition of the target, by the plasma frequency
and occur at high intensity and in the contrary of the
literature also at low intensities, like we showed in this
work.
Self-focusing processes influence significantly the
generation of ions with the highest charge states, using
high power iodine laser with the pulse length of 300 ps
and an optimal FP distance can be found to enhance
this effect of intensity increase due to the focal spot
decreasing.
Acknowledgements
Work supported by LaserLabEurope (Project No.: pals
001653) and by INFN-LIANA Project.
References [1] H. Cai, W. Yu, S. Zhu, C. Zheng, L. Cao, B. Li, Z. Y. Chen and
A. Bogerts, Physics of Plasmas 13, 094504, 2006; [2] W. L. Kruer, Physics of Laser Plasma Interactions Addison-
Wesley, New York, 1988;
[3] S. C. Wilks and W. L. Kruer, IEEE J. Quantum Electron. 33, 1954, 1997;
[4] L. Torrisi, D. Margarone, L. Laska, J. Krasa, A. Velyhan, M.
Pfeifer, J. Ullschmied, L. Ryc Laser and Particle Beams 26, 379-387, 2008;
[5] E. Woryna, P. Parys, J. Wolowski, and W. Mroz, Laser Part.
Beams 14, 293, 1996; [6] L. Torrisi, G. Foti, L. Giuffrida, D. Puglisi, J. Wolowski, J.
Badziak, P. Parys, M. Rosinski, D. Margarone, J. Krasa, A.
Velyhan and J. Ullschmied J. Appl. Phys. 105, 123304, 2009; [7] L. Torrisi, S. Gammino,L. Andó, L. Laska, J. Krasa, K.
Rohlena, and J. Ullschmied, J. Wolowski, J. Badziak, and P.
Parys J. of Appl. Physics 99, 083301, 2006; [8] L. Laska, L. Ryc, J. Badziak, F.P. Boody, S. Gammino, K.
Jungwirth, J. Krasa, E. Krousky, A. Mezzasalma, P. Parys, M.
Pfeifer, K. Rohlena, L. Torrisi, J. Ullschmied and J. Wolowski Rad. Eff. & Def. in Solids 160 (10–12) (2005) 557–566;
[9] L. Laska, K. Jungwirth, J. Krasa, E. Krousky, M. Pfeifer, K.
Rohlena, J. Ullschmied, J. Badziak, P. Parys, J. Wolowski, S.
Gammino, L. Torrisi and F.P. Boody, Laser and Particle Beams
24(1), 175-179, 2006;
[10] L. Laska, K. Jungwirth, J. Krasa, M. Pfeifer, K. Rohlena, J. Ullschmied, J. Badziak, P. Parys, L. Ryc, J. Wolowski, S.
Gammino, L. Torrisi and F.P. Boody, Czech. J. of Physics 55
(6), 691-699, 2005.
NO SELF- FOCUSING
SELF- FOCUSING EFFECT
TOF ( s)
a)
b)
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
77
BARYON SPECTROSCOPY BY VECTOR MESON PHOTO-PRODUCTION
AT BGO-OD EXPERIMENT
V. De Leo a,b,*
, F. Curciarello a,b
, G.Mandaglio a,b
, M.Romanyuk a,b,c
, G.Giardina a,b
.
a)Dipartimento di Fisica, Università di Messina, I-98166, Messina, Italy
b)INFN- Sezione Catania, I-95123,Catania, Italy
c)Institute for Nuclear Research, National Academy of Science of Ukraine, Kiev, 03680, Ukraine
* Corresponding author, e-mail: vdeleo@unime.it
Abstract
The study of baryon resonances plays the same role
for understanding of the nucleon structure as the
nuclear spectroscopy was for the investigation on the
atomic nucleus structure. Excitation energies and
quantum numbers of the low lying nucleon resonances
are well known. Properties like mass, spin, and parity
alone , however, do not offer stringent tests of hadron
models. Much more crucial tests are provided by the
investigation of transitions between the states, which
reflect their internal structure. The dominant decay
channel of nucleon resonances is the hadronic decay
via meson emission. Photo-production of mesons,
which carries information on strong and
electromagnetic decay properties, therefore provides a
very valuable tool for their study. The progress made in
the last years in accelerator and detector technologies
has largely enhanced our possibilities to investigate the
nucleon with different probe. The new generation of
electron accelerators equipped with tagged photon
facilities have opened the way to meson photo-
production experiments of unprecedented sensitivity
and precision. The possibilities of the starting
international experiment BGO-OpenDipole (linked to
the I.N.F.N. MAMBO experiment) at the ELSA
facility of Bonn, which involves the hardware testing-
improvement and software production contributions of
the Messina group will be described in detail in the
present report. The experiment represents a new
sophisticate electromagnetic probe for the investigation
of baryon resonances by the meson decay detections.
Introduction
Current issues in the understanding of the strong
interaction address the structure of hadrons, consisting
of quarks and gluons, as the building blocks of matter.
Central challenges concern the questions why quarks
are confined within hadrons and how hadrons are
constructed from their constituents. One goal is to find
the connection between the parton degrees of freedom
and the low energy structure of hadrons leading to the
study of the hadron excitation spectrum but the
excitation spectrum of the system does not provide
very sensitive tests of models [1]. The crucial tests
come from the investigation of transitions between the
states which are more sensitive to the model wave-
function. The dominant decay channel of nucleon
resonances is the hadronic decay via meson emission
to the nucleon ground state [2]. However, photon decay
amplitudes are also of great interest since the photon
couples only the spin flavor degrees of freedom of
quarks and therefore reveals their spin-flavor
correlation which are related to the configuration
mixing predicted by the QCD [3]. Perturbative QCD at
high energies deals with the interactions of the quarks
and gluons. However, our picture of the nucleon has
much more to do with effective constituent quarks and
mesons that somehow subsume the complicated low
energy aspects of the interaction which generate the
nucleon many body structure of valence quarks, sea
quarks and gluons. The most important step towards an
understanding of nucleon structure is therefore the
identification of the relevant low-energy effective
degrees of freedom. Most nucleon models are based on
three equivalent constituent quarks interacting via
some QCD ―inspired‖ interaction. However, models
based on quark-diquark (q – q2) configurations were
also suggested and more molecular-like pentaquark
( qqq qq ) structures have been discussed in the
context with certain ―nucleon‖ resonances. From the
experimental point of view the main difference
between nuclear and nucleon structure studies results
from the large, overlapping widths of the nucleon
resonances and much more important non resonant
background contributions which both complicate
detailed investigations of the individual resonances.
The existing data for nucleon resonances were
mostly determined by πN scattering. The comparison
of the set of resonances predicted by modern quark
models with the set of experimentally established
resonances resulted in the so-called ‘missing
resonances‘ problem [4]: more resonances are
predicted than observed. This problem encouraged the
use of the photo-production of mesons as an alternative
tool to excite the resonances. The advent of a new
generation of electron accelerators allowed to perform
meson photo-production experiments of unprecedented
sensitivity and precision [5].
Pion scattering on a proton target has been chosen as
the best tool to excite and to study the resonances of
the nucleon. Nucleonic resonances are excited states of
the nucleon with large mass width but with well
defined spin, isospin and parity. Their identification
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
78
and their characterization were carried out through the
analysis of the pion-nucleon scattering data by partial-
wave phase-shifts method. In this method, the
excitation of a given resonance is searched with the
amplitude behaviour of a specific partial wave in a
characteristic plot called Argand diagram [6].
The Jπ
of the pseudo-scalar mesons (pions, eta,
kaons) is 0−. The J
π of the vector mesons (rho, omega)
is 1−. The isospin of pions, kaons and η is 1, 1/2 and 0
respectively. The isospin is 1 for ρ and 0 for ω. All of
the mesons have a short lifetime (≤ 10−7
s); however, π±
and K± may have a path of several meters in the
laboratory and then be detected with standard detectors
similarly to stable charged particles, whereas η, η' , ρ
and ω decay almost at their production point. It is
worth mentioning that the rare decay modes are used as
special tools to test chiral perturbation theory and basic
invariance principles.
Experimental set-up.
A schematic view of the experimental apparatus used
in the S-beamline of Bonn is shown in Figure 1. The
Electron Stretcher Accelerator consists of three stages
(injector LINAC, booster synchrotron and the stretcher
ring) and provides a beam of polarized and unpolarized
electrons with a tunable energy of up to 3.5 energy
GeV. The bunched electron beam impinges on a
radiator. Scattered electrons produce bremmstrhalungg
with the tipical 1/Eγ spsectral distribution.
The polar angular region of small angles (θ < 12°) is
covered by B1-magnetic field spectrometer that
produces a dipolar field of about 0.5 T and that will be
used for the separation, identification and
reconstruction pulse resolution (0.5%) of charged
particles emitted in the photo-production process.
Figure 1. Schematic view of S - beamline
accelerator ELSA in Bonn.
For this purpose, the spectrometer is equipped with:
- MOMO is a scintillating fiber vertex detector with
672 channels. It consists of three layers of 224 parallel
fibers (2.5mm diameter) each. The layers are rotated by
60° against each other. The arrangement yields a
circularly shaped sensitive detector area of 44cm
diameter. The spatial resolution is about 1.5mm,
yielding effectively more than 50 000pixels. A 5cm
wide central hole allows the photon beam to pass
through [7].
Figure 2. MOMO detector.
- The aerogel Čerenkov detector (ACD) that serves
to reliably discriminate pions against protons, and
particularly improves the K± identification
substantially.
- SciFi2 detector where an active area of 66cm x
51cm is obtained using 640 scintillating fibers with a
diameter of 3mm [7].
Figure 3. SciFi2 detector.
A central hole (4cm x 4cm) allows the beam to pass
through. Groups of 16 fibers are glued together to form
a so-called module. The design guarantees a minimum
path length (about 2mm) for particles traversing the
circular fibers. The modules are arranged in two layers
twisted by 90 degrees.
- Tracking of charged particles behind the
spectrometer magnet is performed with eight horizontal
drift chambers (DCs) which are built at the PNPI
Gatchina. To cover the necessary angular range each
DC has a sensitive area of at least 2456mm × 1232mm.
The photon beam has to penetrate the DCs. The
distance of the chambers from the target will range
from 3.7 m for the first chamber up to 4.7 m for the
last. For accurate positioning and simplified handling
the chambers will be hanging from two support beams
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
79
attached to the magnet. Four of the chambers will be
rotated by ± 9 degree around the beam axis. With two
of the remaining chambers having horizontal wires and
the other ones vertical wires four different wire
orientations are obtained.
- The forward spectrometer will be complemented by
a time-of-flight (TOF) detector, which is an essential
component for particle identification, because it
provides flight-time measurements for both, charged
particles and neutrons. It has to cover the inner 10-12
degree angular range at a distance of 5m downstream
of the target. It consists of four walls with a 3×3 m2
front surface, mounted on independent mechanical
stands. Each wall houses 14 individual scintillating
bars of 3000 mm × 200 mm × 50 mm size with
photomultiplier readout at both ends.
The polar angular region between 25 and 155
degrees is covered by:
- The BGO (Bi4 Ge3 O12) Rugby Ball is a large
acceptance calorimeter designed to measure multi-
photon states with excellent energy resolution. The
design of the calorimeter has taken into consideration a
constant thickness in every direction and a central hole
of radius 100 mm for the passage of the beam, target
and inner detector housing. The resulting structure is
made of 480 truncated pyramidal crystals of 240 mm
length (corresponding to ~ 21 radiation lengths)
arranged in a 15×32 matrix covering the polar angles
from 25° to 155° and the whole azimuth for a total
solid angle ΔΩ = 11.3 sr. The mechanical structure
consists of 24 carbon fibers baskets, each containing 20
crystals, and supported by an external steel frame.
Figure 4. Overhead view of the BGO
calorimeter.
The baskets are divided into cells to keep the crystals
mechanically and optically separated. The thickness of
the carbon is 0.38mm for the inner walls and 0.54 mm
for outer walls. The steel support frame is separable
into two moving halves to allow to access the central
part of the detector [7].
- A cylinder of 32 plastic scintillator bars, which
allows, trough the ΔE measure, the discrimination
between charged and neutral particles and in
combination with the energy released in the
calorimeter, the identification of charged particles
(protons and pions).
- The target can be a proton or deuterium target.
Hardware testing
To install the BGO system in Bonn it was necessary
to replace most of electronic acquisition and HV
distribution system to the crystal.
The reading of the BGO signal amplitude is made by
sampling ADC modules 32 -channel multiplexer. The
main characteristics of the ADC modules (AVM16
MAMBO) are the following:
-Sampling frequency 160 MHz (= 6.25ns)
-12 bit resolution (corresponding to 4096 channels)
-16 signal input and one trigger input.
The sampling of the signal occurs within a time
interval defined by the user that can begin even before
the trigger signal (in our case the time window width is
800ns). The initial samples (four) are dedicated to the
determination of the baseline event subtracting
automatically the value determined at the signal; the
outgoing signal is thus cleaned of any background. The
tests on the ADC modules were performed working
with external signals and triggers, coming from a pulse
generator by setting 9 different possible offset values
on the baseline value. For each baseline, we have been
sending a pulser signal with an amplitude varying from
100 mV to 10 mV with steps of 10 mV. The signal
coming from the pulser is a wave with trapezoidal
shape, time width 200 ns, rise time 5 ns, frequency 1
kHz. The procedure followed for the tests with the
pulser and different baselines is the following: at first
no signal is sent to the ADC and the baseline offset is
set; then the baseline register is read and only at this
time the signal is sent to the ADC. The value of 100
mV on the pulser current is fixed and then the baseline
register is read again and the acquisition program is
started; thus the acquisition program is stopped and the
value of 90 mV on the pulser current is fixed. As
before, the baseline register is read again and the
acquisition program is started; this procedure is made
for ten values of current (form 100 mV to 10 mV). The
test results have highlighted some problems of the
ADC modules. Strong difference was shown in the
extracted value of the total integral (Qtot) with a same
input signal between different modules and different
channels. The response of the ADC channels to a fixed
input strongly depends on the baseline offset (the
response strongly increases with baseline value
reaching a ―plateau‖ only for the higher baseline
values). The linear behavior was checked and it was
confirmed for almost all baseline offset values but the
strongly dependence of the gain on the baseline offsets
affects the ADC linearity. Therefore, the time
synchronization features between ADC modules have
been verified. The tests on ADC modules have enabled
their improvement.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
80
Physics
The goal of this project is the systematic
investigation of the photoproduction of mesons off the
nucleon. Polarization measurements are indispensable
to characterize the relevant degrees of freedom in the
production process of the different mesons, in
particular the formation and role of hadronic
resonances. The photoproduction of mesons off the
nucleon provides access to several aspects of low-
energy strong interaction.
The quark model predicts a large number of nucleon
resonances which have not yet been observed [8].
Since the most used reaction for their study was pion-
nucleon scattering, one could infer that these so-called
‗‗missing resonances‘‘ may couple weakly to this
channel[9]. One possibility to investigate this issue is
the photo-production of ω mesons off the proton. This
channel is interesting for several reasons: first, there is
no nucleon resonance well-established decaying by ω
emission; second, the threshold of ω-photoproduction
lies in the third resonance region, which is less
explored than the first two; third, from the sparse data
in the literature and a new generation experiment,
evidence for resonance excitations in
γ p→ ωp is still not obvious.
Due to the fact that the ω is isoscalar (I=0), the s-
channel production of this meson is only associated
with the decay of N∗ (I=1/2) states and not the decay of
Δ∗ (I=3/2) states, which greatly simplifies the
contributing excitation spectrum. However the vector
meson character of the ω implies that at least 23
observables have to be measured to disentangle all
contributing resonances, instead of 8 in the
pseudoscalar case. It can be hoped however, that fewer
than 23 observables already provide significant
constraints. In any case, the measurement of
polarization observables will provide important
information about the ―production mechanism‖ of the
ω meson[10]. At high photon energies resonances play
no role.
The cross section of vector-meson production off
nucleons falls off exponentially with the squared recoil
momentum, t, corresponding to the range of the mutual
interaction. The t dependence of the cross section,
which is approximately the same for all sufficiently
high photon energies, is characteristic for
‗‗diffractive‘‘ production. It is associated with the
exchange of natural parity quantum numbers (Fig. 1
left) related to the Pomeron, a composite gluonic or
hadronic structure.
At large |t| deviations from pure diffraction show up.
From the comparison to QCD-inspired models which
are also able to describe φ and ρ0 photoproduction, the
presence of hard processes in the exchange itself was
thus also included at |t|>1 GeV2.
Figure 5.Contributions to ω-photoproduction: natural
parity t-channel exchange (left), unnatural parity π0 t-
channel exchange (middle), s-channel intermediate
resonance excitation (right).
Because of the sizeable ω→ π0γ decay (8%),
significant unnatural parity π0
exchange has been
expected for ω-photoproduction at smaller energies
(Fig.1 middle). It was indeed observed and found
dominating close to threshold. However, neither
Poimeron nor π0
exchange are able to reproduce the
strong threshold energy dependence of the cross
section and the ω decay angular distribution observed
in exclusive photoproduction and electroproducton.
This was interpreted as possible evidence for s-channel
contributions (Fig.1 right)[11].
Experimental support comes from a first
measurement of photon-beam asymmetry, Σ , through
the GRAAL collaboration[6,12].
The threshold ω-photoprodution is Eγ = 1.1 GeV; ω
meson decays mainly into channels:
0
0
( . . 89%)
( . . 8.9%)
B R
B R (1)
In Bonn, the load decay channel can be observed very
well by combining the BGO (π0) and the spectrometer
(π + π
-).
Moreover, the spectrometer allows a more detailed
study of other vector-meson such as the ρ-meson. Its
main decay modes (to almost 100%) proceed via ρ0 →
π+ π
-, ρ
+ → π
+ π
0 and ρ
- → π
- π
0 . In particular, the last
two decays that derive from the ―twins‖ reactions γ p
→ ρ+
n and γ n → ρ- p may be confused in case of the
proton inefficiency combined with neutral noise, for
this reason the BGO - spectrometer combination is
crucial.
REFERENCES
[1] F. Wilczek, hep-ph/0201222v2;
[2] G. Mandaglio et al., Phys.RevC 82, 045209(2010); [3] R. Di Salvo et al., Eur.Phy. J A 42,151 (2009);
[4] A. Fantini et al., Phys.RevC 78, 015203 (2008);
[5] B. Krusche, Czech. J. Phys. 49 (1999); [6] E. Hourany, Romanian Reports in Physics, Vol. 59, No. 2, P.
457–472, 2007;
[7] http://b1.physik.uni-bonn.de/ExperimentalSetup; [8] S. Capstick and W. Roberts, Prog. Part. Nucl. Phys. 45, S241
(2000);
[9] J. Ajaka et al., PhysRevLett. 96, 132003 (2006); [10] A. V. Sarantsev, A. V. Anisovich, V. A. Nikonov and H.
Schmieden, Eur. Phys. J. A 39 , 61–70 (2009); [11] F. Klein, PhysRevD.78, 117101 (2008);
[12] V. Vegna et al., in preparation.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
81
DIODE LASERS FOR OPTICAL TRAPPING APPLICATIONS
R. Sayeda,b,
*, G. Volpec, M. G. Donato
b, P. G. Gucciardi
b, and O. M. Maragò
b
a)Dottorato in Fisica dell’Università di Messina, Dip.to di Fisica, F. S. D’Alcontres 31, 98166 S. Agata-Messina, Italy
b)CNR-IPCF, Istituto per i Processi Chimico-Fisici, V.le F. S. D’Alcontres, 37, I-98158, Messina, Italy
c)Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, 70569 Stuttgart, Germany
* Corresponding author, e-mail: rania_sayed80@yahoo.com
Abstract
Diode lasers can be built to meet stringent
specifications on beam stability, optical beam shape,
wavelength stability, thermal stability, and compact
dimensions. Stabilization of laser frequency is essential
for various research fields such as metrology, frequency
standards, and optical communications. Here we discuss
how diode lasers can be employed in optical trapping
applications, where a laser beam is tightly focused with a
high numerical aperture objective at the diffraction limit
to trap particles near its focal spot. In this context we will
describe a novel approach to optical trapping based on
optical feedback that can be applied with low numerical
aperture lenses.
Keywords: Diode lasers, optical feedback, frequency
stabilization, optical trapping.
Introduction
Since their first use in atomic physics in the early 80's,
diode lasers have become an important part of many
modern experiments [1]. This is primarily driven by the
fact that they are compact, cost effective, small sized, and
highly efficient [2]. For the application of diode lasers in
high resolution laser spectroscopy, linewidth reduction
and frequency stabilization have been actively
investigated to improve the poor spectral quality of diode
lasers.
In principle these systems are able to achieve high
stability in their output intensity and frequency (up to
10-11
). However frequency and intensity stability are
considerably dependent on operational supply current and
on laser diode chip temperature. Thus it is crucial to
minimize fluctuations of these operational parameters. A
laser diode is very sensitive to static electricity and EM
interference. Its quality shielding and galvanic separation
of signal wires from supply wires is not useless
complication.
Our interest in diode lasers lies in their applications for
novel approaches to optical trapping and laser cooling of
nano and microparticles. The ability to exploit light forces
for the trapping and handling of microparticles was
pioneered by Ashkin [3] in the 1970‘s. Some years later
the first optical tweezers (OT) was realized [4] using a
laser beam strongly focused by a high numerical aperture
objective lens. In these systems a particle is trapped in the
focal region of the lens by the forces arising from the
scattering of light by the particle [5,6] (see Fig. 1).
Fig. 1: (left) Ray optics interpretation of optical forces on
a dielectric sphere. (a) A light-ray (red) exerts a force
(dark gray) arising from its refraction and reflection. (b)
The forces on the sphere (dark gray) due to two light-rays
(red and orange) compensate each-other at the
equilibrium position. (c) Restoring force on an axially
displaced sphere. (d) Restoring force on a laterally
displaced sphere. (right) Exemplar 2 m latex spherical
particle optically trapped in our laboratory with a diode
laser at 830nm.
Since then, OT have been extensively used for
applications in cellular and molecular biology, soft matter
and nanotechnology. In biology, OT are used to make
micro-mechanical experiments on cells and
microorganisms both in vitro and in vivo [7-9], where the
use of a near infrared wavelength (800nm-1100nm) laser
prevents photodamage and thus the death of
microorganisms and cells [9]. In physics, the ability to
apply forces in the range of pico-Newton to micro- and
nanoparticles and to measure their displacements with
nanometer precision is crucial for investigation of
colloidal and condensed matter systems [10]. More
recently OT have been also used to manipulate, rotate and
assemble a variety of nanostructures, such as carbon
nanotubes [11-13], nanowires [14,15], polymer
nanofibers [16], graphene flakes dispersed in water [17]
and metal nanoparticles [18] and aggregates [19,20]. Here
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
82
we discuss a novel application of diode laser to optical
trapping based on optical feedback-locking.
Theory and Overview
Optical Feedback. The sensitivity of the output
intensity of a diode laser to both the amplitude and phase
of external feedback is well documented [21]. The effects
of optical feedback on the behavior of diode laser have
shown that the dynamical properties of injection lasers are
significantly affected by the external feedback, depending
on the interference conditions between the laser field and
the delayed field (returning from the external cavity). The
essence of the optical feedback method is to increase the
quality factor of the laser resonator, therefore narrowing
the linewidth and stabilizing the laser's wavelength [22].
It is well known that external optical feedback strongly
affects the properties of semiconductor lasers, the
returned light into laser cavity causes variation in the
lasing threshold, output power, linewidth, and laser
spectrum. Under lasing conditions, the diode cavity is
filled with gain medium, which, to a large extent,
compensate for the diode cavity loss. It, therefore, has
substantially greater effective quality factor, and
consequently, greater influence on the laser behaviors,
than the passive external cavity. For this reason, the
following form of field equation has been adopted for a
compound cavity laser configuration, obtained by adding
an external feedback term to a standard laser equation in
complex form [21], that is:
)t(iti
0N
ti
e)t(kEe)t(E
)n(G2
1)n(ie)t(E
dt
d
(1)
Here, N n is the diode cavity longitudinal mode
resonant frequency and 0 is the cavity loss of the diode
cavity, is the laser oscillation frequency, E t is the
field amplitude, and is the transit time in the external
cavity. The last term on the right hand side represents the
external feedback and the coefficient k is related to cavity
parameters as,
/ 2 Dk c l (2)
Where c is the speed of light, Dl is the cavity length of
diode laser, and is refractive index of the active region.
The parameter defined with the facet and external
mirror reflectivities 2R and 3R as
2/1
232 )R/R)(R1( (3)
It is a measure of the coupling strength between the two
cavities. In the above expression for external feedback,
multiple reflections in the external cavity have been
neglected.
Optical Trapping. In an OT the trapping force arises
from the presence of a gradient in the intensity of the
optical field and tends to attract particles with refractive
index higher than their surrounding towards the high-
intensity regions of the field (high-field seekers), and
conversely particles with lower refractive index towards
the low-intensity regions (low-field seekers) [3-6]. Using
simple ray diagrams it is possible to provide a very
detailed picture of the physics of the trapping process,
without the need for the use of involved calculus and
electromagnetic theory. As can be appreciated from Fig.
1(a), when a light ray enters a transparent dielectric
sphere it undergoes deflection as a result of refraction at
the interfaces. Such deflection of photons that carry
momentum results in a recoil force. This force (dark gray
arrow in Fig. 1(a)) however does not trap the particle; it
only pushes the sphere away from the light. To trap an
object it is necessary to use a set of light-rays coming
from different directions. If two light-rays come from
opposite sides of the dielectric sphere at a very high angle
they can indeed trap the particle (Fig. 1(b)). It can be
easily appreciated from similar ray diagrams what
happens when the sphere is displaced both axially (Fig.
1(c)) and laterally (Fig. 4(d)) with respect to the focus. In
this cases the total force (black arrow) pushes the particle
towards the optical trap center arises.
A simple example is a highly focused laser beam. This
acts as an attractive potential well for a particle. The
equilibrium position lies near – but not exactly at – the
focus. When the object is displaced form this equilibrium
position, it experiences an attractive force towards it. This
restoring force is in first approximation proportional to
the displacement; in other words, the force in the OT is
well described by Hooke‘s law:
Fx= - Kx (x - x0) (4)
where x is the particle‘s position, x0 is the focus position,
and kx is the optical trap spring constant along x, usually
referred as trap stiffness. In fact, optical tweezers create a
3D potential well that can be approximated by three
independent harmonic oscillators, one for each of the x, y,
and z directions. In the xy-plane (perpendicular to the
direction of the beam propagation) the force is mainly due
to gradient optical forces, while along the z-direction
(along the direction of the beam propagation) the
restoring gradient force is weakened by the presence of
radiation pressure that pushes the particle away from the
focal spot.
More complex intensity patterns have been obtained, for
example, by interfering two or more light beams or by the
use of advanced techniques such as holography and time-
multiplexing.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
83
Experimental Setup
In our experiments, standard optical trapping is
generally achieved by focusing a 830 nm laser beam
(from a laser diode Sanyo DL8142-201, 150mW nominal
power) through a 100× oil immersion objective (NA=1.3)
in an inverted microscope configuration (see Fig. 2 for a
sketch). The laser power available at the sample is about
20mW and is kept constant during the optical force
measurements. Optically trapped particles (generally latex
beads with 2 m diameter) are imaged with a CCD
camera (see Fig. 1).
Fig. 2: Sketch of the experimental setup and methodology
for feedback-controlled optical trapping. (left) When no
particle is trapped the optical feedback on the diode laser
is on and the available power at the sample permits to
efficiently attract particles at the focal spot of the low
numerical aperture objective. (right) When a particle is
trapped the feedback is off and the trap works at lower
power.
For the realization of feedback controlled optical
trapping we employ a low numerical aperture objective
(NA=0.5). In fact, feedback controlled trapping may
release the stringent requirements on numerical aperture
for the operation of standard OT. In brief, in this novel
configuration (see Fig. 2) the optical feedback on the
diode laser source is controlled by the light scattering
from a trapped particle.
When no particle is in the trap, the optical feedback
from a dielectric mirror posed above the microscope
objective will increase the trapping power in the focal
spot. Instead, when a particle falls in the trap the optical
feedback will stop and trap will work at low power
preventing damage and relaxing the stringent conditions
on high numerical aperture for standard OT.
Results and Discussion
The resulting optical force in feedback-controlled
optical trapping is regulated by the response of the light
source to the optical feedback, so it is useful to study the
characteristics of diode lasers. Three diode lasers at
different wavelengths and different output power have
been studied.
0 20 40 60 80 100 120
0
20
40
60
80
Po
we
r (m
W)
Injected current (mA)
T= 18 OC
Ith
= 33 mA
I
P
Fig. 3: L.I. curve for diode laser (Sanyo
DL7140201S, 785nm, 80 mW). The measured
threshold current is Ith=33 mA.
The most important parameter of diode lasers to be
measured is the degree to which it emits light as current is
injected into the device. This generates the output light
versus input current known as the L.I. curve. As shown in
Fig. 3 the L.I. curve for diode laser (Sanyo DL7140-201S,
785 nm, 80 mW), as the injected current is increased the
laser first demonstrates spontaneous emission which
increases very gradually until it begins to emit stimulated
radiation, which is the onset of laser action. The exact
current value at which this phenomenon takes place is
typically referred to as the threshold current, Ith. It is
generally desirable that the threshold current be as low as
possible. It is one measure used to quantify the
performance of a diode laser.
The second parameter we measured is differential
external quantum efficiency of the diode laser ηD. This is
defined as the ratio between the number of photons
exiting the laser (∆P/hυ) to the number of electrons
injected per unit time into the laser (∆I/e) and it has a
typical value ranging between 0.2 and 0.7 for continuous
wave lasers.
/
/D
P hv e P
t e hv t (5)
where e is the electronic charge, υ is the frequency of the
radiation, h is the Planck constant and ∆P/∆I is the slope
efficiency of diode laser.
By measuring the output power light versus current (L.I.)
curve of the diode lasers Toptica photonics DL100 (403
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
84
30 40 50 60 70
0
5
10
15
20
25
30
Ou
tpu
t p
ow
er
(mW
)
Injected Current (mA)
T1= 20
oC
T2= 29
oC
Linear Fit of T= 20 oC
TO= 85.5 K
nm, 30 mW), diode laser Nichia NDHV310ACAE1 (417
nm, 30 mW) and diode laser Sanyo DL 7140-201S (785
nm, 80 mW), the ηD is 0.28, 0.22 and 0.65 respectively. The third parameter that has been measured is the internal
quantum efficiency of the diode laser ηI. It is defined as
the fraction of the injected carriers that recombine
radiatively and it is given by;
I
P
v t (6)
where V is the power supply voltage. ηI for diode laser
Toptica Photonics DL100 is 19 % , for diode laser Nichia
NDHV310ACAE1, 417 nm, 30 mW, is 15 % and for diode
laser Sanyo DL7140- 201S is 26 % which is calculated
from slope efficiency of the experimental L. I. curve for
each laser.
Finally the characteristic temperature of the diode laser,
To, is calculated which is defined as a measure of the
temperature sensitivity of the device and dependent on the
particular diode whose value is a measure of the quality
of the diode. Higher values of To imply that the threshold
current and external differential quantum efficiency of the
device increase less rapidly with increasing temperatures.
This means the laser being more thermally stable. Usually
To ranges from 70 K for the worst diodes to 135 K for the
best ones [23].
The ratio between the threshold values at two
temperatures differing by ∆T is given by (Ith1/Ith2) = exp
(∆T/To). The experimental work to determine the
temperature characteristic of the GaN diode laser Toptica
Photonic DL100 was made by measuring the light versus
current (L.I.) curve of the lasers at various temperatures
as shown in Fig. 4.
Fig. 4: L.I. curve at two different temperatures for
diode laser Toptica, 403 nm, 30 mW.
From the experimental work the T0 for diode laser Toptica
DL100 (403 nm) is equal to 85.5 K, T0 for diode laser
Sanyo DL 7140 201S (785 nm) is equal to 86 K and T0
for diode laser Nichia NDHV310ACAE1 (417 nm), is
equal to 137 K. These results for all diode lasers showed
good agreement with theoretical values. The diode laser
Nichia NDHV310ACAE1 (417 nm) resulted to be the
best diode laser being less sensitive to temperature
changes.
Summary
To summarize, diode lasers are perfectly suited for
optical trapping applications thanks to their low cost, user
friendly operation, long term stability in output power and
frequency. Both micro and nanoparticles (nanotubes,
nanowires, graphene) are routinely trapped and
manipulated in our optical tweezers experiments.
The sensitivity of diode lasers to optical feedback is the
crucial enabling property for feedback-controlled optical
trapping. The external optical feedback, when it is
sufficiently strong, results in a large stability of the diode
laser and it is much more easily detected than in other
lasers because of the strong dependence of the refractive
index of the diode laser active region on the carrier
density. Such novel approach will open perspective for
extending the use of light forces with low numerical
aperture lenses much increasing the trapping depth,
trapping efficiency and spatial range in experiments.
References [1] C. J. Foot, Atomic Physics, Oxford University Press, Oxford,
(2005);
[2] L. Ricci, M. Weidemuller, Opt. Comm. 117(1995)541; [3] A. Ashkin, Phys. Rev. Lett. 24 (1970) 156;
[4] A. Ashkin, et al. Opt. Lett. 11 (1986) 288;
[5] A. Jonas, P. Zemanek, 29 (2008) 4813; [6] F. Borghese, et al. Opt. Express 15 (2007) 11984;
[7] A. Ashkin, J. M. Dziedzic, T. Yamane, Nature 330 (1987) 769;
[8] M. D. Wang, et al. Science 282 (1998) 902; [9] Y. Liu, et al. Biophys. J. 68 (1995) 2137;
[10] D. Preece, et al. J. Opt. 13 (2011) 044022;
[11] O. M. Maragò, et al. Nano Lett. 8 (2008) 3211; [12] O. M. Maragò, et al. Physica E 8 (2008) 2347;
[13] P. H. Jones, et al. ACS Nano 3 (2009) 3077;
[14] P. J. Pauzauskie, et al. Nat. Mater. 5 (2006) 97; [15] A. Irrera, et al. Nano Lett. (2011), DOI: 10.1021/nl202733j;
[16] A. A. R. Neves, et al., Opt. Express 18 (2010) 822;
[17] O. M. Maragò, et al., ACS Nano 4 (2010) 7515;
[18] R. Saija R., et al. Opt. Express 17 (2009) 10231;
[19] E. Messina, et al. ACS Nano 5 (2011) 905;
[20] E. Messina, et al. J. Phys. Chem C115(2011) 5115; [21] C. Ye, Tunable External Cavity Diode Laser, (2004);
[22] B. Tromborg, J. H. Osmundsen, IEEE J. Quantum Electr., QE-20
(1984) 1023; [23] O. Svelto, Principles of Lasers, (1993).
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
85
INTERFERENCE WITH COUPLED MICROCAVITIES
R. Stassia, O. Di Stefano
a, S. Savasta
a
a) Dipartimento di Fisica della Materia e Ingegneria Elettronica,Università di Messina Viale S. D’Alcontres, 98166
S.Agata-Messina, Italy
Abstract
Here we propose an all-optical analogue of the effect of
sign change under 2π rotation based on time-resolved
optical interference in coupled optical microcavities.
Feeding the coupled-microcavity system with a pair of
phase-locked probe pulses, separated by precise delay
times, provides direct information on the sign change of
the transmitted field.
Introduction
In quantum mechanics if we want to perform a rotation
of a generic quantum state, we have to apply the operator
U(θ) = exp(-iJ·θ/2) on the corresponding ket. A rotation
by 2π radiants around the z-axis, which intuitively ought
to be equivalent to no rotation at all, multiplies the
eigenstate of J2 and Jz by −1 if j=n/2, with n integer, and
where J is the angular momentum operator. It is necessary
a rotation by 4π radians to return to its initial state. As
observables in quantum theory are quadratic in a wave
function, the change of sign cannot be detected by
ordinary experiments.
The first Gedanken experiments aimed at the
observation of the sign change of spinors under 2π
rotations were published by Bernstein and independently
by Aharonov and Susskind. These two proposed
experiments, the first involving the interaction of a spin
1/2 particle with a magnetic field, and the second
involving the tunneling of a current of free electrons,
were conceptually similar. In both cases one system was
split into two separate subsystems, one of them was
affected by an additional 2π rotation relative to the other
one, and then recombined. The first experimental
verification of coherent spinor rotation was provided by
Rauch et al. and Werner et al., both groups employed
unpolarized neutron interferometry as suggested in the
Bernstein-Gedanken experiment. Klein and Opat reported
the observation of 2π rotations by neutron Fresnel
diffraction.
The similarity of the mathematical description (that is, the
algebraic isomorphism) between spinor rotations and the
transitions between two atomic or molecular states of any
total angular momentum has been exploited to study
analogies of 2π spin rotations with different experimental
approaches that required no fermions. One other system,
where such an effect has been observed, consists of
strongly interacting Rydberg atoms and microwave
photons: after a full cycle of Rabi oscillation, the atom-
cavity system experiences a global quantum phase shift π.
We consider a system of two coupled planar
microcavities (MCs). When one of the two is excited by
an ultrafast resonant optical pulse, the energy oscillates
between the two systems until losses through the external
mirrors prevail. In such systems the coupling of the two
cavity modes can be controlled by the transmission of the
central mirror and the two resonant modes are the optical
analogs of two atomic or molecular states, which, in turn,
are isomorphic to a spin 1/2 system. We provide with this
system a concrete and conceptually simple all-optical
realization of the sign change under 2π rotations.
Two Coupled Oscillators with source term
A semiconductor planar MC is a structure formed by
high reflecting dielectric mirrors [distributed Bragg
reflectors (DBR)] on the two sides of a spacer (Sp) layer,
of physical length LC.
Here, we consider a system composed by two planar
MCs connected through a common DBR (see Fig. 1). We
assume that the two MCs have a high Q factor and that
the intracavity modes are coupled with the external field
via two partially transmitting mirrors. In the figure 2, the
dashed line represents the single mode of an empty
microcavity. The continuous line represents the splitting
in energy of the former mode when we couple two
identical microcavities. The two resonant modes are the
optical analogues of two atomic or molecular states,
which, in turn, are isomorphic to a spin 1/2 system. We
consider systems with coupling-induced splitting quite
larger than the linewidth of the individual peaks.
Figure 1: Scheme of a double microcavity
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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Figure 2: Resonant modes of (dashed line) one
empty MC and (continuous line) two coupled
MCs.
We consider excitation of the system by a Gaussian
light pulse arriving from the left of the coupled system
2
20
00 2
)tt(
)tt(
1 ee2
1)t( (1)
The calculated field intensity is shown Fig. 3. The
figure also displays (arb. units) the corresponding
Gaussian input pulse. The transmitted intensity displays a
damped oscillatory time behavior (with Rabi frequency
ΩR) originating from the combination of coherent energy
exchange between the two MCs and losses through the
external mirrors. To inspect the phase of the transmitted
field after one or two Rabi-like oscillations, we now
consider a second pulse in phase with the first one sent
from the left into the double semiconductor planar MCs.
The total input field can be expressed as,
2
21
10 2
)tt(
)tt(
12 ee2
1)t()t( (2)
The transmitted intensity is calculated for two different
physical situations as shown in Fig. 4 and 5. First we
address the case when the arrival time of the second pulse
is chosen so that the corresponding first maximum in the
transmitted field is exactly in time with the second
maximum originating from the first pulse Fig. 4. In
particular the time delay between the two pulses
corresponds to a complete Rabi-like oscillation: ΩR(t1-
t0)=2π. In this case we find that the total signal is strongly
damped due to destructive interference.
Figure 3: light field transmitted intensity inside the
cavity in function of time when is sent a single
excitation.
Figure 4: transmitted intensity calculated when a
second pulse is sent after one complete Rabi-like
oscillation.
Figure 5: transmitted intensity calculated when a
second pulse is sent after two complete Rabi-like
oscillations.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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Hence, such an abrupt damping of the signal
demonstrates that the transmitted field after a complete
oscillation acquires a π phase (minus sign). If the arrival
time of the second pulse is chosen so that ΩR(t1-t0)=4π
(see Fig. 5) the total signal gets amplified due to
constructive interference. This condition is verified when
the corresponding first maximum in the transmitted field
is exactly in time with the next (third) maximum
originating from the first pulse.
Analytical Model
The essential physical features of such a system may be
understood through a simplified analytical model. We
adopt the quasimode approach. The discrete cavity modes
(one for each MC) interact with an external multimode
field. The quasimode approximation allows us to describe
such systems analogously to a two interacting oscillators
system. In particular, we consider a system of two
coupled harmonic oscillators (the light modes of the two
coupled cavities) with an external source ε(t). The
Hamiltonian of such a system can be written as
† † † †
0 0
† *
( )
( ) ( )
H a a b b g a b b a
t a t a (3)
where a and b are, respectively, the bosonic operators
relative to the single mode in each cavity, the coupling g
depends on the reflectivity of the central mirror, and ε(t)
describes the feeding of the cavity by a classical input
beam. The resulting evolution equations for the photon
operators inside the two cavities are
0
0
( )2
2
d ii a a g b a t
dt
d ii b b g a b
dt
(4)
where <・> indicates the mean value of the operator,
and γ takes into account the damping and losses of a field
inside the structure and may be considered as a
phenomenological parameter or as obtained from the
master equation for two coupled oscillators interacting
with a zero-temperature thermal reservoir. In the rotating
frame (putting ω0 = 0), if losses are neglected (γ = 0) and
considering the input field in the cavity as a sharp pulse
sent at t = t0 we obtain
0
0
0† 2
2
0† 2
2
( )cos
2
( )sin
2
1 cos ( )
2
1 cos ( )
2
R
R
R
R
t tAa i
t tAb
t ta a A
t tb b A
(5)
where ΩR = 2g/ħ represents the Rabi frequency. We
now calculate the number of photons emerging from the
cavity on the right, <b†b>, that can be measured by a
photodetector. Inspecting the last two equations, we
observe that it oscillates with a Rabi of frequency ΩR.
Instead, we observe, as is evident from the first two
equations, that b oscillates with a double period with
respect to the light cavity population (i.e., at a frequency
equal to ΩR/2). After a Rabi period T = 2π/ ΩR, we have
<b>T = −<b>0 = -A/ħ. Such behavior is the optical analog
of the spin-1/2 system undergoing a 2π rotation in
ordinary space. In addition, if the time delay is t = 2T =
4π/R (i.e., after a 4π Rabi oscillation) then <b>T = −<b>0
= A/ħ: the two signals are now in phase and we have the
corresponding 4π rotation in a spin-1/2 system. We
observe no phase change behavior in <b†b>. The results
in this section show that the simple analytical model here
analyzed contains all the essential physics of the process
including the π phase shift after a complete Rabi-like
oscillation.
Conclusion
In this paper we proposed an all-optical analog of the
well-known sign change of the spinor wave functions
under 2π rotations. The system here investigated consists
of two planar MCs coupled through a central mirror. Here
the two modes (in the absence of coupling) play the role
of the two spin states, whereas the coupling induces a
quasiperiodic exchange of the optical excitation among
the two modes after ultrafast optical excitation. A
complete oscillation of the excitation from one mode to
the other and back is the optical analog of a 2π spin
rotation. We showed that by feeding the coupled-MC
system with a pair of phase-locked probe pulses separated
by precise delay times, we can gather direct information
on the sign change of the transmitted field after one
complete Rabi-like oscillation period. Such results were
explained qualitatively by a simplified physical model
considering two coupled damped oscillators
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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References [1] H. J. Bernstein, Phys. Rev. Lett. 18, 1102 (1967);
[2] Y. Aharonov and L. Susskind, Phys. Rev. 158, 1237 (1967); [3] H. Rauch, A. Zeilinger, G. Badurek, A.Wilfing,W. Bauspiess, and
U. Bonse, Phys. Lett. A 54, 425 (1975);
[4] S. A.Werner, R. Colella, A.W. Overhauser, and C. F. Eagen, Phys.Rev. Lett. 35, 1053 (1975);
[5] A. G. Klein and G. I. Opat, Phys. Rev. D 11, 523 (1975); Phys.
Rev.Lett. 37, 238 (1976); [6] A. Abragam, The Principles of Nuclear Magnetism (Clarendon
Press, Oxford, 1961);
[7] E. Klempt, Phys. Rev. D 13, 3125 (1976); [8] M. P. Silverman, Eur. J. Phys. 1, 116 (1980);
[9] J. M. Raimond, M. Brune, and S. Haroche, Rev. Mod. Phys. 73, 3
(2001);
[10] A. Ridolfo, S. Stelitano, S. Patané, S. Savasta, and R. Girlanda,
Phys. Rev. B 81, 075313 (2010); [11] M. E. Stoll, A. J. Vega, and R. W. Vaughan, Phys. Rev. A 16,
1521 (1977);
[12] A. Armitage, M. S. Skolnick, V. N. Astratov, D. M. Whittaker, G Panzarini, L. C. Andreani, T. A. Fischer, J. S. Roberts, A. V.
Kavokin, M. A. Kaliteevski, and M. R. Vladimirova, Phys. Rev. B
57, 14877 (1998); [13] G. Panzarini, L. C. Andreani, A. Armitage, D. Baxter, M.
S.Skolnick, V. N. Astratov, J. S. Roberts, A. V. Kavokin, M.
R.Vladimirova, and M. A. Kaliteevski, Phys. Rev. B 59, 5082 (1999);
[14] S. Vignolini, F. Intonti, M. Zani, F. Riboli, D. S.Wiersma, L.
Balet, L. H. Li, M. Francardi, A. Gerardino, A. Fiore, and M. Gurioli, Appl. Phys. Lett. 94, 151103 (2009);
[15] 28P. Yeh, Amnon Yariv, and Chi-Shain Hong, J. Opt. Soc. Am.
67, 423 (1977).
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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SPECTRAL DEPENDENCE OF THE AMPLIFICATION FACTOR IN
SURFACE ENHANCED RAMAN SCATTERING
C. D‘Andreaa,b,*
, B. Fazioa, A. Irrera
a, P. Artoni
c, O.M. Maragò
a,
G. Calogeroa and P.G. Gucciardi
a
a) CNR – Istituto Processi Chimico-Fisici, Viale F. Stagno D’Alcontres, 37, I-98158, Messina, Italy
b) Dottorato in Fisica dell’Università di Messina, Dip.to di Fisica, F. S. D’Alcontres, I-98158 S. Agata - Messina, Italy
c) MATIS, CNR - Istituto per la Microelettronica e i Microsistemi, Via S. Sofia, 64, I-95123, Catania, Italy
* Corresponding author, e-mail: dandrea@me.cnr.it
Abstract
Surface Enhanced Raman Scattering (SERS) is
characterized by a strong signal amplification (up to
108÷10
) when both the excitation and the Raman photons
frequencies match the localized plasmon resonances
(LSPR) of the nanoparticles (NPs). In order to understand
if the effective LSPR profile refers to the bare NPs or to
the resonance of NPs ―dressed‖ with the probe molecules,
we perform multiwavelength (514nm, 633nm and 785nm)
SERS experiments using evaporate gold NPs as SERS-
active substrate on which we deposited Methylene Blue
molecules (MB) that yields a resonance energy red-shift
and a broadening of the LSPR profile.
The SERS spectra at the investigated excitation
wavelengths display a different intensity ratio of the
characteristic MB band (peaks at 450 cm-1
and 1620 cm-1
)
with respect to the Raman counterpart.
In presence of MB molecules, a red shift of 50 nm in
the LSPR is observed
The enhancement of the Raman modes at the different
excitation wavelengths follows a trend similar to the
LSPR profile of the ―dressed‖ NPs, although the
maximum enhancement is found at 785nm excitation, in
spite of a LSPR peak at 600nm.
Introduction
Surface enhanced Raman Scattering (SERS) is an
ultrasensitive spectroscopy technique that allows the
detection of molecules adsorbed on noble metal
nanoparticles (Au, Ag, Cu, etc) at sub-pico molar
concentrations and enables to detect, under optimal
condition, a single molecule [1, 2].
The giant signal amplification of SERS is related to the
collective excitation of nanoparticles (NPs) conduction
electrons, the so-called localized surface plasmon
resonance (LSPR). When the frequency of incident
photons is resonant with the LSPR of NPs, an increase of
the electromagnetic (EM) fields can be obtained in the
region close to the NPs surface, called Hot spots [3]. In
particular, in SERS, when both the excitation and the
Raman photons frequencies (ωL and ωR, respectively) are
resonant with the LSPR of the NPs, the enhancement can
reach 108÷10
order of magnitude as demonstrated
experimentally [4-8] and theoretically, according to the
|E|4 approximation [9,10].
The LSPR profile strictly depends on the size/shape of
the particles, the inter-particle distance, the surrounding
medium [11,12], and the spectral dependence of both the
excitation field enhancement factor Aexc(ω) and the re-
radiation enhancement factor Arad(ω) have been observed
to be proportional to the LSPR profile, Q(ω) [4, 12]. The
spectral dependence of Q(ω) is therefore particularly
important since it determines both the best excitation
wavelength for optimal SERS detection and the re-
radiation enhancement of the Raman modes.
It is still not known, however, whether the effective
Q(ω) refers to the LSPR of the bare NPs or to the
resonance of the NPs ―dressed‖ with the probe molecules
[Qdress(ω)]. The latter is typically energy shifted and can
be much broader, according to the molecular dielectric
constant.
The LSPR profiles can be obtained easily by extinction
spectroscopy, which is the easiest and most powerful tool
to study the resonance energy of metal NPs. Differently
from the extinction spectroscopy that is a far-field
technique, SERS measurements give insight on the
―local‖ near-field (the field in the hot spots) so, detailed
comparison of the SERS enhancement factor (EF) with
the LSPR profiles of SERS-active substrates is a possible
way to understand the properties of the electromagnetic
hot spots in NPs.
To get insight on this phenomenon we carried out
multi-wavelength SERS experiments using evaporated
gold nanoparticles as SERS-active substrates on which we
deposited Methylene Blue molecules that notably alter the
LSPR profile. The SERS peaks intensities, normalized to
the Raman intensities measured on a flat gold region, and
the relative enhancement factor of the Methylene Blue
Raman modes were compared with the LSPR spectra
highlighting an additional frequency shift, not appreciable
in the LSPR profile.
Materials and methods
The gold clusters were prepared by Electron Beam
Evaporation (EBE) on SiO2.The sample was heated at
480°C and a gold amount of 1 1016
cm-2
was evaporated.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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Figure 3: Extinction spectra of bare Gold
Nanoparticles (black line) and after (blue line) the
binding of the Methylene Blue molecules. The
three colour line and box indicate the excitation
line and the corresponding Raman region of MB
for the three lasers of our apparatus.
Gold atoms arrive on the heated substrate, so they have
the possibility to diffuse over the substrate, immediately
starting a ripening process leading to cluster formation. In
order to promote the adhesion of the gold NPs to the
substrate, the clusters were covered by a thin Silicon
Oxide layer (2-3 nm) produced by RF magnetron
sputtering.
The Methylene Blue (MB) solution was prepared
mixing deionized water with the powder (Carlo Erba
Reagenti) at the concentration of 10-4
M. The samples of
gold NPs were soaked into aqueous solution of dye for
1h, then washed in water and dried in vertical position to
avoid formation of too thick multilayer of molecules on
substrates. This method guarantees that only a single layer
of MB dye remains adsorbed onto the array, as reported in
literature [3,7,13]. Extinction and SERS experiments were
carried out with a HR800 – Jobin Yvon micro-
spectrometer. For the extinction measurements, we
exploiting the white light xenon lamp embedded in the
microscope of the HR800 spectrometer. A 10X objective
was used to collect the light transmitted through the
sample and the HR spectrometer was used to acquire the
optical signal. The LSPR profile was then proportional to
the ratio between the light transmitted in absence (I0) or
in presence of NPs (INPs). For multi-wavelength SERS
measurements we coupled our spectrometer with an Ar++
(515 nm), a He-Ne (633 nm) and a diode (785 nm) laser.
In this back-scattering Raman setup, measurements were
done focusing a few tens of µW of laser power on a
submicron spot using a 100X microscope objective (NA
0.95). All the spectra were acquired with integration times
from 10 to 120 seconds and power over the range from 4
to 400μW.
Discussion
Figure 1 shows the different LSPR profiles between the
bare NPs (blue line) and ―dressed‖ NPs (black line). The
presence of a layer of Methylene Blue molecules bound to
the gold NPs substrate yields a resonance energy red-shift
of about 50 nm (from 570 nm to 620 nm) and a
broadening of 50 nm. By using the several excitation
wavelengths available in the experimental set up, we were
able to excite the ascending and the descending region of
the dressed LSPR profile Qdress(ω) (with 515 nm and 633
nm laser lines), and the out of resonance region (by using
the laser line at 785nm), where we don‘t expect SERS
effect (colour lines in Fig. 1). As shown in figure 1 by the
colour boxes relative to each excitation wavelength, the
Raman spectrum of MB extends in the 400 – 1650 cm-1
region [7, 13] with the most intense peaks at 450 cm-1
and
1620 cm-1
.
According to previous study [14], looking the
extinction profile, for the laser excitation at 515 nm we
can expect a progressive increase of the intensity of the
SERS Raman mode of MB passing from the low
frequencies to the higher, with respect to the Raman mode
in absence of SERS effect. An opposite behaviour is
envisaged for the laser excitation at 633 nm; in this
condition the 450 cm-1
bands are closer to the LSPR peak,
and then to the condition of maximum resonance.
The SERS spectra at the investigated excitation
wavelengths (fig. 2, colour lines) display, as expected, a
different intensity ratio of the 450 cm-1
and 1620 cm-1
peaks with respect to the Raman counterpart. For each
excitation wavelength, in fact, to comparing SERS and
Raman spectra and to calculate the EF, we acquired the
MB Raman modes coming from a flat gold region (fig 2,
black lines). This expedient allowed us, also, to exclude
any contributions linked to chemical bonds between gold
and Methylene blue.
Figure 4: SERS spectra of Methylene blue for 515,
633 and 785 nm excitation wavelength (colour
line) compared with the Raman counterpart
acquired on a flat gold region (black line).
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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At 515 nm (green line) the 1620 cm-1
mode is more
enhanced with respect to the peak at 450 cm-1
, but a
similar trend is also observed for excitation wavelength at
633 nm (red line). This behaviour is not compatible with
the both the LSPR profiles acquired in the extinction
measurements. This trend is extended until the near
infrared region by using an excitation wavelength of 785
nm; here the SERS spectra show a higher enhancement of
the modes at 450 cm-1
than those at 1620 cm-1
.
Comparing the intensity of the principal bands of
Methylene Blue SERS spectra with the corresponding
Raman modes, it was possible to plot the relative mode
enhancement factor versus the Raman shift for each
excitation wavelength, as showed in figure 3. In this
picture is evident the incremental behaviour of the EF for
the visible excitations: at 515 nm we have an
enhancement from 8 times for the low frequency modes,
to 30 for the bands at 1620cm-1
. In the same way, at
633 nm (central box) the modes experience an EF from
220 to 350 times.
Figure 5: Relative SERS enhancement factor for
the 515, 633 and 785nm excitation wavelengths.
The colour lines are guide for eyes.
The maximum EF was obtained for the excitation at
785 nm, and joining 4 orders of magnitude for the bands
at 450 cm-1
, and decreasing of a factor of 10 (until 3
orders of magnitude) for the higher frequency modes.
Thank to the colour lines, guide for eyes, is evident the
new behaviour extrapolated by the SERS spectra: the
maximum enhancement happens for visible-NIR region,
100 nm red shifted with respect to the peak of the LSPR
profile.
The red shift of the near-field peak energies with
respect to the far-field quantities is a well-known
phenomenon in literature. It depends to the size of the
particles, with larger particles displaying a more marked
shift [15], but there is not a complete and simple
explanation in agreement with the experimental data that
can be used for a quantitative prediction of the shift.
This work is a partial study, contribute for the PhD
annual report, but it opens the way for future
measurements and considerations. Our purpose is to
extend the number of excitation wavelength. Using 532,
560, 660 and 695 nm excitation sources we can complete
our multi-wavelength analysis and try to find the exact
position of the maximum EF, since to obtain a complete
profile to compare with the LSPR profile. At the same
time, this experimental data may be of interest for
theoretical calculations in order to clarify the connection
between the far-field and the near-field point of view of
the same effect.
Conclusion
Multi-wavelength SERS measurements were carried
out on SERS active substrates of gold evaporated
nanoclusters. The SERS intensities of the modes of the
probe molecules, the Methylene Blue, were studied and
compared with the corresponding Raman spectra.
Then, the SERS Enhancement Factor behaviour was
compared with the Local Surface Plasmon Resonance
profile of the substrate. The presence of Methylene blue
soaked on gold nanoparticles causes an energy red shift
and a broadening of LSPR profile, as known in literature,
but the maximum enhancement was obtained for an
excitation wavelength in the Near Infrared region
(785nm), in spite of LSPR peak at 600 nm. These results
open the way for further measurements and calculations
for a better understanding about the differences between
near and far field point of view, basics for a proper
comparison between the LSPR and SERS profiles, and
thus for the optimization of the enhancement factors.
Acknowledgments
We acknowledge funding from the EU-FP7-
NANOANTENNA project GA 241818 ―Development of
a high sensitive and specific nanobiosensor based on
surface enhanced vibrational spectroscopy‖ and the PRIN
2008 project 2008J858Y7_004 ―Plasmonics in self-
assembled nanoparticles / Surface Enhanced Raman
Spectroscopy on self-assembled metallic nanoparticles.‖
References [1] S. Nie and S. R. Emory, Science 275 (1997) 1102;
[2] K. Kneipp et al., Chemical Physics 247 (1999) 155; [3] G. Laurent et al., Physical Review B 71 (2005) 045430;
[4] E.C. Le Ru et al. Journal of Physical Chemistry C 112 (2008)
8117;
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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[5] H. Wang et al., Journal of American Chemical Society 127 (2005)
14992; [6] E.C. Le Ru et al., Journal of Physical Chemistry C 111 (2007)
13794;
[7] G. Xiao and S. Man, Chemical Physics Letters 447 (2007) 305; [8] M. Kall et al., Journal of Raman Spectroscopy 36 (2005) 510;
[9] K. Kneipp et al., Chemical Review 99 (1999) 2957;
[10] E.C. Le Ru et al., Chemical Physics Letters 423 (2006) 63;
[11] A. Otto, Journal of Raman Spectroscopy 22 (1991) 743;
[12] E.C. Le Ru et al., Current Applied Physics 8 (2008) 467; [13] S. Nicolai and J. Rubim, Langmiur 19 (2003) 4291;
[14] A. McFarland et al., Journal of Physical Chemistry B 109 (2005)
11279; [15] J. Zuloaga and P. Nordlander, Nanoletters 11 (2011) 1280.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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PHOTOLUMINESCENCE OF A QUANTUM EMITTER IN THE CENTER
OF A DIMER NANOANTENNA: TRANSITION FROM THE PURCELL
EFFECT TO NANOPOLARITONS
N.Finaa,*, A.Ridolfo
b, O.Di Stefano
a,, O.M.Maragò
c ,S.Savasta
a
a)Dipartimento di Fisica della Materia ed Ingegneria Elettronica,Università di Messina,
Viale F.S. D’Alcontres 31, 98166 , Messina, Italy
b) Technische Universitat Munchen, Physik Department, Germany.
c) Istituto per i Processi Chimico-Fisici, Viale F. Stagno d’Alcontres 37, 98158, Messina, Italy
* Corresponding author, e-mail: nfina@unime.it
Abstract
We present a fully quantum mechanical approach to
describe the light emitting properties of strongly
interacting plasmons and excitons. Specifically we
present calculations for ultracompact quantum systems
constituted by a single quantum emitter (QE) (a
semiconductor quantum dot) placed in the gap between
two metallic nanoparticles. Light emitted by the quantum
dot is shown to undergo dramatic intensity and spectral
changes when the emitter excitation level is tuned across
the gap-plasmon resonance. The resulting plexciton
dispersion curve differs significantly from the one
obtained via scattering experiments [1]. Our work
suggests that the strong interaction between metallic
nanoparticles and excitons can exploited for tailoring the
spectral properties of quantum emitters for the realization
of ultracompact colored and white LEDs.
Introduction
The light-matter strong coupling regime is fascinating,
as it allows nonlinear quantum optics experiments to be
done with as few as two photons, control of the direction
of emission or phase of one photon with another one, the
observation of single-atom lasing, the study and
exploitation of quantum entanglement [2].
Here we investigate the emission properties of two
Silver Metal Nanoparticles (MNP) with a Quantum Dot
(QD) between these (see Fig. 1). In particular we study
the modifications of the quantum emitter
photoluminescence (PL) induced by the presence of the
metallic nanoparticles (MNPs). We also study the
transition from the weak to the strong coupling regime.
Fig.1 Dimer nanoantenna with quantum emitter.
Entire system is embedded in an optically active
medium.
Theory
The system is schematically showed in Fig1. It is
entirely embedded in a medium with constant permittivity
bε . The expectation value of the total system polarization
is given by:
mP f a (1)
where a is the destruction operator for the localized
surface SP mode, the QD dipole moment e d ,
and the coefficient f is given in Eq. (10). The term
is the expectation value of the lowering transition
operator eg . The QE and the MNP interacts via
dipole-dipole coupling.
States g e transition is resonantly coupled with
the localized surface plasmon dipole mode with a strength
g, as showed in Fig 2.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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Fig 2. Quantum emitter two level representation:
external optical pump excites ground QD states,
giving rise to excitonic emission of light caused by
interaction with MNPs-SP.
Electrons are optically or electrically pumped from
lower levels j to upper levels i , then decay
nonradiatively to level e . Electrons finally decay by
spontaneous emission to level e .The full quantum
dynamics of the coupled nanosystem can be derived from
the following master equation for the density operator,
X sp( , )Si H L L (2)
Where SH represents the Hamiltonian terms including
free dynamics, interaction and driving, i.e.:
S 0 int driveH H H H (3)
with
† †
0 sp xH a a (4)
where x and sp are the energies of the QD
excitonic and MNP plasmonic transitions. Eq.(4)
represents the free system Hamiltonian equal to the sum
of free MNP system term with free QE term. The
Hamiltonian term describing the interaction between the
QD exciton and the quantized SP field, in the rotating
wave approximation reads:
† †
int ( )H i a ag (5)
Where:
g (6)
being
3
0
4 6 '
(8 1)Q r (7)
a field term related to the whole system, and, where:
3
3
RQ
S r (8)
with 1, 2 ,S whether the field polarization is
parallel or orthogonal to the R direction [3], while ' is a
parameter depending on SP resonance frequency. The
system excitation by a classical input field can be
described by:
† * †
drive 0 0( ) ( )H E a a E (9)
Notice that 0E is different from zero only in scattering
calculations. The Markovian interaction with reservoirs
determining the decay rates xγ and spγ for the QD
exciton and the SP mode respectively, as well as the
pumping mechanism of the QD, is described by the
Liouvillian terms, XL and spL [4]. Furthermore we
found that the term related to interaction of MNPs-SP
with incoming field is f , and it‘s given by:
3b0
48iQ 2'
(1 8 ) 3f r
Q (10)
Results
We have calculated the PL on a system with a 6nm
radius MNP at a distance R = 9.5 nm embedded in a
medium with a dielectric constant bε = 3.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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Fig.3 : Calculated dimer nanoantenna-QE PL
spectrum for different dipole moments.
In Fig.3 we can see how, on increasing the QD dipole
moment, the splitting between the two PL peaks enhances
[5]. This is due to the fact that the Vacuum Rabi Splitting
(VRS) limit is given by the following condition:
x sp(γ +γ )2
2g (11)
and, because, from Eq.(6), g is related to dipole
moment, on increasing of it, will increase the VRS, as
shown by PL spectra.
The PL spectra achieved at different distances between
the two MNPs, tuning the exciton frequency on the
resonance MNP-SP frequency, with a dipole moment μ/e
=0.7nm, are shown in Fig.4. We can see how, on
increasing the distance QE-MNP, strong coupling
plexcitonic effect, progressively, vanishes, until to show
only the QD dipole row (on R=28nm).
Fig.4 : PL spectra calculated for different
distances centered at frequency a . On
increasing distances the double peak splitting
disappears. A dipole moment μ/e =0.7nm has been
used.
The influence of MNPs on the PL of quantum emitter
has been studied in the weak coupling regime [7]. Here
we addressed the situation where the interaction between
the emitter(s) and the MNPs is so strong that a
perturbative approach fails. Figure 5 displays a series of
PL spectra taken at different exciton-SP energy detuning.
The typical anticrossing behavior, characteristic of the
strong coupling regime, can be observed. At large
detunings the PL emission is concentrated at the transition
energy of the emitter.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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Fig.5. PL spectra taken at different exciton-SP
energy detuning.
When the transition energy approaches the SP
resonance, two emission peaks are clearly visible and
emission is shared by the two polariton modes. For
comparison, Fig. 6 shows scattering spectra [6] which
display a different behavior and a different normal mode
splitting.
Fig.6. Scattering spectra as a function of the exciton
resonance.
Conclusions
We have investigated for the first time light emission
properties of QEs strongly coupled to MNPs. When
strong coupling is achieved, light emitted by the QD is
shown to undergo dramatic intensity and spectral changes
when the emitter excitation level is tuned across the gap-
plasmon resonance. The resulting plexciton dispersion
curve differs significantly from the one obtained via
scattering experiments. This work suggests that the strong
interaction between metallic nanoparticles and excitons
can exploited for tailoring the spectral properties of
quantum emitters for the realization of ultracompact
colored and white LEDs.
References [1] A. Ridolfo et al., Phys. Rev. Lett. 105, 263601 (2010);
[2] Kimble, H. J. Strong interactions of single atoms and photons in cavity QED. Phys. Scripta 76, 127–137 (1998);
[3] S.A Maier Plasmonics: Fundamentals and applications, Springer;
[4] M.O. Scully, M.S. Zubairy, Quantum Optics, Cambridge Univ.press;
[5] G.Khitrova et al. Nature Physics 2, (2006); [6] S.Savasta et al., ACS Nano 4 (11)(2010), pp. 6369 6376
[7] L.Novotny,B.Hecht, Principles of Nano-Optics, Cambridge
Univ.pres
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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LATERAL DIFFUSION OF DPPC AND OCTANOL IN A
LIPID BILAYER MEASURED BY PFGE NMR SPECTROSCOPY
S. Rificia,*
a)Dottorato in Fisica dell’Università di Messina, Dip.to di Fisica, F.S. D’Alcontres ,98166 S. Agata-Messina, Italy
* Corresponding author, e-mail: srifici@unime.it
Abstract
Lipid lateral diffusion coefficients in the system of 1,2-
palmitoyl-sn-glycero-3-phosphocholine (DPPC), Octanol
and water were determined by the pulsed field gradient
NMR technique on macroscopically aligned bilayers. The
molar ratios between DPPC and Octanol and between
DPPC and water were set to 1:2 and 1:28 respectively.
The temperature was varied between 270 K and 323 K.
Introduction
Cell membrane is the first part of the cell to be in
contact with any nutrient or pathogen in the extracellular
matrix. Biological membranes are complex mixtures of
different lipid molecules and proteins. A lipid is an
amphiphilic molecule with an hydrophilic polar
headgroup and usually two hydrophobic hydrocarbon
chains. When dispersed in an aqueous environment, lipids
self-assemble in order to reduce contacts with water. They
can arrange themselves in a variety of morphologies
depending on the structure of the lipid, the nature of the
lipid headgroup and its degree of hydration, temperature,
concentration and osmotic pressure. Multilamellar
vesicles, continuous ordered bilayers and monolayers,
liposomes and micelles are typical examples of possible
structural arrangements. [1]
Single artificial phospholipid, or simple mixtures of
artificial phospholipids have long been used as mimetic
membranes for examining the physical, chemical and
biological properties of the biomembranes. This approach
is justified by the observation that some model membrane
systems have been widely recognized as essentially
equivalent to natural systems such as those found in
myelin and erythrocyte membranes. [2]
Dipalmitoylphosphatidylcholine (DPPC) has a very
simple chemical structure, a phosphocoline (PC)
headgroup and two identical linear saturated hydrocarbon
chains, and plasma membrane contains a relatively large
amount of phospholipids with PC headgroup, this is why
DPPC is so largely used in all studies about model
membrane. Despite it has been widely studied, his
dynamics are still not well understood.
Many structural and dynamic intrinsic properties of
aqueous dispersions of lipid bilayers are governed by
temperature. In the case of phosphatidylcholines, these
phase transitions take place within the temperature range
263–353 K, depending on the strength of the attractive
Van der Waals interactions between adjacent lipid
molecules. Longer tailed lipids have more area to interact,
increasing the strength of this interaction and
consequently decreasing the lipid mobility. Transition
temperature can also be affected by the degree of
unsaturation of the lipid tails. An unsaturated double bond
can produce a kink in the alkane chain, disrupting the
lipid packing. This disruption creates extra free space
within the bilayer which allows additional flexibility in
the adjacent chains. [3]
DPPC shows three kinds of structural changes with
increasing temperature under atmospheric pressure. This
changes are thermotropic phase transitions: the sub-
transition from the lamellar crystal (Lc) phase to the
lamellar gel (Lβ′) phase, the pre-transition from the Lβ′
phase to the ripple gel (Pβ′) phase, and the main transition
from the Pβ′ phase to the liquid crystalline (Lα) phase
occur in turn with increasing temperature. [4]
The (Lα) phase is considered the most important,
because many biologically relevant processes occur in
this phase. Indeed, lamellar bilayers in the fluid phase
supply an efficient, planar permeability barrier, which still
allows functional flexibility and lateral diffusion motions
of associated membrane proteins.
Adsorption of alcohol molecules or other small
amphiphilic molecules in the cell membrane has a
destabilizing effect on its structure. Experiments on
phospholipid membranes have shown that alcohol
molecules can induce the interdigitated phase [5] that, at
high alcohol concentrations, replaces the ripple gel phase
[6,7]. A complete interdigitation is expected at alcohol
concentrations above a threshold value assumed to be
about 2:1 alcohol to lipid ratio in the membranes as it has
been observed for DPPC/n-butanol system by a DSC
study [7]. When the interdigitation occurs, lipid molecules
from opposing monolayers interpenetrating, thereby
decreasing the bilayer thickness. The increase of the polar
headgroup area, due to the addition of alcohol molecules,
gives rise to a reduction of the Van der Waals attraction
between lipid acyl chains. Bound alcohol molecules
reduce the mobility of the polar headgroups and, at the
same time, cause a decrease of the ordering and an
additional coiling of the melted acyl chains.
Concerning dynamics, different types of motions, with
correlation times ranging from picoseconds
(corresponding to the motion of lipid chain defects, for
example) to microseconds (corresponding to collective
excitations of the bilayer membrane), characterize
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bilayers, a large variety of which is essential for the
functionality of membranes [8,9,10].
Motions within the bilayer plane have been largely
studied by NMR relaxation techniques [11,12,13] and
neutron scattering [8,9,10].
Experimental details - Sample preparation
The phospholipid 1,2-palmitoyl-sn-glycero-3-
phosphocholine (DPPC) was purchased from Avanti
Polar Lipids, Octanol was purchased from Sigma Chem.
Co. Both chemicals were used without further
purification.
Aligned multilayers of DPPC with Octanol were
obtained following the preparation suggested by Hallock
[14], using mica plates as supporting substrate. Mica
substrate was covered with about 1.5 mg of lipids per
cm2. Following the cited procedure, DPPC and Octanol
were dissolved in an excess of 2:1 CHCl3/CH3OH
(chloroform/methanol). The solution was spread and dried
on the face of the substrate plate. All procedures for
sample preparation were executed in a glove box under
nitrogen gas to prevent lipid oxidation. This procedure
resulted in a thin film covering the whole area of the mica
plate. The sample was indirectly hydrated at 323 K in
96% relative humidity using a saturated potassium sulfate
D2O solution for 12 days, after which 28 mole of D2O per
mole of lipid were added. The mica plate was then placed
in a glass tube in the diffusion probe.
Nuclear magnetic resonance
Self diffusion coefficients of hydration water ( WD ),
DPPC ( D ) and Octanol ( OcD ) molecules were
measured by hydrogen pulsed-field gradient spin echo
NMR (1H-PGSE-NMR), which enables the non-invasive
measurement of molecular self diffusion coefficient over
a wide range of time scales (from milliseconds to
seconds) directly [15, 16].
PGSE experiments were performed on aligned pure
DPPC and DPPC with Octanol membranes deposited on
mica sheets. All measurements were carried out in fully
hydration condition at temperatures below, near and
above the phase transition temperature using a Bruker
AVANCE NMR spectrometer operating at 700MHz 1H-
resonance frequency. The temperature was controlled
within ± 0.5 K by a heated air stream passing the sample.
Self-diffusion measurements are based on NMR pulse
sequences, which generate a spin-echo of the
magnetization of the resonant nuclei. The method is based
on sensitising the sample to molecular translational
displacement by the application of magnetic field-
gradient pulses.
By the appropriate addition of two pulsed-field
gradients, in the defocusing and refocusing period of the
sequence, of duration δ and intensity g, separated by a
time interval Δ, the spin-echo intensity becomes sensitive
to the translational motion along the gradient direction for
the tagged molecules. These gradients, in fact, cause the
nuclear spins in different local positions in the sample to
precess at different Larmor frequencies, thereby
enhancing the dephasing process. If the spins maintain
their positions throughout the experiment, they will still
refocus completely into a spin–echo by the SE pulse
sequence. On the other hand, if they change their
positions during the experiment, their precession rates
will also change, and the refocusing will be incomplete,
resulting in a decrease in the intensity of the spin–echo.
The spin echo M(δg,Δ), is attenuated according to
2
0/ exp[ ]M M DQ (1)
where Q g and γ is the gyromagnetic ratio of 1H. Q
has the dimension of an inverse length, being a measure
of the spatial scale probed, and is equivalent to the
exchanged wave vector in a scattering experiment.
In our experiment, the mica plate with deposited DPPC
with Octanol is placed parallel to the magnetic field to
test for lateral (in-plane) diffusion. To record the decay of
the 1H components, a train of pulses at increasing gradient
strength is used.
Integration of spectral peaks was performed using the
Bruker-supplied XWIN-NMR software.
Figure 1 shows the decay of spin-echo intensities for
water and phospholipid/alcohol system as a function of
Q2Δ for three different temperatures, T=287K (triangle),
T=291K (circle) and T=295K (square). In the same
figures, the fitting curves (continuous lines), obtained
from a nonlinear fit of the Fourier-transformed peak
amplitudes according to the Equation (1), are also shown.
The data were fitted to an equation with three diffusion
coefficients. This would be the case for a system
consisting of three separated species. In fact, three decay
times are clearly visible, the faster due to water
molecules, the lower to phospholipid molecules, and the
intermediate ascribed to Octanol molecules.
The found diffusion coefficients for WD , D and OcD
are reported in Table 1.
Table 1
T=287K T=291K T=295K
2 /WD m s 103.4 10 103.8 10
105.1 10
2 /OcD m s 116.5 10 117.1 10
101.3 10
2 /D m s 127 10 125.3 10
111 10
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
99
1E8 1E9 1E10 1E11
0.1
1
DPPC+Octanol
M /
M0
Q2 Delta [m
2 sec]
T=287 K
T=291 K
T=295 K
Fit
Figura 1: PGSE intensity decay in fully hydrated
DPPC/Octanol bilayer at T=287K (triangle),
T=291K (circle) and T=295K (square). The
continuous lines are the fitting functions.
In the case of water molecules, we found diffusion
coefficients in good agreement with those measured in
PC-water systems, which are in the range of 10 21 10 /m s to
10 220 10 /m s depending on water
concentration, temperature, and bilayer composition. [17,
18,19,20,21,22].
Figure 2 shows the three diffusion coefficients as a
function of T.
It can be observed that the lateral diffusion coefficient
increases with increasing temperature; i.e. when the full
system is clearly in the liquid–crystalline phase, where
enhanced dynamics of the acyl chains are expected.
Water and alcohol molecules follow membrane
transition. Alcohol diffusion sharply lowers near the main
transition temperature, and, below the transition, it seems
that alcohol and DPPC molecules have the same diffusion
coefficient. Below the transition, Octanol and DPPC
move together, and this is an evidence of the formation of
the interdigitated phase.
Conclusions 1H-PGSE-NMR experiments provided information on
long-range lateral diffusion, up to some mm distances, of
inter-layer water, lipid and Octanol molecules.
Three decay times are clearly visible, the faster due to
water molecules, the lower to phospholipid molecules,
and the intermediate ascribed to Octanol molecules.
In the case of water, a reduction in the diffusion
coefficient alone is observed and assigned to restricted
geometry.
On the other hand, the phospholipid component shows
a novel and interesting result of a nearly constant
diffusion coefficient in the gel phase and a net increase in
mobility in the liquid–crystalline phase.
275 280 285 290 295 300 305 310 315 320
0.0
2.0x10-10
4.0x10-10
6.0x10-10
8.0x10-10
1.0x10-9
1.2x10-9
D (
m2/s
ec)
T(K)
DW
DOc
D
Figura 2: The three self diffusion coefficients of
hydration water (circles), DPPC (stars) and
Octanol (triangles) as a function of T are shown.
The self diffusion coefficient of bulk water (empty
circles) in also plotted.
Below the transition, Octanol and DPPC move
together, and this is an evidence of the formation of the
interdigitated phase.
References [1] R. Lipowsky and E. Sackmann, Handbook of Biological Physics,
Vol. 1, Elsevier Science, Amsterdam, 1995; [2] Rosser, M. F. N., H. M. Lu, and P. Dea. 1999, Biophys. Chem.
81:33–44;
[3] R. Koyonova and M. Caffrey, Biochim. Biophys. Acta 1376 (1998) p.91;
[4] N Tamai, M Goto, H Matsuki, S Kaneshina, Journal of Physics:
Conference Series 215 (2010) 012161 doi:10.1088/1742-6596/215/1/012161;
[5] J. L. Slater and C. H. Huang, Prog. Lipid Res. 27, 325-359 (1988);
[6] E. S. Rowe, T.A. Cutrera, Biochemestry 29, 10398-10404 (1990); [7] F. Zhang and E. S. Rowe, Biochemistry 31, 2005-2011 (1992);
[8] M.C. Rheinstadter, T. Seyde, L. Demmel et al., Phys. Rev. E 71 (2005) p.061908;
[9] M.C. Rheinstadter, C. Ollinger, G. Fragneto et al., Phys. Rev. Lett.
93 (2004) p.108107; [10] S. Konig, W. Pfeiffer, T. Bayerl et al., J. Phys. II (1992) p.1589;
[11] S. Konig, T.M. Bayerl, G. Coddens et al., Biophys. J. 68 (1995)
p.1871; [12] G. Oradd and G. Lindblom, Biophys. J. 87 (2004) p.980;
[13] P. Meier, E. Ohmes and G. Kothe, J. Chem. Phys. 85 (1986)
p.3598;
[14] Hallock K J, Henzler Wildman K, Lee D K and Ramamoorthy A
2002 Biophys. J. 82 2499–503;
[15] E.O. Stejskal and J.E.Tanner, J. Chem. Phys. 42 (1965) p.288; [16] H.V. As and P. Lens, J. Ind. Microbiol. Biotech. 26 (2001) p.43;
[17] Lange, Y., and C. M. Gary Bobo. 1974, J. Gen. Physiol. 63:690-
706; [18] Inglefield. P. T., K. A. Lindblom, and A. M. Gottlieb. 1976,
Biochim. Biophys. Acta. 419:196-205;
[19] Lindblom, G., H. Wennerstrom, and G. Arvidson. 1977, J. Quant. Chem. 12(2):153-158;
[20] Chan, W. K., and P. S. Pershan. 1978, Biophys. J. 23:427-449;
[21] Konig, S., E. Sackmann, D. Richter, R. Zorn, C. Carlile, and T. M. Bayerl. 1994, J. Chem. Phys. 100:3307-3316;
[22] Volke, F., S. Eisenblatter, J. Galle, and G. Klose. 1994, Chem.
Phys. Lipids. 70:121-131.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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CHEMICAL EQUILIBRATION OF THE QUARK GLUON PLASMA
F.Scardinaa,b,
*, M.Colonnab, V.Greco
,b,c, M.Di Toro
b
a)Dottorato in Fisica dell’Università di Messina, Dip.to di Fisica, F.S. D’Alcontres ,9816 S. Agata-Messina, Italy
b) INFN Laboratori Nazionali del Sud, Via S. Sofia 62, I-25125 Catania, Italy
c) Dipatimento di Fisica e Astronomia, Università di Catania, Via S. Sofia 64, I-95125 Catania, Italy
* Corresponding author, e-mail: scardinaf@lns.infn.it
Abstract
The ultra-relativistic heavy ion collisions performed at
the Relativistic Heavy Ion Collider (RHIC) and at Large
Hadron Collider (LHC) represent the fundamental tool to
study the properties of the Quark Gluon Plasma (QGP).
We have studied the evolution of the QGP created in such
collisions using a relativistic transport code which is
based on the solution of the relativistic Boltzmann
equation including elastic and inelastic two body
collisions between partons. We have focused our attention
on the chemical equilibration of the QGP. In fact such
equilibration is a fundamental step to deal with before to
analyze hadronization. We have performed calculation in
a box at equilibrium in order to check the code and finally
we have performed simulation for the collision in both
RHIC and LHC case. The purpose of our work is to show
how the QGP, which is initially composed for mostly by
gluons, go towards chemical equilibrium with a
consequent enhancement of the quarks number. Moreover
we have studied the dependence of the chemical
equilibration from the transverse momentum pT. We have
observed that at the end of the evolution of the fireball
the ratio Nq/Ng in the region of low pT reach the
equilibrium value of 2.25. The presence of a such large
amount of quarks should modify the background for the
various energy loss scenarios. The ratio between the
quark number and the gluon number in the region of high
pT do not reach the equilibrium value but is significantly
different from the initial value. This difference should
explain the relative abundances of the hadrons that
coming from the fragmentation of high pT partons.
INTRODUCTION
We have studied the evolution of the QGP created in
ultra-relativistic heavy-ion collision with a relativistic
transport code based on the numerical solution of the
relativistic Boltzmann. Using such code we have studied
the chemical equilibration of the QGP created at RHIC
and at LHC. The analysis of such equilibration assume a
fundamental importance in order to have a comprehension
of the abundances of the different species of hadrons
revealed in the experiment. Moreover we want to improve
the description of the QGP using an effective kinetic
theory for a quasi-particle model. In such model the
particle acquire an effective mass and this causes a
further enhancement of the quark number.
TRASPORT APPROACH
We have studied the evolution of the Quark Gluon
Plasma using a relativistic transport simulations based on
the solution of the Boltzamann equation.
22( , )p f x p C (1)
Where f(x,p) are the partons distributions functions and
C22 is the collision term.
' '
3
222 3
1 2
3 ' 3 '' '1 2
1 2 1 23 ' 3 '
1 2
24 4 ' '
1 2 1 212 12
1 1
2 (2 ) 2
( )(2 ) 2 (2 ) 2
(2 ) ( )
d pC
E E
d p d pf f f f
E E
M p p p p
(2)
υ is set equal to 2 if 1 and 2 are identical particles.
For the implementation of the collision integral we use
the so called stochastic algorithm[1,2]. In such algorithm
if the collision will happen or not is sampled
stochastically comparing the probability of the two body
collision with a random number between 0 and 1.
2 2
22 22 3
1 2
collrel
N tP v
N N x (3)
If the extracted number is less than the probability the
collision will occur. In the limit Δt ->0 Δx->0 the
numerical solutions using the stochastic method converge
To the exact solution of the Boltzamann equation. So it
is important to divide the space into sufficient small cells.
We consider both elastic and inelastic collision using
the differential cross section indicated in the following
formulas [1,3]
2
2 2 2 2
2
( )
gg gg
s
T T D
d
dq q q (4)
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
102
2
2 2 23 ( )
gg qq
s
T T q
d
dq s q m
(5)
2
2 2 2
64
27 ( )
gg qq
s
T T q
d
dq s q m (6)
Where qT is the transverse component of moment
transfer, mD and mq denote respectively the Debye mass
for gluons q and quarks respectively.
Calculations In a Box at equilibrium
With the purpose of demonstrate the correct operation
of our code we have chosen some situation in which the
outcome are known analytically. Hence we have
performed ―box calculations" in which a particle
ensemble is enclosed in a box, with fixed limits, and
evolve dynamically until an appropriate final time.
Initially particles are distributed homogeneously within
the box and their momentum is chosen highly anisotropic
( 6 ) ( )T z
T z
dNp GeV p
Ndp dp (7)
After a sufficiently long time the system equilibrate as
shown in fig. 1. For a classical, ultrarelativistic ideal gas
the energy distribution has the Boltzmann form
/
2 3
1
2
E TdNe
NE dE T (8)
In figure 1 the time evolution of the energy distribution
for such box calculations is depicted the size of the box is
125 fm3. We have considered anisotropic calculations and
we have taken a constant cross section of mb. The
final time is 3 fm/c. Moreover in order to improve
statistics we have used 50 test particles for one real. The
dotted line in the figures indicate the analytical
distribution with temperature T=2 GeV calculated using
The following formula
3 T (9)
Where the energy density and the particle densities are
given by the initial conditions. We see a good agreement
between the numerical results and the analytical
distributions.
As we can observe from the figure our code reproduce
analytical results. In order to have sufficient argument to
guarantee whether our algorithm operating correctly is
necessary to check other quantity, as for example the time
evolution of momentum anisotropy shown in fig. 2 and
defined as the average transverse momentum squared
over the average longitudinal momentum squared. The
initial conditions in this case are set to be the same as in
fig 1.
Figure 1:Temporal evolution of energy distribution
of a system consisting of N=2000 massless
particle in a fixed box whose size are 125 fm3
Figure 2: Time evolution of the momentum anysotopy
from box calculations. The initial conditions are set to be
the same as in Fig. 1
Once we have checked that our algorithm reproduce the
analytical calculation relatives to kinetic equilibrium we
have checked that also the chemical equilibrium of the
plasma can be reproduced by our algorithm.
For massless case the ratio between the number of
quark and the number of gluon is simply given by the
ratio between the respective degrees of freedom υ
q q
g g
N
N (10)
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
103
where υq=2*3*Nf υg = 2*8. In our case we consider two
flavour and thus the ratio between the number of quark
and the number of gluons is 2.25. The results are shown
in fig.3
Figure 3:Time evolution of the gluon and quark
number in box calculations. We have considered
gluons and quarks with three flavour as parton
species
Results for the heavy Ion collision
We have performed simulations for heavy-ion
collisions for both RHIC (200 AGeV) and LHC (5.5
ATeV). In figure 4 are shown the ratio between the
number of quark and the number of gluons as a function
of transverse momentum. The dot line indicate the initial
ratio while the thick line and the dashed line indicate the
final ratio obtained at RHIC and LHC respectively. We
can observe that for both RHIC and LHC at low
transverse momenta the ratio is near to the equilibrium
value. Moreover at LHC where the evolution time is
longer also at high pT the ratio is different from the initial
one
Figure 4: Ratio between the quarks number and
the gluon number as a function of pT
EFFECT OF THE MEAN FIELD
We have the intention to introduce in our code the
effect of the mean field using a quasi-particle model [4].
In such a model the interaction is encoded in the quasi
particle masses and once the interaction is accounted for
in this way the quasi particle behave like a free gas of
massive constituents.
The effect of the masses on the chemical equilibration
of the plasma is substantial.
In the massive case the ratio Nq/Ng depends on the
temperature as can be calculated in the following formula
2
2
/
2
2
/
q
g
q T
q qm T
q q
g gg T
g gm T
md e
TN
N md e
T
(11)
Where
2 2 2 21 1;q q g gm p m p
T T (12)
The expected ratio is indicated in fig. 5. In this figure
we can observe that the value of the ratio is strongly
dependent from temperature and that at the freeze-out
temperature the ratio reach the value of 6.3 that is larger
that the value obtained in the massless case.
Figure 5: ratio Nq /Ng as a function of temperature
calculated using the formula 0.8
Conclusions
The Quark Gluon Plasma created in heavy-ion
collisions seem to reach chemical equilibrium at low
transverse momentum, but in the case of LHC also at
high pT the ratio is significantly different from the
initial one. Thus at the end of its evolution the number
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
104
of quark in the plasma is greater than the number of
gluons and this have two important implication: first of
all the background of the energy loss process is
significantly modified and moreover the abundances of
the different species (pion, proton , kaon) coming from
the fragmentation of quarks and gluons are significantly
affected by the increasing of the quarks number. In the
region of high transverse momenta this effect must be
analyzed in order to have a better comprehension of
the different suppression experienced by the hadronic
species and have to be compared with the results of the
[5,6,7].
We have moreover the intention to include the effect of
the mean field in order to give a better description of
the QGP. This will be done using a quasi-particle
model.
We expect that the effect of the masses will increase the
ratio between the quark number and the gluon number
up to 6 for the region of low pT . This implicate that the
bulk should be for mostly composed by quarks.
REFERENCES
[1] Z. Xu , C. Greiner, Phys. Rev C.71 (2005) 064901;
[2] G. Ferini , M. Colonna, M. Di Toro and V. Greco, Phys. Lett. B
670, 325 (2009); [3] J. F. Owens, E. Reya, and M. Gluck, Phys. Rev. D 18, 1501
(1978);
[4] S. Plumari, W M. Alberico, V. Greco, C. Ratti, arXiv :1103.5611 [hep-ph];
[5] F. Scardina, M. Di Toro, V. Greco, Phys. Rev. C 82 (2010)
054901; [6] W. Liu, C. M. Ko and B. W. Zhang, Phys. Rev. C 75 (2007)
051901;
[7] F. Scardina, M. Di Toro, V. Greco, Nuovo Cim. C34N2 (2011) 67-73.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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A STUDY ABOUT DYNAMIC MODELS ON PHOSPHOLIPIDS
A. Trimarchia,*
a)Dottorato in Fisica dell’Università di Messina, Dip.to di Fisica, F.S. D’Alcontres ,9816 S. Agata-Messina, Italy
* Corresponding author, e-mail: antotrimarchi@unime.it
Abstract
Model membranes are a first step to understand very
complex objects like cell membranes. The former
constitute a essential element so that cells work.
Membranes are active protagonists in many processes, as
material transport and cell signaling. The comprehension
of the dynamics in play can give us the possibility to
exploit them in several research fields like pharmaceutical
industries or medical sciences. In this paper we try to
explain some membrane motions by applying several
models to the elastic incoherent scattering factor (EISF)
like the spherical diffusion or the uniaxial rotation and we
show the results.
Introduction
Membranes are an essential part of the living organisms,
playing a fundamental role in several tasks[1]: they
surround cells separating them from the external
environment. They are composed of amphipathic
phospholipids: a hydrophilic head and one or two
hydrophobic chains. In a biological membrane there are
many different types of lipids as well as many other
components besides them, like the proteins, that have
important tasks as surface recognition, cytoskeleton
contact, signaling, enzymatic activity, or transporting
substances across the membrane. Membranes are an
important site of cell-cell communication. The complexity
of these objects makes their study very difficult so we
approximate them with more simple structures,
phospholipid bilayers. Phospholipids undergo phase
transitions in the temperature range from -10 to 80 °C; the
main phases belonging to bilayers are the gel phase where
the chains are stiff and well ordered, and the liquid phase
where the chains are quite disordered. The structures that
these phospholipids can form are several ones, depending
on lipid concentration, temperature, pressure, and the
presence of other substances: they can form bilayer
structures, spherical structures, like liposomes, or
micelles[2,3]. Dimensionally, important structural
quantities to characterize a phospholipid bilayer are the
lamellar repeat spacing D, the hydrocarbon chain
thickness 2Dc and the average area per lipid A. NMR, X-
ray and neutron diffraction[4-6] techniques provided
several information about form factors, electron density
and scattering length density profiles, while further
information and confirmations to experimental models are
been obtained by simulations[7]. Nowadays membranes
are objects of studying for several research fields and
applications[8,9]. In this paper we focus our attention on a
QENS study of DMPC(1,2-dimyristoylsn-glycero-3-
phosphatidylcholine), and POPC (1-palmitoyl-2-oleoyl-
sn-glycero-3-phosphocholine) phospholipid bilayer, in
order to investigate dynamics.
Experimental details
SAMPLE PREPARATION
DMPC and POPC powder sample were purchased from
Avanti Polar Lipids. The samples were prepared in order
to obtained aligned multilayers following the preparation
suggested by Hallock et al.[10]. The lipids were dissolved
in a solution 2:1 CHCL3/CH3OH (chloroform/methanol).
After drying the lipid solution, it was joined to a solution
2:1 CHCL3/CH3OH containing a 1:1 molar ratio of
naphthalene (C10H8) to lipid so that for each mg of
substrate the lipid was dissolved again in 15 μl of this
solution. This solution was applied on only one face of
the mica sheets, so that we spreaded about 1,5 mg of lipid
per cm2. Naphthalene and any residual organic solvent
were removed by means of a vacuum drying overnight.
Hydration at 40 °C in 96 % relative humidity was
indirectly performed using a saturated potassium sulfate
D2O solution for 12 days, after which 28 moles of D2O
per mole of lipid are added. Each sample was then built
up stacking 6 substrate plates piled with the last foil not
spreaded, and was equilibrated at 4 °C for 12 additional
days. The alignment was then verified by 31
P-NMR
chemical shift and with X-ray diffraction.
SPECTROMETER
The IN5, time of flight (TOF) spectrometer, at ILL
Facility (Grenoble), has been used to perform neutron
scattering measurements on the phospholipids.
This instrument is used to study low-energy transfer
processes as a function of momentum transfer, typically,
in the region of small energy and momentum transfer
values, with an energy resolution of the order of δE/E =
1% (e.g. quasi-elastic scattering in solids, liquids,
molecular crystals and inelastic scattering with small
energy transfers in the order of magnitude 0.1-250 meV).
It is characterized by a primary spectrometer in which two
synchronized choppers are used to define the incident
beam energy, while a third chopper removes unwanted
neutrons. A fourth chopper, finally, turning with lower
velocity, avoids different pulse overlap. Samples, usually,
were run in two orientations for the normal to membrane
plane and beam direction.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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At θ = 135°, the dynamics are mainly probed in the
membrane plane. All scans have been performed starting
from an equilibrated liquid crystalline phase hydrated
with 28 D2O molecules per lipid.
Figure 6:Data fits of DMPC sample at 307 K and
POPC sample at 298K in 135° orientation. Data
have a resolution of 37μeV. Spectra representation
is in logarithmic scale to better display
lorentzians.
DATA ANALYSIS
Experimental data have been collected on IN5 at a
resolution of 37 μeV and with a wavelength λ =8Å. We
have measured DMPC+28 D2O multi bilayer sample at T
= 307 K and POPC+28 D2O multi bilayer sample at T =
298 K and both are in liquid phase. Both measurement
have been performed in the 135° orientation that gives us
information about in-plane motions. Treatment data have
been executed with LAMP software, in order to remove
bad spectra, correct cross-sections and rebin in energy the
time of flight obtained data; afterwards they have been
fitted by performing a linear least-square analysis and
using Minuit program.
The line shape is well represented by the sum of a Delta
function and three Lorentzian functions convoluted with
the instrumental resolutions. We have assumed as fit
parameters the areas of the four functions and the half
width at half maximum (HWHM) of the three lorentzian
curves:
21 2 2 2
2
3 43 42 2 2 2
3 4
( ) ( )I A A
A A
(1)
It is interesting to notice that this model fits very well
the experimental data as it is clear from the Figure 1
where a semi logarithmic plot is displayed to put the
emphasis on residues.
From fit parameters of DMPC and POPC it is evident
as the A1, the area of the Gaussian curve (Figure 2), is
decreasing with Q. This means that in both case, the
dynamics is confined. Furthermore, the HWHMs of the
two phospholipids shows us three different dynamics
belonging to systems, in so far occur on different time-
scales and the specific rates of each one differ from other
ones at least an order of magnitude (Figure 3).
From the areas with several mathematical passages, we
can obtain the EISFs of the three motions for the two
systems; in particular the fast motion EISF can be
obtained easily like 1-A4. Several models can be used to
fit these quantities and obtain information about dynamics
concerning the sample and its spatial displacement.
Figure 2: POPC areas: the A_1 component (Delta
contribution) highlights a confined dynamics.
EISFs have been fitted with suitable models by means
of Mathematica® software.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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Figure 3:HWHM of the three motions. Diffusion
(dark points) and rattling motion (blue points).
EISF corresponding to the first lorentzian with HWHM
= 10-12 µeV can be considered to belong to a diffusion
of the atoms around their position[11]. The motion
characterized by a HWHM of about 2000 µeV is believed
to be a fast rotation, called also rattling motion around the
molecule axis. The model applied to the corresponding
EISF is the uniaxial rotation model[12]:
2 2
0
(2 1) ( ) ( )m m
m
EISF m j QR S (2)
where
0
( )2sinh
(cos )exp( cos )
m
m
S
P d
(3)
is an order parameter e Pm is the Legendre polynomials
of order m.
The δ parameter provides information about how the
motion of the atom has a distribution in a direction:
greater the parameter, more directional the
distribution[13]. A limit case is δ = 0 that corresponds to
an uniform distribution.
The EISF concerning the HWHM of about 100 µeV is
not quite clear yet, and other studies are requested to give
it an accurate meaning.
For the experimental setup specifications, free diffusion
of lipids is too slow to be observed, and it is hidden inside
the experimental resolution. In literature, there are several
models to explain these motions. The slow motion is
considered like a diffusion in a restricted volume or, or
like a ballistic motion with a long range transport on a
nanometre scale with a Gaussian-like model[14-16]. The
fast motion is considered like a rattling motion [15], while
the intermediate dynamics is thought like a kink motion, a
combination of a rotation plus an out of plane
diffusion[14].
Experimental results
From the above relations the shape of the three EISF
can be determined (Figure 4).
A comparison between POPC and DMPC EISFs (in
particular in Figure 5 diffusion EISF) shows as for all
three motions the POPC structure factors are always
higher than DMPC ones. This means POPC is
characterized by a dynamics slower than DMPC one;
hypothesis about this experimental fact can be ascribed to
acyl chains more long in the POPC, and then a more
molecular weight; the presence of a double bond between
carbon atoms in one of this POPC chain could likely
entail a decreased mobility of the whole system.
Figure 4: EISF of the motions concerning the
hydrogen atoms of the fatty acid chain of POPC.
The EISF corresponding to rattling motion is displayed
in Figure 6 with the fit curve. The formula (2) was cut off
after sixth order to calculus limits of the computer used to
run Mathematica. The value of R in the formula was
inserted like a constant and equal to the C-H bond length:
R = 1.1 Å. The formula was modified with the adding of a
normalization parameter, A, to have at Q = 0 Å-1
an
unitary value of EISF. The model fits quite well both
EISF samples and provides for the parameters the
following values; for DMPC sample, δ = 2.45, A =
0.1997, while for POPC sample, δ = 1.95, A = 0.248. In
the case of DMPC, the experimental points from Q = 1,4
Å-1
to 2.2 Å-1
have been adding from DMPC data obtained
in an experiment with wavelength λ = 5 Å. The fit results
tell us that the distribution is quite uniform, in particular
for the DMPC sample.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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Figure 5: EISF comparison between POPC and
DMPC samples
Figure 6: Fit of the EISF of the rattling motion
with the uniaxial rotation model.
Conclusion
This work has highlighted like our phenomenological
model fits very well experimental data bringing out the
presence of three distinct motions that involve hydrogen
atoms of the phospholipidic hydrophobic chains: an
hampered rotation, that we can indicate like a rattling
motion, of the hydrogen atom around its position. The
other two motions need further studies and the application
of other models to be identify with more clarity. The
phenomenological model which we have proposed to fit
data has provided similar results to other ones available in
bibliography[13-18]. The uniaxial rotation model applied
to the EISF of the rattling motion gave us information
about its distribution width. Successive studies will deal
with investigations in normal direction to the membrane
(45° orientation) and evaluations of these motions at
different temperatures to observe, i. e., how dynamics
behaves in the gel phase. A further study will take in
consideration the interdigitation of alcohols between
phospholipids in order to observe their influence on this
system.
References [1] R. Lipowsky, E. Sackmann. (1995) Structure and Dynamics of
membranes: from cells to vesicles. Handbook of Biological
Physics, Vol 1;
[2] Jain, M., Introduction to Biological Membranes, 2nd ed.,
John Wiley & Sons, New York, 1988;
[3] Gennis, R.G., Biomembranes. Molecular Structure and
Function, Springer-Verlag, New York, 1989; [4] G. Buldt et al., J. Mol. Biol., 134, 673, 1979; [5] G. Zaccai et al., J. Mol. Biol., 134, 693, 1979;
[6] J. N. Sachs et al., Biophys. J., 100, 2112, 2011;
[7] I. Z. Zubrzycki et al., J. Chem. Phys., 112, 3437, 2000;
[8] Immordino ML, Dosio F, Cattel L., Int. J. Nanomedicine 1 (3)
(2006) 297–315;
[9] Dagenais, C. et al., Eur. J. Phar. Sci., 38(2) (2009) 121-137; [10] K. J. Hallock et al., Biophys. J., 82, 2499, 2002;
[11] V. F. Sears, Can. J. Phys. 45, 237 (1967);
[12] B. F. Mentzen, Mater. Res. Bull., 1987, 22, 337; [13] M. Bee, Quasielastic Neutron Scattering; Taylor & Francis: 1988;
[14] Sackmann, E., Konig, S., Pfeiffer, W., Bayerl, T., Richter, D., J.
Phys. II France 2 (1992) 1589-1615; [15] Busch, S., Smuda, C., Pardo, L. C., Unruh, T., J. Am. Chem. Soc. ,
2010, 132 (10), pp.3232-3233;
[16] Konig S., Sackmann E., Richter D., Zorn R., Carlile C., Bayerl T. M., J. Chem. Phys. 100 (1994) 3307-3316;
[17] Konig, S., Bayerl, T. M., Coddens, G., Richter, D., Sackmann, E.,
Biophys. J. 68 (1995), 1871-1880;
[18] Pfeiffer, W., Henkel, T., Sackmann, E., Knoll, W., Richter, D.,
Europhys. Lett., 8 (2), pp. 201-206 (1989).
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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ULTRAFAST OPTICAL CONTROL OF LIGHT-MATTER INTERACTION
AND OF WAVE-PARTICLE DUALITY
Rocco Vilardia,*, Salvatore Savasta
a
a ) Dipartimento di Fisica della Materia e Ingegneria Elettronica, Università di Messina, I-98166 Messina, Italy
* Corresponding author, e-mail: rvilardi@unime.it
Abstract
A recent article [1] theoretically demonstrated the
possibility of an ultrafast control of the wave-particle
duality. It exploits a three-level quantum system strongly
coupled to a resonant microcavity. The proposed ultrafast
optical control can be experimentally realized availing
oneself of many different quantum systems ranging from
Cooper pair boxes to intersubband polaritons, from
semiconductor quantum dots to atomic physics. By
sending an opportune sequence of external probe and
control pulses it is shown that it is possible to induce a
fast coherence sudden death but also it‘s a coherence
sudden birth.
Here we theoretically study that process in deeper
detail demonstrating that the lost first order coherence is
transferred to higher order coherences. Thanks to this
process it is, therefore, possible to successively recover
first order coherence.
We also discuss a new homodyne-like scheme which
exploits phase-locked probe pulses in order to
experimentally study the wave-particle duality of the
considered quantum system and wave particle duality is
easily probed just revealing the photons escaping the
microcavity.
Introduction
The principal aim of quantum information science and
technology is the control over the modalities of
interaction between single photons and individual
quantum emitters [2-4]. Thanks to the usage of
microcavities, under opportune experimental conditions
the strength of the interaction between the quantum
emitter and the electromagnetic interaction cavity field
can be so intense that light quanta can be absorbed and
reemitted many times before escaping the cavity [2,5-9].
In such cases the physical system enters strong coupling
regime under which hybrid light-matter quasiparticles
arise.
Nowadays strong coupling can be achieved and
exploited in many experimental physical system ranging
from circuit QED [10,11] to atomic systems [12], from
quantum dots [13] in optical microcavities to microcavity
embedded quantum wells [14]. Moreover, recent studies
show the possibility to achieve the so called ultra strong
coupling regime. For all these systems, it is important to
be able to switch to and from weak coupling regime and
to be able to control the time evolution of coherences.
A recent article points out the possibility to ultrafast
switch on and off the strong coupling regime depending
on the order and on the particular times at which pulses
are sent [1]. In particular it is demonstrated that not only
some internal degrees of freedoms can be in strong
coupling while others are in weak coupling regime but the
same degree of freedom can show a mix of both weak
coupling and strong coupling features. Another important
achievement of such an article is the demonstration of an
ultrafast technique for erasing the first order photonic
coherence explaining such a phenomenology in terms of
the fundamental quantum complementarity principle
directly connected to the information one can achieve
about the quantum physical system.
In such an article it is studied the same quantum system
discuss in [1]: a single-mode microcavity containing a
quantum emitter modeled as a three level fermionic
system. The center of the presented research is the study
of the modalities of exchange of information between
different internal degrees of freedom of the same quantum
system and the study of a particular way for controlling
and testing the wave-particle duality.
In order to conduct our studies we availed ourselves of
computational simulations and of a analytical
calculations.
Theoretical model
The point of reference of our theoretical study is the
master equation for the density operator
[ , ]i H L (1)
where the total Hamiltonian H is
0 I inH H H H (2)
being
†
0 ,
,1,2
j j j a
j g
H a a (3)
†
1,2 . .IH g a H c (4)
and
* *
,1( ) ( ) . .in p c gH t a t H c (5)
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
110
a and , respectively are the
destruction operator for the single cavity mode and the
transition operator of the levels of a quantum emitter.
( )p t represents a Gaussian coherent probe pulses
resonant both with the g e transition and with the
single cavity mode. ( )c t is a control pulse resonant
with the s g transition (see the schemes in figure
1)
The realized computational simulations the adopted
parameters are: light-matter coupling constant
85g eV , cavity damping 20a eV , damping
of the ―g‖ level 2g eV , damping of the ―e‖ level
5e meV , pure dephasing of the ―g‖ level
0d
g eV , pure dephasing of the ―e‖ level
0d
e eV , 2 2.28e g meV .
Figure 1 left: The quantum emitter is theoretically
represented by the following three level scheme.
The fundamental quantum state is s . The first
and the second excited states respectively are g
and e : they respectively are the ground state
and the first excited state of the g e transition
energetically and strongly coupled to the probe
pulse. On the other hand, the s g transition is
energetically resonant with the control pulse.
Figure 1 right: Microcavity scheme. The quantum
emitter (green sphere) is placed within the
microcavity which can be externally pumped with
probe and control pulses.
Transfer of coherence
In order to study the temporal evolution of the general
quantum state we imposed that the initial quantum state is
0 s : the microcavity is empty while the quantum
emitter is in its fundamental state. A probe pulse is sent
to the microcavity. Because it is energetically resonant
with the single cavity mode, the cavity photon population
abruptly reaches a maximum after which it monotonically
decays due to cavity losses. A control pulse is sent in
correspondence to the second successive minimum.
Because it is energetically resonant with the s g
transition, its arrival determines the complete population
of the ―g‖ level. Because of the fact that g e transition
is energetically resonant and strongly coupled to the
single cavity mode than the cavity photon population †a a shows characteristic vacuum Rabi oscillations
which are also showed by the squared modulus of its
coherent part 2
a . By sending another identical
control pulse in correspondence to a minimum of †a a ,
†a a continues to perform its oscillations while 2
a
vanishes. As explained in [1] such behaviour is
explainable thanks to the fundamental quantum
complementarity principle (see figure 2).
Figure 2: (Panel a) After the first control pulse
both the cavity photon population †a a (black
dotted line) and the squared modulus of its
coherent part 2
a (continuous red line)
immediately raise for then monotonically decays
due to cavity losses. After the first control pulse
strong coupling starts and both begin to oscillate.
Cavity photon population continues to oscillate
also after a second control pulse sent in
correspondence to a minimum. On the other hand, 2
a vanishes. (Panel b) Where 2
a vanishes
2
sga oscillates. Before the second control
pulse such coherence was zero but for a short time
in correspondence to the arrival of the first control
pulse.
The zeroing of the 2
a poses a natural question.
Where does the information relative to the first order
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
111
photonic coherence go? Is it lost? Is it transferred? And
whereto? For trying to investigate such problematic, it is
useful to send a third identical control pulse in
correspondence to a minimum of †a a . The cavity
photon population continues to exhibit vacuum Rabi
oscillations while the 2
a shows a sudden rebirth and
begins to oscillate too. Such phenomenology clearly
highlights the fact that the lost-and-then-found first order
coherence is transferred to other internal degrees of
freedom. The question is now: ―Where is it transferred?‖
A detailed analysis of higher order coherences allows to
find the answer. There exist a coherence which is zero
before the arrival of the second control pulse and after the
third (it is not zero for a small time in correspondence to
the first control pulse) and which oscillates between the
second and the third control pulse. Such coherence is 2
sga . The amplitude of its oscillation is exactly that
2
a would have showed if it would have not suddenly
died due to the arrival of the second control pulse.
This analysis leads to the conclusion that 2
a and
2
sga exchange their behaviour. In other words, the
information relative to 2
a is transferred to other
internal degrees of freedom (see figure 3).
Figure 3: If a third control pulse is sent in
correspondence to the minimum of the cavity
photon population then †a a continues to
oscillate while 2
a shows a sudden rebirth and
2
sga suddenly dies.
The transfer of coherence is a general mechanism.
Sending, for example, the third control pulse in
correspondence to maximum of the cavity photon
population, †a a begins to monotonically decay and
2
a remains zero. In this case, the coherence is
transferred to 2
sga before the first control pulse
while, after it, it is transferred to 2
sga which exhibit
a monotonic decay. Such a behaviour is really important
because it testifies that the transfer of coherence takes into
consideration the effects of the modifications induced by
external pulses (see figure 4).
Figure 4: If the third control pulse is sent in
correspondence to the maximum of the cavity
photon population then †a a monotonically
decays, 2
a continues to be zero, 2
sga
oscillates between the second and the third control
pulse and the 2
sga monotonically decays
after the third control pulse.
Homodyne test of wave-particle duality
a is not a physical observable. For this reason, in
order to study such property we need indirect
measurement. To this end, it is possible to exploit an
homodyne technique by which ultrafast testing the wave-
particle duality exploring an additional degree of
freedom: a relative phase between two phase-locked
probe pulses sent after an initial control pulse [14,15].
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
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2
1
2
2
2
2
( )( ) exp( ) exp
2
( )exp[ ]exp
2
P a
t tt A i t
t tB i
(6)
After a control pulse and a successive first probe
pulse at 2 0.14at , the cavity photon population
rapidly raises and soon after beginning to oscillate. If a
second probe pulse is sent in correspondence to a
maximum of †a a at 2 0.88at with a relative
phase 0 destructive interference is observed. If,
instead, the relative phase is constructive
interference is observed. If between the two phase-locked
probe pulses it is sent a control pulse then no interference
is observable (see figure 5).
Figure 5:A control pulse is followed by two phase-
locked probe pulse. After a second probe pulse
sent with a relative phase 0 , destructive
interference is observed. If the relative phase is
then constructive interference is obtained. If
between the two phase-locked probe pulse it is
sent a control pulse then no interference is
observed.
In other words, thanks to homodyne-like measurement we
can access to information relative to inference also in a
physical observable which intensity is. After having
observed what happens in three specific cases in which it
was imposed that the relative phase is either zero or ,
we studied the phenomenology with a continuous
variation of the relative phase (see figure 6 and 7).
Figure 6: (Left) The probe pulse is sent at the first
cavity photon population maximum and
intereference is seen in the degree of freedom.
(Right)The same happens if the second probe
pulse is sent at the second cavity photon
population maximum. but for a phase with
respect to that showed in figure 6 left and in
agreement with [16].
The three three-dimensional figures thus obtained clearly
testify the presence or absence of interference in the
degree of freedom.
Figure 7: No interference is observed if a control
pulse is sent betweeen a the two probe pulses.
If the second control pulse is sent in correspondence to
a cavity population maximum then 0ec t
2 2( ) 1 0gt c t g d t s (7)
The temporal evolution operator †
pU b a1 is such
that the general quantum state after the first three pulses is
2
( ) 1 0
1 0
g
t
p e
t c t g d t s
d t b e s c t e
(8)
Noticing that i
p pb b e it follows that the
information relative to the phase degree of freedom is
connected only to the coefficient 1 s . If the quantum
emitter is in its ―g‖ state then light is connected to the first
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
113
probe puse. If the quantum emitter is in the ―e‖ level than
the light is connected to the second probe pulse. In other
terms, monitoring the state of the quantum emitter we
acquire the which-way information about the origin of the
photon and, therefore, due to fundamental quantum
complementarity principle, interference disappears. On
the contrary, if the second control pulse is not sent than it
is not possible to get such information and, therefore,
interference manifests itsself.
Conclusions
The presented researches explains the reason why
sudden death and sudden ribirth of coherence happen
highlighting that the information relative to a coherence
can be transferred to other internal degrees of freedoms of
the considered physical system. Such achivement is
connected to the possibility to experimentally control in
an ultrafast way the trasfer of information within a certain
physical system thus paving the way to technological
quantum information advancements.
At the meanwhile, these studies explain the way to
ultrafast ontrol wave-particle duality thanks to a
homodyne-like detection scheme. The studied scheme
could find easy experimental realization thanks to its
simplicity.
References [1] A. Ridolfo, R. Vilardi, O. Di Stefano, S. Portolan, and S. Savasta,
Phys. Rev. Lett. 106, 013601 (2011); [2] J. M. Raimond, M. Brune, S. Haroche, Rev. Mod. Phys. 73, 565
(2001);
[3] C. Monroe, Nature (London) 416, 238 (2002); [4] L. M. Duan and H. J. Kimble, Phys. Rev. Lett. 92, 127902 (2004);
[5] C. Weisbuch, M. Nishioka, A. Ishikawa, and Y. Arakawa, Phys.
Rev. Lett. 69, 3314 (1992); [6] J. P. Reithmaier, G. Sek, A. Löffler, C. Hofmann, S. Kuhn, S.
Reitzenstein, L. V. Keldysh, V. D. Kulakovskii, T. L. Reinecke,
and A. Forchel, Nature (London) 432, 197 (2004); [7] T. Yoshie , A. Scherer, J. Hendrickson, G. Khitrova, H. M. Gibbs,
G. Rupper, C. Ell, O. B. Shchekin, and D. G. Deppe, Nature
(London) 432, 200 (2004); [8] K. Hennessy, A. Badolato, M. Winger, D. Gerace, M. Atatüre, S.
Gulde, S. Fält, E. L. Hu, and A. Imamoglu, Nature 445, 896
(2007); [9] I. Chiorescu, P. Bertet, K. Semba, Y. Nakamura, C. J. P. M.
Harmans, and J. E. Mooij, Nature (London) 431, 159 (2004);
[10] A. A. Abdumalikov, O. Astafiev, A. M. Zagoskin, Yu. A. Pashkin, Y. Nakamura, and J. S. Tsai, Phys. Rev. Lett. 104, 193601 (2010);
[11] B. Peropadre, P. Forn-Diaz, E. Solano, and J. J. Garcia-Ripoll,
Phys. Rev. Lett. 105, 023601 (2010); [12] J. McKeever, A. Boca, A. D. Boozer, J. R. Buck, and H. J. Kimble,
Nature 425, 268, (2003);
[13] A. Dousse, Jan Suffczyński, , A. Beveratos, O. Krebs, A. Lemaître, I. Sagnes, J. Bloch, P. Voisin and P. Senellart, Nature (London)
466, 217, (2010);
[14] O. Di Stefano, A. Ridolfo, S. Portolan, and S. Savasta, Opt. Lett. 36 No.22, (2011);
[15] R Vilardi, A. Ridolfo, S. Portolan, S. Savasta, O. Di Stefano,
Quantum Complementarity of Cavity Photons Coupled to a Three-Level System, to be published by Physical Review A.;
[16] O. Di Stefano, R. Stassi, A. Ridolfo, S. Patanè, and S. Savasta,
Phys. Rev. B, 84, 085324 (2011).
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SEMINARI (Invited)
DEL DOTTORATO DI RICERCA
IN FISICA
Effettuati nel 2011
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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 19 Gennaio 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica
V.le F. Stagno d‘Alcontes 31, Messina
Prof. Józef SURA Heavy Ion Laboratory (HIL), University of Warsaw, Poland
Seminar title:
The HIL Cyclotron and associated ion optics
Abstract The isochronous cyclotron of the Heavy Ion Laboratory of Warsaw accelerates ions with mass to charge
ratio in the range of A/Q=(2-6) and energies up to 30 MeV per nucleon.
The design of this setup includes many of the accelerator physics and ion optics elements.
These elements beginning with the ECR ion source, injection, acceleration, extraction, beam lines, till
the experimental setups will be discussed.
________
Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 7 Febbraio 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica
V.le F. Stagno d‘Alcontes 31, Messina
Dr. Ernesto Amato Dipartimento di Scienze Radiologiche,
Policlinico dell‘Università di Messina
Seminar title:
The Geant4 Monte Carlo package from Cern and its applications to nuclear, particle,
astroparticle and medical radiation physics
Abstract Geant4 (Geometry and Tracking 4) is a Monte Carlo toolkit developed by Cern in object-oriented C++
programming paradigm, for the simulation of nuclear and particle interaction.
It offers a wide set of complementary physics models, based either on theory or on experimental data
and parametrizations, for electromagnetic and hadronic interactions in energy ranges spanning from
some tens of eV to TeV, together with models for nuclear excitation, fission and decay. Extensions to
low energy interactions and also to optical photon propagation are available.
Complex geometries can be defined and managed, made from elements or compounds whose properties
can be obtained from databases or user defined. Volumes can be made ―sensitive‖ to simulate detectors,
through the use of hits and digitisation classes.
Primary particles propagate through the defined geometry according to the tracking and stepping rules,
obeying to the physics models adopted and to the selected cuts.
Interaction tracks and cascades can be visualized either online or offline, and relevant quantities are
scored in 1-2-3D histograms and n-tuples. Several ancillary softwares from Cern and from application
developer teams aid the user in the I/O phases.
After a general introduction to the Geant4 concept, architecture and physical models, I will comment
on the different fields of application, spanning from the high energy physics and astrophysics
experiments, to the application of radiation physics for dosimetry and radioprotection from sources of
photons, leptons and hadrons.
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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina
22 Febbraio 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica,
V.le F. Stagno d‘Alcontres 31, S. Agata, Messina
Prof. C.A. Squeri, Prof. V. Candela, Dott. J. Trombetta, Dott. A. M. Roszkowska Ophthalmology Unit, Department of Surgical Specialties, University Hospital of Messina,
Messina, Italy.
Seminar title: “Clinical applications of the different laser platforms in ophthalmology”
Abstract: The purpose of this seminary is to present the clinical applications of the different lasers in
ophthalmology. The following lasers will be presented:
Femtosecond lasers. This kind of lasers is characterized by ultrashort pulses. They perform horizontal or vertical corneal cuts
and are used in corneal and refractive surgery. They are adopted in corneal lamellar keratoplasty and in
refractive surgery.
Excimer laser and solid state laser. The characteristics of these lasers are used to modify the anterior corneal shape. Flattening or
steppening of the corneal surface permit to correct existing refractive errors, so such lasers are widely
used in corneal refractive surgery.
Argon laser and diode laser These lasers perform retinal photocoagulation. They create retinal scars with effect on retinal
pathologies such as diabetic retinopathy, retinal ruptures or holes and degenerations.
NdYAG laser. It is above all a disruptive laser used to treat secondary cataract performing posterior capsulotomy. It
is also adopted to resolve an angle closure glaucoma by localized iridotomy (puncture-like openings
through the iris without the removal of iris tissue). ________
Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 4 Marzo 2011, ore 10.00, Conference Room CNR-IPCF
V.le F. Stagno d‘Alcontres 37, S. Agata, Messina
Seminar title: Ettore Majorana and the Birth of Autoionization
Ennio Arimondo
Dipartimento di Fisica “E. Fermi”, Università di Pisa
Abstract: In some of the first applications of modern quantum mechanics to the spectroscopy of
many-electron atoms, Ettore Majorana in 1931 solved several outstanding problems by developing
the theory of autoionization. Later literature makes only sporadic references to this accomplishment.
After reviewing his work in its contemporary context, we describe subsequent developments in
understanding the spectra treated by Majorana, and extensions of his theory to other areas of
physics. We find several puzzles concerning the treatment of Majorana's work in the subsequent
literature and the way in which the modern theory of autoionization was developed.
The relevant papers are those numbered 3 and 5 in the convenient collection, Ettore Majorana
Scientific Papers: On the occasion of the centenary of his birth, ed. G. F. Bassani et al. (SIF,
Bologna 2006), where they are accompanied by English translations and commentary. The originals
are, respectively, ``I presunti termini anomali dell'elio,"E. Majorana, Il Nuovo Cimento, 8, 78 (1931)
and ``Teoria dei tripletti P' incompleti," E. Majorana, Il Nuovo Cimento, 8, 107 (1931).
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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 24 marzo, alle ore 15.00 nella sala conferenze del CNR di Messina
V.le F. Stagno d‘Alcontres 37, S. Agata, Messina
Seminar Title: Optical Properties of Carbon-based Materials
Elefterios Lidorikis Department of Materials Science & Engineering, University of Ioannina, Ioannina GR-45110 Greece
Abstract: Carbon nanotubes (CNTs), and more recently graphene, have been at the center of
nanotechology research, with the search for new technologies based on their mechanical and
electrical properties ever increasing. Graphene, a two-dimensional honeycomb lattice of carbon
atoms, can be thought of as the ―building block‖ of other carbon allotropes: it can be ―wrapped‖
into fullerenes, ―rolled‖ into CNTs or ―stacked up‖ into graphite, with many of their properties
deriving from graphene.
In this presentation we discuss different aspects of the photonic response of graphene and CNTs.
After a brief introduction to the basic electronic structure and optical properties of graphene, we
discuss recent advances in understanding interference-enhanced (IERS) and surface-enhanced
Raman scattering (SERS) phenomena in graphene. Especially in terms of SERS, graphene provides
the ideal prototype two-dimensional test-material for its investigation. We discuss recent SERS
experiments on graphene and develop a quantitative analytical and numerical theory for its
description.
Next, we investigate the photonic properties of two-dimensional CNT arrays for photon energies up
to 40eV and unveil the physics of two distinct applications: deep-UV photonic crystals and total
visible absorbers. We find three main regimes: for small intertube spacing of 20-30nm, we obtain
strong Bragg scattering and photonic band gaps in the deep-UV range of 25~35 eV. For
intermediate spacing of 40-100nm, the photonic bands anti-cross with the graphite plasmon bands
resulting into a complex photonic structure, and a generally reduced Bragg scattering. For large
spacing >150nm, the Bragg gap moves into the visible and decreases due to absorption. This leads
to nanotube arrays behaving as total optical absorbers. These results can guide the design of CNT-
based photonic applications in the visible and deep UV ranges.
________ Dottorato di Ricerca in Fisica, Università di Messina
Avviso di Seminario 30 Marzo 2010, Ore 15.00, aula E. Majorana, Dipartimento di Fisica, Università di
Messina, V.le F. Stagno D‘Alcontres 31, S. Agata, Messina
Prof. Avazbek NASIROV Bogoliubov Laboratory of Theoretical Physics of the Joint Institute for Nuclear Research of Dubna
(Russia)
Seminar title: "The role of the entrance channel in study of fusion-fission reaction mechanisms "
Abstract: Evaporation residues and binary fragments are main products of the heavy ion collisions at
beam energies around the Coulomb barrier.
The new superheavy elements Z=110-118 are the evaporation residues after emission of neutrons from
the heated compound nucleus which is formed in the complete fusion of projectile and target nuclei.
Due to very small cross section of the synthesis of superheavy elements it is convenient to study the
reaction mechanism by the analysis of fusion-fission fragments formed at fission of compound nucleus.
But the fusion-fission fragments are mixed with the quasifission and fast fission fragments which are
formed without formation of compound nucleus. In this seminar we will discuss the mechanisms and
contributions of these three fissionlike processes to help experimentalists at the choice of reactions for
the synthesis of new superheavy elements.
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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 14 Aprile 2011, ore 15.00, Aula E. Majorana, Dipartimento di Fisica
V.le F. Stagno d‘Alcontres 31, S. Agata, Messina
Seminar title:
Nuclear Energy: how does it work?
Dr.ssa Marina Trimarchi
Dipartimento di Fisica, Università di Messina
Abstract: The possibility to produce energy from nuclear transmutations is a consequence of the
Einstein‘s equation, stating the equivalence between mass and energy.
Fission reactions represent a very powerful energy source, showing a yield 2 millions higher than
that of fossil fuels, without greenhouse gases emission.
Nuclear power plants working principles will be illustrated, with particular attention to safety
aspects, in operational mode as well as in case of accident. In particular, differences between
various generations reactors will be stressed, starting from old RMBK type (Chernobyl) to the
newest EPR type. Other correlated aspects, as nuclear waste disposal and non-proliferation of
nuclear weapons will be considered.
Finally, due to recent event regarding Fukushima nuclear accident, an overview of the actual
nuclear risk and its consequences worldwide will be given. ________
Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina
5 Maggio 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica,
V.le F. Stagno d‘Alcontres 31, S. Agata, Messina
Dr.ssa Valentina Venuti Dipartimento di Fisica, Universita’ di Messina, CNISM, UdR Messina, Viale Ferdinando Stagno
D’Alcontres 31, P.O. BOX 55, 98166 Messina, ITALY. Email: vvenuti@unime.it
Seminar title:
Vibrational dynamics and chiral recognition in Ibuprofen/ -cyclodextrins inclusion complexes:
FTIR-ATR and numerical simulation results
Abstract Cyclodextrins are supramolecular host systems able to encapsulate molecules in their hydrophobic
cavity via noncovalent interactions. Their chiral recognition properties, not fully characterized yet, are
of great relevance in pharmaceutical industry.
Here, we studied how the vibrational properties are affected by the chiral recognition process, upon
selection of the non-steroidal anti-inflammatory drug Ibuprofen (IBP) in its chiral (R)- and (S)-, and
racemic (R, S)- forms, as model guest, and native and modified -cyclodextrins ( -CDs) as model host.
The changes induced, as a consequence of complexation, on the vibrational spectrum of IBP, have been
studied, in solid phase, by attenuated total reflection Fourier transform infrared FTIR-ATR. The
recorded spectra have been compared with the wavenumbers and IR intensities as obtained by
simulation for the free and complexed guest molecule. By the temperature-dependent analysis of the
vibrational spectra in the C=O stretching region, the complexation mechanism has been discussed. It
turned out to be enthalpy-driven, with enantiomers of IBP giving rise to more stable inclusion
complexes with respect to the racemate. This combined experimental-numerical approach gave crucial
information on the expected different ―host-guest‖ interactions that drive the chiral recognition process,
helpful to put into evidence differences in the conformational properties of the complexes, that are
retained a prerequisite for chiral recognition.
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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 14 Giugno 2011, ore 12.00, Aula E. Majorana, Dip.to di Fisica,
V.le F. Stagno d‘Alcontres 31, S. Agata, Messina
Dr.ssa Mariapompea Cutroneo Dottorato di Ricerca in Fisica, Università di Messina
Seminar title:
“High Energy proton/ion beams production by sub-ns, kJ-laser plasma interaction”
Abstract The purpose of this seminar is to present some preliminary results recently obtained in the European &
International Experiment, directed by Prof. L. Torrisi of Messina University, at the PALS Laboratory of
Prague (Czech Republic), under the support given by LASERLAB Europe.
Particularly will be presented some preliminary results concerning the plasma generation in forward
direction through thin laser irradiated targets, the plasma laser acceleration of protons and ions at
energies above 1 MeV, the new detection technique employing Thomson parabola and semiconductor
SiC detectors in time-of-flight configuration, and the first measurements of D-D nuclear fusion induced
by 4 MeV deutons accelerated by the laser-plasma.
The original results and experimental approaches will be discussed in view of a more details
descriptions that will be given in the specific scientific Journals.
________
Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 21 Giugno 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica,
V.le F. Stagno d‘Alcontres 31, S. Agata, Messina
Seminar title: Electron correlations in metals: Dynamical mean-field theory
Václav Janiš Institute of Physics, Academy of Sciences of the Czech Republic,Prague
Abstract Electrons in metals feel only a screened, short-range Coulomb repulsion. In most of the transition
metals, lanthanides and actinides electron correlations are not negligible. To describe the correlation
effects correctly one needs a reliable description of strong electron correlations. Gross features of weak
excitations of the ground state of interacting fermions are described by Fermi-liquid theory. To assess
collective phenomena with quantum coherence in heavy metals, it is necessary to go beyond the
framework of Fermi liquid. The way to go systematically beyond Fermi-liquid theory is offered by the
so-called Dynamical Mean-Field Theory. We review in this talk the underlying ideas of the dynamical
mean-field theory originating in the single-impurity Anderson model and the Kondo effect. We further
discuss various aspects of presently the most advanced theory of strongly correlated electrons with
examples of its application in model and realistic calculations of electronic properties of metals.
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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 23 Giugno 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica,
V.le F. Stagno d‘Alcontres 31, S. Agata, Messina
Seminar title: Electrical conductivity and charge diffusion in disordered solids
Václav Janiš Institute of Physics, Academy of Sciences of the Czech Republic,Prague
Abstract: Electrical resistivity (Ohm‘s law) in solids is caused by the scattering of almost free conduction
electrons on impurities and irregularities in the periodic lattice. The basic theoretical tools for
description of quantum transport are linear response theory and Kubo formulas. We review in this talk
many-body and Green function methods of calculation of the impact of scatterings of electrons on
randomly distributed impurities in metals. We stress the necessity of renormalizations of the
perturbation expansion in the strength of the impurity potential and of consistency between one- and
two-electron Green functions dictated by conservation laws, electron-hole symmetry and and gauge
invariance of the electromagnetic system. Finally we discuss disorder-driven metal-insulator transitions
due to discharging of the Fermi energy and due to vanishing of diffusion in the limit of strong
randomness.
_______
Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 28 Giugno 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica,
V.le F. Stagno d‘Alcontres 31, S. Agata, Messina
Seminar title:
Il contributo Light-by-Light al momento magnetico anomalo del muone.
Stato attuale e prospettive future.
D. Moricciani INFN, Sezione di Roma \Tor Vergata", I-00133 Roma, Italy
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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 7 Luglio 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica,
V.le F. Stagno d‘Alcontres 31, S. Agata, Messina
Seminar title:
MESON PHOTOPRODUCTION AT GRAAL AND MAMBO
Dott.ssa R. Di Salvo
INFN Sezione di Roma Tor Vergata
Abstract Meson photoproduction on the nucleon is a powerful tool for the understanding of the nucleon
structure and of the baryon resonances involved in the reaction process. Polarized photon beams, in
combination with large solid angle apparata and/or high precision spectrometers, allow to access
polarization observables, which are particularly sensitive to the properties of baryon resonances, such as
parity and spin. Some of the main results of the GRAAL experiment in Grenoble and the future plans
for the MAMBO experiment, which is presently under construction in Bonn, will be shown and
discussed in detail.
________
Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 11 Luglio 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica,
V.le F. Stagno d‘Alcontres 31, S. Agata, Messina
Seminar title:
Thomson parabola spectrograph in investigations of MeV energy ions from laser plasma ion
sources
Andriy Velyhan Institute of Physics, ASCR, Na Slovance 2, 182 21 Prague 8, Czech Republic
Abstract
Laser ion sources (LIS) already have found a wide applications in areas such as material modification,
ion implantation, pulsed laser deposition. LIS can deliver ions with ionization states from Z= 1 up to 55,
and energies ranges from hundreds of eV up to several MeV. Investigations of the interaction of laser
radiation with solid targets is possible by using of Thomson parabola spectrograph (TPS). The operation
principle of the TPS is based on the gradual passage of ions through parallel electric and magnetic
fields. It is an excellent device, which is capable to give a general overview of the charge states and of
the velocity (kinetic energy) distributions of all type of ions produced in a single laser shot only.
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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 28 Settembre 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica, V.le F. S. d‘Alcontres 31, S. Agata,
Messina; Seminar title: “Laser-generated plasma and its applications”; Dr. Francesco Caridi,
Physics Ph.D. ; Facoltà di Scienze MM. FF. NN., Univ. di Messina, Viale F. S. d’Alcontres, 31 – 98166
– Messina, Italy ;INFN-Sez. CT, Gr. Coll. di Messina, Viale F. S. d’Alcontres, 31 – 98166 – Messina
Plasma production by laser ablation (PLA) of solid targets in vacuum is a topic of growing interest for
many applications in different fields, such as diagnostics techniques, ion acceleration, nuclear physics,
material processing and cultural heritage. Key plasma parameters, such as equivalent temperature,
density, acceleration voltage, ion charge state and fractional ionization, are evaluated using appropriate
diagnostics instruments, such as ion collector, ion energy analyzer, mass quadrupole spectrometer,
optical spectroscope. These tools give us essential information to understand the mechanism of non-
equilibrium plasma development and kinetics. A special interest of PLA concerns the ion acceleration
with high-electrical fields generated in sub-millimeter space by hot and dense laser-generated non
equilibrium plasmas. This new method of producing ion beams is more appealing than classical
techniques that use large accelerator facilities, and, recently, it has been investigated in order to develop
a new generation of laser ion sources (LIS). Furthermore, when extremely intense laser beams interact
with deuterated targets, D-D nuclear fusion reactions can be achieved in hot and dense plasmas. Many
laboratories are using PLA in order to grow thin films as coverage of different substrates. The film
properties, such as stoichiometry, roughness, grain size, crystallinity and porosity, can be modified on
the basis of the used laser wavelength, pulse intensity, pulse width, substrate nature, irradiation
environment conditions, etc. The technique is useful in many scientific fields, such as microelectronics,
chemistry, biomedicine and metallurgy. Laser Ablation coupled to Mass Quadrupole Spectrometry
(LAMQS) is a new technology recently developed for the depth profile and compositional analysis of
different solid materials placed in vacuum. It is very helpful in the field of cultural heritage in order to
compare their composition and morphology and to identify their origin and the type of manufacture. ________
Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 18 Ottobre 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica, V.le F. S. d‘Alcontres 31, S. Agata,
Messina; Seminar title: Electroencephalographic signal processing: the use of Independent
Component Analysis and its application to complex motor task. Dr.ssa Simona Lanzafame University of Messina, Department of Matter Physics and Electronic Engineering.
The City College of New York, CUNY, Sophie Davis School of Medicine.
Electroencephalographic (EEG) signal obtained from scalp electrodes is a sum of the large number of
neurons potentials. The interest of the scientific community is in studying the potentials in the sources
inside the brain and not only the potentials on the scalp, which globally describe the brain activity.
The recovery of the exact cortical distribution of an EEG source region is limited by the unsolved of the
inverse source localization problem. For example, far-field potentials from two synchronously active but
physically opposing cortical source areas – e.g., source areas facing each other on opposite sides of a
cortical sulcus – may cancel and their joint activity will have no effect on the scalp data. An ideal goal
for EEG analysis should be to detect and separate activities in multiple concurrently active EEG source
areas, regardless of their relative straights at different moments. A new approach to finding EEG source
activities has been developed based in a simple physiological assumption that across sufficient time, the
EEG signals arising in different cortical source domains are temporally independent of each other. This
means that measuring the scalp EEG activity produced in some of the source domains at a given
moment allows no inferences about EEG activities in the other source domains at the same instant. This
insight and the resulting algorithms for signal separation that have emerged in the last decade have
created a new field within signal processing in general, known in particular as independent component
analysis (ICA). We will discuss the important findings obtained by a novel application of the ICA
algorithm to complex motor task.
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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 14 Novembre 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica, V.le F. S. d‘Alcontres 31, S. Agata,
Messina; Seminar title: Fukushima: Eight months after ; Dr.ssa Marina Trimarchi
Dipartimento di Fisica, Università di Messina e INFN – Gruppo Collegato di Messina
Abstract The accident occurred at the Fukushima Daichi NPP as a consequence of the Japan Earthquake and
Tsunami, classified at 6th level of the INES, has involved a significant release of radioactive materials,
inducing a considerable contamination and irradiation risk to people and environment.
Actually the short term consequences typical of a nuclear accident can be considered quite overcome,
although the recovery process of the reactors of Fukushima Daichi NPP is a slow and difficult process,
still requiring continuous and arduous efforts from TEPCO workers and Japanese volunteers.
For what concerns the long term risks due to this nuclear accident, a comprehensive understanding of
the contamination status of the environment is necessary to choose the suitable countermeasures to
adopt. In this framework, Japanese government is still providing an astonishing effort in evaluating
contamination and exposure data, that are continuously and correctly shared not only with the scientific
and government institutions involved, but also with the public. A survey of the reactor status, and of the
actual contamination and exposure levels will be provided, together with a description of the
remediation activities and countermeasures adopted from the government institution, in the framework
of the international recommendations. Finally, the lesson learned from the Fukushima accident will be
discussed, and a short comparison with the Chernobyl experience will be attempted, to better understand
risks and consequences of a nuclear accident in the third millennium scenario. ________
Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 21 Novembre 2011, ore 15.00, Sala Seminari IPCF-CNR, V.le F. S. d‘Alcontres 37, S. Agata, Messina
Seminar title: Salty ice under pressure; Dr. Antonio Marco Saitta
Physique des Milieux Denses, IMPMC, CNRS-UMR 7590, Université Pierre et Marie Curie, Paris
Abstract Water, wherever it exists in nature, contains unavoidably significant amounts of dissolved ionic species.
Nonetheless, surprisingly little experimental attention has been paid on the high pressure behaviour of ―salt
water‖ compared to pure water. In a recent study combining neutron diffraction and molecular dynamics
simulations we showed the existence [3] of a polyamorphic transition in LiCl:6D2O between a high-density
(HDA) and a very-high-density amorphous (VHDA) form. In spite of the high amount of salt, LiCl:6D2O
vitrifies at ambient pressure in a structurally compact form very similar to the relaxed high-density
amorphous phase of pure water (e-HDA) [1]. We show that the transition to salty-VHDA takes place abruptly
at 120 K and 2 GPa under annealing at high pressure, is reversible. We suggest that the transition is linked to
a local structural reorganization of water molecules around the Li ions. The possible connection of this
transition with the analogous observed [1] in pure water and the generality of the occurrence of a
polyamorphism phenomenon in solutions in which one component, water, can have two critical points [2]
will be discussed. Under further annealing at high pressure (~4GPa), the salty-VHDA amorphous crystallizes,
for a temperature of ~270 K, in a new and unexpectedly simple salt hydrate [4], which can be regarded as an
―alloyed‖ high-pressure ice phase. Such ―salty‖ ice VII has significantly different structural properties
compared to pure ice VII, such as a 8% larger unit cell volume, 5 times larger displacement factors, frozen
rotational disorder, absence of transition to an ordered ice VIII structure, and most likely ionic conductivity.
Our study strongly suggests that there is a whole new class of salt hydrates based on various kinds of solutes
and high pressure ice forms. If these exist in nature in significant quantity, their physical properties would be
highly relevant for the understanding of icy bodies in the solar system.
[1] R. J. Nelmes et al., Nature Phys. 2 414, (2006).
[2] P. G. Debenedetti and H. E. Stanley, Phys. Today 40 (2003).
[3] L. E. Bove, S. Klotz, J. Philippe, and A. M. Saitta, Phys. Rev. Lett. 106, 125701 (2011).
[4] S. Klotz, L. E. Bove, T. Strassle, T. C. Hansen, and A. M. Saitta, Nature Materials 8, 405 (2009)
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Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 1 Dicembre 2011, ore 15.00, Sala Seminari IPCF-CNR
V.le F. Stagno d‘Alcontres 37, S. Agata, Messina
Seminar title:
A novel hybrid top-down/bottom-up approach for nanoparticle synthesis:
Laser ablation in reversed micellar solution
Dr. Pietro Calandra IPCF-CNR Sede di Messina
If the building up of smaller and smaller structures promptly answers the recent technological request of
more and more miniaturized devices, it is also true that new and exotic features arise below a certain
size threshold of particles basically due to quantum confinement of charge carriers (Quantum Size
effects). In addition to size effects, further peculiar properties are expected to arise by controlling the
spatial location of different materials, e.g. semiconductor and metal domains, within each nanoparticle
[1]. In fact, it is well known that semiconductor/metal junctions give rise to very interesting phenomena
which have been exploited in a wide range of technological applications (transistors, rectificator
junctions, Ohmic contacts as well as effective photocatalysts).
In order to prepare A@B-type materials (A and B referring to two different materials), we set up a novel
synthetic method based on the laser ablation of a target of the material A, immersed in a reversed
micellar solution containing nanoparticles of the material B. This strategy is a winning example of an
hybrid approach combining, in a synergistic way, the advantages of a top-down approach (high purity of
the ablated particles [2]) and a bottom-up one (synthesis of B and self-assembly of A onto it).
[1] T. Hirakawa and P. V. Kamat, J. Am. Chem. Soc. 127, 3928 (2005).
[2] P. Calandra et al., Materials Letters 64, 576 (2010).
________
Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 5 Dicembre 2011, ore 15.00, Sala Seminari IPCF-CNR
V.le F. Stagno d‘Alcontres 37, S. Agata, Messina
Seminar title:
Magnetically induced birefringence in magnetic nanoparticles suspensions
Dr. Mikolaj Pochylski Division of Optics, Dept. of Physics, Adam Mickiewicz University, Poland
Abstract In this talk the magnetically induced birefringence method will be shown as a method useful in
discrimination between different mineral structures and sizes of magnetic nanoparticles. The basic
principles of the technique and its simple experimental realization will be explained. The applicability of
the method will be presented for several biomedically relevant systems.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
126
Dottorato di Ricerca in Fisica dell’Università degli Studi di Messina 20 Dicembre 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica,
V.le F. Stagno d‘Alcontres 31, S. Agata, Messina
Seminar title:
La «particella di Dio» e l'origine della massa
Paolo Castorina Dipartimento di Fisica e Astronomia, Universita di Catania
Abstract
Al Centro Europeo Ricerche Nucleari (CERN) di Ginevra è in funzione la piùgrande macchina che
l'uomo abbia mai costruito: il Large Hadron Collider (LHC). Si accelerano e si fanno urtare particelle di
energia altissima perverificare le leggi fondamentali della Natura.
LHC ci ha già permesso di raggiungere temperature molto simili a quelle dell'inizio del Big Bang
cosmologico ed al CERN è stata anche intrappolata l'antimateria. Ma non siè ancora trovata la particella
di Higgs la cui esistenza confermerebbe completamente l'attuale teoria unificata delle interazioni
elettromagnetiche e deboli e, soprattutto, spiegherebbe l'origine della massa. La massa, anche quella
delle particelle più piccole, non è una proprietà fondamentale. Essa deriva dalle forze di interazione e, in
particolare, dall'esistenza di una nuova particella, battezzata "particella di Dio", attraverso un
affascinante meccanismo, detto rottura spontanea della simmetria, che viene descritto con semplici
esempi.
Infine, i recenti risultati preliminari di LHC, presentati al CERN il 12 Dicembre 2011 e riportati dalla
stampa internazionale, verranno brevemente discussi.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
127
Organizzazione
del
Dottorato di Ricerca in Fisica dell‘Università di Messina
Ciclo (XXVI)
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
128
Organization and Personnel
PhD COORDINATOR : PROF. LORENZO TORRISI
TEACHERS OF REFEREMENT
FOR THE DIFFERENT CURRICULA:
PROF. G. CARINI CURRICULUM STRUTTURA DELLA MATERIA
PROF. GIORGIO GIARDINA CURRICULUM FISICA NUCLEARE
PROF. PAOLO V. GIAQUINTA CURRICULUM FISICA MAT. SOFF.
E DEI SIST. COMPL.
PROF. DOMENICO MAJOLINO CURRICULUM FISICA APPLICATA
DIRECTOR OF PHYSICS DEPARTMENT OF MESSINA
UNIVERSITY:
PROF. GIACOMO MAISANO
DIRECTOR OF MATTER PHYSICS AND ELECTRONIC
ENGINEERING DEPARTMENT:
PROF. FORTUNATO NERI
SCHOOL MANAGER: DR PAOLA DONATO
ADMINISTRATION PERSONNEL: Mrs. GIUSEPPA LA SPADA
Mrs. ROSANNA ARENA
Mrs. GAETANA PANTO’
Mr. SALVATORE RANDO
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
129
Curriculum di Struttura della Materia
(15 moduli/180 ore).
DISCIPLINA MODULI Prof.copertura
Fisica stati
condensati (45)
Fisica dello stato solido (15) Ginatempo
Fisica dei solidi amorfi (15) D‘Angelo
Fisica dei liquidi (15) Caccamo
Fisica Teorica (20) Fisica Relativistica (10) Savasta
Teoria dello scattering
elettromagnetico (10) Borghese
Metodi Matematici
e computazionali
della Fisica (30)
Tecniche di Calcolo della
Fisica (10) Savasta
Fondamenti di informatica e
Fisica computaz. (10) Costa-
Ginatempo
Simulazione di sistemi
all‘equilibrio (10) Costa-F.Sajia
Tecniche
Spettroscopiche
(40)
Spettr. Neutronica (10) Wanderlingh
Spettr. Ottica (10) Majolino
Spettr. Acustica e dielettrica
(10) Mandanici-
Tripodo
Spettr. Elettronica (10) Mondio
Fisica Sistemi
Complessi (30)
Fenomenologia dei sistemi
complessi (15) Magazù
Fisica sistemi a molti corpi
(15) Malescio-
Prestipino
Fisica Nucleare
(15) Teoria delle interazioni
fondamentali (15) Trifirò
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
130
Curriculum di Fisica della Materia Soffice e dei Sistemi complessi
(15 moduli/180 ore).
DISCIPLINA MODULI
Prof.copertura
Fisica degli stati
condensati (45)
Fisica dei liquidi (15) Caccamo
Fisica dei solidi amorfi (15) D‘Angelo
Sistemi metastabili (15) Giaquinta
Fisica della Materia
soffice e dei sistemi
complessi (45)
Colloidi e polimeri e aggregati
supramolecolari (20)
Micali
Sistemi di interesse biofisico (15) Magazù
Sistemi caotici, finanziari; reti (10) Malescio
Argomenti avanzati di
Fisica dei Liquidi (20)
Miscele di liquidi e liquidi carichi
(10)
F. Saija
Liquidi a legame idrogeno (10) Mallamace
Tecniche
Spettroscopiche (30)
Spettr. Neutronica (10) Wanderlingh
Spettr. Ottica (10) Majolino
Spettr. Acustica e dielettrica (10) Mandanici-
Tripodo
Metodi Matematici e
computazionali della
Fisica (20)
Fondamenti di informatica e Fisica
computazionale (10)
Costa-
Ginatempo
Simulazione di sistemi
all‘equilibrio (10)
Costa-F.Saija
Metodi di
Simulazione Avanzati
(20)
Simulazione di sistemi fuori
dall‘equilibrio (10)
Prestipino
Metodi numerici per lo studio di
transizioni di fase (10)
Prestipino
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
131
Curriculum di Fisica Applicata ai Beni Culturali
(15 moduli/180 ore).
DISCIPLINA MODULI Prof. copertura
Fisica stati condensati
(25)
Fisica dei solidi amorfi (15) D‘Angelo
Fisica dei Materiali (10) Mondio
Fisica Teorica (10) Teoria dello scattering
elettromagnetico (10)
Borghese-Iatì
Metodi Matematici e
computazionali della
Fisica (20)
Tecniche di Calcolo della Fisica
(10)
Savasta
Fondamenti di informatica e
Fisica computaz. (10)
Costa-Ginatempo
Tecniche
Spettroscopiche (50)
Introduzione alle tecniche
spettroscopiche (10)
Crupi
Spettr. Neutronica (10) Wanderlingh
Spettr. Ottica (10) Majolino
Spettroscopia Acustica e
dielettrica (10)
Mandanici-
Tripodo
Spettr. Elettronica (10) Mondio
Fisica dei sistemi
complessi (30)
Fenomenologia Sistemi complessi
(15)
Magazù
Fisica sistemi a molti corpi (15) Malescio-
Prestipino
Metodologie Fisiche
applicate ai Beni
Culturali (45)
Archeometria (10) Majolino
Metodologie Sperimentali e
strumentazione in Fisica applicata
ai Beni Culturali (15)
Torrisi-Magazù
Metodologie nucleari in Fisica
Applicata (20)
Barnà-Trifirò-
Fazio
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
132
Curriculum di Fisica Applicata ai Beni Ambientali
(15 moduli/180 ore).
DISCIPLINA MODULI Prof. copertura
Fisica stati condensati
(30)
Fisica dello stato solido (15) Ginatempo
Fisica dei solidi amorfi (15) D‘Angelo
Fisica Teorica (10) Teoria dello scattering
elettromagnetico (10)
Borghese-Iatì
Metodi Matematici e
computazionali della
Fisica (20)
Tecniche di Calcolo della Fisica
(10)
Savasta
Fondamenti di informatica e Fisica
computaz. (10)
Costa-Ginatempo
Tecniche
Spettroscopiche (40)
Introduzione alle tecniche
spettroscopiche (10)
Crupi
Spettr. Neutronica (10) Wanderlingh
Spettr. Ottica (10) Majolino
Radioattività e Spettroscopia
Gamma (10)
Barnà - Trifirò
Fisica dei sistemi
complessi (30)
Fenomenologia Sistemi complessi
(15)
Magazù
Fisica sistemi a molti corpi (15) Malescio-
Prestipino
Metodologie Fisiche
applicate ai Beni
Ambientali (50)
Metodologie Sperimentali e
strumentazione in Fisica applicata
ai Beni Ambientali (15)
Torrisi-Magazù
Inquinamento Acustico e normativa
(15)
Federico
Metodologie nucleari in Fisica
Applicata (20)
Barnà-Trifirò-
Fazio
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
133
Curriculum di Fisica Nucleare
(13 moduli/180 ore).
DISCIPLINA MODULI Prof. copertura
Fisica Teorica (10)
Teoria dello scattering elettromagn.
in processi Nucleari (10)
Iatì-Maidaniuk-
Giardina
Fisica Nucleare
(65)
Teoria delle interaz. Fondam. (15) Trifirò
Teoria delle reazioni Nucleari
indotte da ioni leggeri (10)
Giardina -
Nasirov
Teoria delle reazioni Nucleari
indotte da ioni pesanti (20)
Giardina -
Nasirov
Spettroscopia Nucleare (20) Barnà
Metodi Matematici
e computazionali
della Fisica (15)
Acquisizione ed elaborazione dei
dati sperimentali (15)
Barnà
Fisica Sistemi
Complessi (30)
Fenomenologia sistemi complessi
(15)
Magazù
Fisica dei sistemi a molti corpi (15) Malescio-
Prestipino
Apparati di
rivelazione in
Fisica Nucleare e
subnucleare (30)
Rivelazione dei prodotti di
reazione e metodologie di Analisi in
Fisica Nucleare (15)
Trifirò
Rivelazione dei prodotti di
reazione e metodologie di Analisi in
Fisica subnucleare (15)
Trifirò
Fisica subnucleare
(30)
Risonanze barioniche con sonde
elettromagnetiche in fisica
relativistica (10)
Di Salvo
Procedure di simulazione nelle
reazioni di fotoproduzione di
Mesoni (10)
Moricciani
Astrofisica Nucleare (10) Italiano
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
134
Collegio dei Docenti del
Dottorato di Ricerca in Fisica
Ciclo XXVI
1. Abramo Maria Concetta
2. Barnà Calogero Renato
3. Borghese Ferdinando
4. Branca Caterina
5. Caccamo Carlo
6. Carini Giuseppe
7. Costa Dino
8. Crupi Vincenza
9. Cutroni Maria
10. D‘Angelo Giovanna
11. Di Salvo Rachele Anna
12. Giaquinta Paolo Vittorio
13. Giardina Giorgio
14. Ginatempo Beniamino
15. Gucciardi Pietro
16. Iatì Maria Antonia
17. Magazù Salvatore
18. Maisano Giacomo
19. Majolino Domenico
20. Malescio Gianpietro
21. Mandanici Andrea
22. Maragò Onofrio
23. Micali Norberto
24. Mondio Guglielmo
25. Moricciani Dario
26. Prestipino Giarritta Santi
27. Saija Franz
28. Torrisi Lorenzo
29. Trifirò Antonio
30. Tripodo Gaspare
31. Wanderlingh Ulderico
mcabramo@unime.it;
renato.barna@me.infn.it;
borghese@ortica.unime.it;
cbranca@unime.it;
carlo.caccamo@unime.it;
carini@unime.it;
dcosta@unime.it;
vincenza.crupi@unime.it;
Maria.Cutroni@unime.it;
gdangelo@unime.it;
Rachele.disalvo@roma2.infn.it;
paolo.giaquinta@unime.it;
giardina@nucleo.unime.it;
Beniamino.Ginatempo@unime.it;
gucciardi@me.cnr.it;
iati@me.cnr.it;
smagazu@unime.it;
giacomo.maisano@unime.it;
Domenico.Majolino@unime.it;
malescio@unime.it;
amandanici@unime.it;
marago@me.cnr.it;
micali@me.cnr.it;
mondio@ortica.unime.it;
Dario.Moricciani@roma2.infn.it;
sprestipino@unime.it;
saija@me.cnr.it;
lorenzo.torrisi@unime.it;
atrifiro@unime.it;
gtripodo@unime.it;
ulderico.wanderlingh@unime.it;
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
135
ELENCO DOTTORANDI DI RICERCA IN FISICA:
XXIV CICLO Curriculum
D‘ANDREA Cristiano Struttura della Materia dandrea@its.me.cnr.it
FINA Natale Struttura della Materia nfina@unime.it
RIFICI Simona Struttura della Materia srifici@tiscalinet.it
SCARDINA Francesco Fisica Nucleare scardinaf@lns.infn.it
TRIMARCHI Antonio Struttura della Materia antotrimarchi@unime.it
VILARDI Rocco Struttura della Materia roccovilardi@alice.it
XXV CICLO
CACCIOLA Adriano Struttura della Materia adrianocacciola@tiscali.it
DI BARTOLO Federico Fisica Nucleare fdibartolo@unime.it
FISICHELLA Maria Fisica Nucleare fisichella@lns.infn.it
MINNITI Triestino Fisica Nucleare tminniti@unime.it
ROMANIUK Mariia Fisica Nucleare romanyukmariya@ukr.net
SANTORO Simone Fisica Nucleare ssantoro@unime.it
XXVI CICLO
CURCIARELLO Francesca Fisica Nucleare curciarello@unime.it
CUTRONEO Mariapompea Struttura della Materia mcutroneo@unime.it
DE LEO Veronica Fisica Nucleare verydeleo@hotmail.com
SAYED Rania Strutt. della Materia rania_sayed80@yahoo.com
STASSI Roberto Struttura della Materia robertostassi@gmail.com
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
136
Tesi del Dottorato di Ricerca in Fisica
Ciclo XXIV
XXIV CICLO
DOTTORANDO CURRICULUM ARGOMENTO TESI TUTORE / CO-TUTORE
Dott. D‘Andrea
Cristiano Struttura della Materia Surface enhanced Raman spectroscopy di proteine
Dott. Pietro G.Gucciardi
Prof. Fortunato Neri
Dott. Fina
Natale Struttura della Materia
Nano-ottica: diffusione ed emissione di luce in
presenza di nanoparticelle metalliche.
Prof. Guglielmo Mondio
Dott. Salvatore Savasta
Dott.ssa Rifici
Simona Struttura della Materia
Struttura delle biomembrane investigata tramite la
spettroscopia NMR e la diffrazione di raggi X.
Prof. Ulderico
Wanderlingh
Dott. Scardina
Francesco Fisica Nucleare
Dynamics of the quark-gluon plasma in ultra-
relativistic heavy-ion collision. A transport theory
for the interaction between the minijets and the bulk
of the plasma.
Prof. Giorgio Giardina
Prof. Vincenzo Greco
Dott. Trimarchi
Antonio Struttura della Materia
Struttura e dinamica di biomembrane investigate
con small angle X-Ray scattering e spettroscopia di
neutroni.
Prof. Ulderico
Wanderlingh
Dott. Vilardi
Rocco Struttura della Materia
Interazione radiazione materia in regime non
perturbativo.
Prof. Ezio Bruno
Dott. Salvatore Savasta
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
137
Pubblicazioni 2011
degli studenti del Dottorato di
Ricerca in Fisica
dell’Università di Messina
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
138
PUBBLICAZIONI 2011 XXIV Ciclo
Cristiano D’Andrea
1. Re-Radiation Enhancement in polarized Surface-Enhanced Resonant Raman Scattering of Randomly Oriented
Molecules on Self-Organized Gold Nanowires, B. Fazio, C. D‘Andrea, F. Bonaccorso, A. Irrera, G. Calogero,
C. Vasi, P.G. Gucciardi, M. Allegrini, A. Toma, D. Chiappe, C. Martella, and F. Buatier de Mongeot, ACS
NANO, Vol 5, No 7 (2011) Pag. 5947-5956;
2. Manipulation and Raman Spectroscopy with Optically Trapped Metal Nanoparticles Obtained by Pulsed Laser
Ablation in Liquids, E. Messina, E. Cavallaro, A. Cacciola, R. Saija, F. Borghese, P. Denti, B. Fazio, C.
D‘Andrea, P. G. Gucciardi, M. A. Iati, M. Meneghetti, G. Compagnini, V. Amendola, and O.M. Maragò,
Journal of Physical Chemistry C 115 Issue 12 (2011) Pag. 5115-5122;
3. SERS activity of pulsed laser ablated silver thin films with controlled nanostructure E. Fazio, F. Neri, C.
D‘Andrea, P. M. Ossi, N. Santo and S. Trusso Journal of Raman Spectroscopy 42 (2011) Pag. 1298-1304;
4. Synthesis by pulsed laser ablation in Ar and SERS activity of silver thin films with controlled nanostructure, C.
D‘Andrea, F. Neri, P. M. Ossi, N. Santo and S. Trusso, Laser Physics 21 Issue 4 (2011) Pag 818-822.
5. Spectral dependence of the Amplification Factor in SERS (Poster), C. D‘Andrea, B. Fazio, A. Irrera, P. Artoni,
O.M. Maragò, M. A. Iatì, G. Calogero, P. G. Gucciardi, Proceedings International Summer School on
―Plasmonics, Functionalization and Biosensing‖, Kirchhoff Institute for Physics, University of Heidelberg, 24-
30 Aprile 2011;
6. Spectral dependence of the Amplification Factor in Surface Enhanced Raman Spectroscopy (Poster), C.
D‘Andrea, B. Fazio, A. Irrera, P. Artoni, O.M. Maragò, M. A. Iatì, G. Calogero, P. G. Gucciardi, Proceeedings
International Summer School on "NANO-OPTICS: Plasmonics, Photonic Crystals, Metamaterials and Sub-
Wavelength Resolution", Ettore Majorana Foundation and Centre for Scientific Culture, Erice (TP), 03-18
Luglio 2011;
7. Spectral dependence of the Amplification Factor in Surface Enhanced Raman Spectroscopy (Poster), C.
D‘Andrea, B. Fazio, A. Irrera, P. Artoni, O.M. Maragò, M. A. Iatì, G. Calogero, P. G. Gucciardi, Proceedinggs
Electromagnetic and Light Scattering XIII, Conference, Taormina 26-30 Settembre 2011.
Natale Fina
1. A.Ridolfo, N.Fina, O.Di Stefano, O.M. Maragò , S.Savasta. Photoluminescence from a Dimer Nanoantenna:
From Purcell Effect to Nanopolaritons. in Progress on ACS Nano.
Simona Rifici
1. S. Rifici, C. Crupi, G. D‘Angelo, G. Di Marco, G. Sabatino, V. Conti Nibali, A. Trimarchi and U.
Wanderlingh, “Effects of a short length alcohol on dimyristoylphosphatidylcholine system”, Philosophical
Magazine, 91 2014-2020, (2011);
2. S. Rifici, U. Wanderlingh, G. D‘Angelo, C. Crupi, A. Trimarchi, V. Conti Nibali, “Effects of medium-chain
alcohols on the structure of phospholipid bilayers”, Il Nuovo Cimento, in press.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
139
Francesco Scardina
1. ―Impact of temperature dependence of the energy loss on jet quenching observables‖
F. Scardina, M. Di Toro, V. Greco. Oct 2011. 7 pp.
Published in Nuovo Cim. C34N2 (2011) 67-73
Antonio Trimarchi
1. S. Rifici, C. Crupi, G. D‘Angelo, G. Di Marco, G. Sabatino, V. Conti Nibali, A. Trimarchi and U.
Wanderlingh, ―Effects of a short length alcohol on dimyristoylphosphatidylcholine system‖, Philosophical
Magazine, 91 2014-2020, (2011);
2. S. Rifici, U. Wanderlingh, G. D‘Angelo, C. Crupi, A. Trimarchi, V. Conti Nibali, “Effects of medium-chain
alcohols on the structure of phospholipid bilayers”, Il Nuovo Cimento, IN PRESS;
3. U. Wanderlingh, G. D‘Angelo, V. Conti Nibali, A. Trimarchi, C. Crupi ―Anisotropic dynamics in phosholipid
membranes, a Fixed Energy Window neutron scattering study”, J. Chem. Phys. In press.
Rocco Vilardi
1. R. Vilardi, A. Ridolfo, S. Portolan, S. Savasta, O. Di Stefano, Quantum Complementarity of Cavity Photons
Coupled to a Three-Level System, to be published by Physical Review A;
2. Rocco Vilardi, articolo riguardante il trasferimento della coerenza, prossima pubblicazione su Le Scienze Web
News, ISSN 1827-8922;
3. Rocco Vilardi, articolo riguardante il progetto ELENA, prossima pubblicazione su Le Scienze Web News,
ISSN 1827-8922;
4. Rocco Vilardi, Alla ricerca del bosone di Higgs: nuova fisica al CERN?, Le Scienze Web News, 25 luglio
2011, ISSN 1827-8922;
5. Rocco Vilardi, Alessandro Ridolfo, Salvatore Savasta, Controllo ottico ultraveloce del dualismo onda
corpuscolo, Le Scienze Web News, 28 marzo 2011, ISSN 1827-8922;
6. A. Ridolfo, R. Vilardi, O. Di Stefano, S. Portolan, and S. Savasta, All Optical Switch of Vacuum Rabi
Oscillations: The Ultrafast Quantum Eraser, Physical Review Letters 106, 013601, January 05 2011;
7. Rocco Vilardi, Alessandro Ridolfo, Ultrafast Optical Control of vacuum Rabi Oscillations of a MicroCavity-
Single Quantum Emitter System, ACTIVITY REPORT 2010, pp.69-72, Lorenzo Torrisi Editore, Dottorato di
Ricerca in Fisica, Università degli Studi di Messina, c/o Dipartimento di Fisica, facoltà di Scienze-Università
di Messina, ISSN 2038-5889.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
140
PUBBLICAZIONI 2011 XXV Ciclo
Adriano Cacciola
1. Manipulation and Raman Spectroscopy with Optically Trapped Metal Nanoparticles Obtained by Pulsed Laser
Ablation in Liquids, Messina E, Cavallaro E, Cacciola A, et al., JOURNAL OF PHYSICAL CHEMISTRY C
Volume: 115 Issue: 12 Pages: 5115-5122 Published: MAR 31 2011;
2. Plasmon-Enhanced Optical Trapping of Gold Nanoaggregates with Selected Optical Properties, Messina E,
Cavallaro E, Cacciola A, et al., ACS NANO Volume: 5 Issue: 2 Pages: 905-913 Published: FEB 2011;
3. Stratified dust grains in the interstellar medium. III Infrared cross-sections, Author(s): Iati M. A.; Cecchi-
Pestellini C.; Cacciola A.; et al., 12th International Conference on Electromagnetic and Light Scattering by
Nonspherical Particles - Theory, Measurements, and Applications, J. of Quantitative Spectroscopy & Radiative
Transfer, Volume: 112 Issue: 11 Special Issue: SI Pages: 1898-1906, 2011.
Federico Di Bartolo
1. L.Torrisi; L. Giuffrida, D. Margarone, F. Caridi, F. Di Bartolo, Low energy proton beams from laser-generated
plasma, NIM in Physics A, 653, 140T (2011);
2. L. Torrisi, F. Caridi, F. Di Bartolo, A. Baglione, M. Cutroneo, Ion Production and Detection from Laser-Thin
Targets Interaction, IEEE Transactions on Plasma Science, in press.;
3. F. Di Bartolo, F. Caridi, L. Torrisi, Mass Quadrupole Spectrometry applied to laser ion sources, Nucleonika.,
in press;
4. G. Castro, D. Mascali, F.P. Romano, L. Celona, S. Gammino, N. Gambino, D. Lanaia, R. Di Giugno, R.
Miracoli, T. Serafino, F. Di Bartolo and G. Ciavola, Comparison between off-resonance and Electron
Bernstein Waves heating regime in a Microwave Discharge Ion Source, Rev. Sc. Instr., (2011) in press.;
5. G. Castro, F. Di Bartolo, N. Gambino, D. Mascali, A. Anzalone, L. Celona, S. Gammino, R. Di Giugno, D.
Lanaia, R. Miracoli, F.P. Romano, T. Serafino, S.Tudisco, Ion acceleration in non-equilibrium plasmas driven
by fast drifting electron, Appl. Surf. Sc. (2011);
6. L. Torrisi, S. Cavallaro, S. Gammino, L. Andò, P. Cirrone, M. Cutroneo, R. Sayed, L. Giuffrida, F. Romano, F.
Caridi, F. Di Bartolo, A.M. Visco, A. Baglione, C. Scolaro, Proton generation from LIS at INFN-LNS
(LIANA project), INFN-LNS ACTIVITY REPORT 2010;
Maria Fisichella
1. Analysis of states in 13
C populated in 9Be +
4He resonant scattering
M. Freer, N. I. Ashwood, N. Curtis, A. Di Pietro, P. Figuera, M. Fisichella, L. Grassi, D. Jelavic Malenica,
Tz. Kokalova, M. Koncul, T. Mijatovic M. Milin, L. Prepolec, V. Scuderi, N. Skukan, N. Soic, S. Szilner, V.
Tokic D. Torresi, and C. Wheldon, Phys. Rev. C 84, 034317 (2011)
2. Fusion and direct reactions for the system 6He + 64Zn at and below the Coulomb barrier
V. Scuderi, A. Di Pietro, P. Figuera, M. Fisichella, F. Amorini, C. Angulo, G. Cardella, E. Casarejos, M.
Lattuada, M. Milin, A. Musumarra, M. Papa, M. G. Pellegriti, R. Raabe, F. Rizzo, N. Skukan, D. Torresi,
M. Zadr, Phys. Rev. C to be published
3. Li-α cluster states in 12B using 8Li + 4He inverse kinematics elastic scattering
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
141
D. Torresi, L. Cosentino, A. Di Pietro, C. Ducoin, P. Figuera, M. Fisichella, M. Lattuada, T. Lonnroth, C.
Maiolino, A. Musumarra, M. Papa, M.G. Pellegriti, M. Rovituso, D. Santonocito, G. Scalia, V. Scuderi and E.
Strano, M. Zadro, International Journal of Modern Physics E Vol. 20, No. 4 (2011) 1026–1029
4. Structure effects in the reactions 9,10,11
Be+64
Zn at the Coulomb barrier
V. Scuderi, A. Di Pietro, L. Acosta, F. Amorini, M.J.G. Borge, P. Figuera, M. Fisichella, L.M. Fraile,
J.Gomez-Camacho, H. Jeppesen, M. Lattuada, I. Martel, M. Milin, A. Musumarra, M. Papa, M.G. Pellegriti,
F. Perez-Bernal, R. Raabe, G. Randisi, F. Rizzo, D. Santonocito, G. Scalia, O. Tengblad, D. Torresi, A.M.
Vidal, M Zadro, Journal of Physics: Conference Series 267 (2011) 012012
5. Alpha structure of 12
B studied by elastic scattering of 8Li EXCYT beam on
4He thick target
M.G. Pellegriti, D. Torresi, L. Cosentino, A. Di Pietro, C. Ducoin, M. Lattuada, T. Lonnroth, P. Figuera, M.
Fisichella, C. Maiolino, A. Musumarra, M. Papa, M. Rovituso, V. Scuderi, G. Scalia, D. Santonocito, M.
Zadro, Journal of Physics: Conference Series 267 (2011) 012011
6. Halo effects on fusion cross section in 4,6
He+64
Zn collision around and below the coulomb barrier
M Fisichella, V Scuderi, A Di Pietro, P Figuera, M Lattuada, C Marchetta, M Milin, A Musumarra, M G
Pellegriti, N Skukan, E Strano, D Torresi, M Zadro, Journal of Physics: Conference Series 282 (2011) 012014
7. Structure effects and dynamics in fusion reactions of light weakly bound nuclei
E. Strano, A. DiPietro, P. Figuera, M. Fisichella, M. Lattuada, C. Maiolino, A. Musumarra, M G Pellegriti, D
Santonocito, V Scuderi, D Torresia, M Zadro, Journal of Physics: Conference Series 282 (2011) 012020
8. Fusion cross-section in the 4,6He + 64Zn collisions around the Coulomb barrier
M. Fisichella, Il Nuovo Cimento vol. 34C, 5 (2011)
Tino Minniti
1. T. Minniti and S. Santoro, ―Study of Nuclear equations of state:The ASY-EOS experiment at GSI‖
Activity Report 2010, Dottorato di Ricerca in Fisica, Università di Messina,. Torrisi Ed., 81-85, ISSN2038-
5889, 2011
Maria Romaniuk
1. M.V.Romaniuk, G.Giardina, G.Mandaglio, M.Manganaro, Meson Photoproduction and Baryon Resonances at
BGOOD , Activity report 2010 , Università di Messina, ISSN 2038-5889 (2010) 95-98;
2. V.S.Olkhovsky, M.V.Romaniuk, Non-relativistic-particle and photon two-dimensional above-barrier
penetration and sub-barrier tunneling through a barrier between initial and final free-motion regions along axis
normal to both planar interfaces, Journal of Modern Physics, 2011, 2, 1166-1171,
doi:10.4236/jmp.2011.210145. Published Online October 2011 G. Giardina, A. K. Nasirov, G. Mandaglio, F.
Curciarello,V. De Leo, G. Fazio, M. Manganaro, M. Romaniuk, C. Saccà, Investigation on the quasifission
process by theoretical analysis of experimental data of fissionlike reaction products, Journal of Physics:
Conference Series 282 (2011) 012006, doi:10.1088/1742-6596/282/1/012006;
Simone Santoro
1. I.Lombardo, L.Acosta, C.Agodi, F.Amorini, A.Anzalone, L.Auditore, I.Berceanu, G.Cardella, S.Cavallaro,
.B.Chatterjee, E.De Filippo, G.Giuliani, E.Geraci, L.Grassi, J.Han, E.La Guidara, G.Lanzalone, D.Loria,
C.Maiolino, T.Minniti, A.Pagano, M.Papa, S.Pirrone, G.Politi, F.Porto, F.Rizzo, P.Russotto, S.Santoro,
A.Trifirò, M.Trimarchi, G.Verde, M.Vigilante
“N/Z effects on evaporation residue emission near fragmentation treshold”
Proceeding of 14th
International Conference on Information Fusion, FUSION 2011, JUL 5-8 2011, Chicago
ILLINOIS USA - EPJ Web of Conferences 17 (2011) 16005
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
142
2. S. Santoro for CHIMERA and ASY-EOS Collaboration
“Study of nuclear equations of state: the ASY-EOS experiment at GSI”
Second International Symposium on Nuclear Symmetry Energy, NuSYM11, June 17-20 2011, at Smith
College in Northampton, Massachusetts, USA.
3. S.Santoro for ASY-EOS Collaboration
“Study of nuclear Equation Of State (EOS): the ASY-EOS experiment at GSI”
The Nuclear Chemistry Gordon Research Conference, June 12-17 2011 Colby-Sawyer College, New London,
New Hampshire, USA.
4. S.Santoro for ASY-EOS Collaboration
“ASY-EOS experiment at GSI: Chimera results”
ASYEOS collaboration meeting during the International Workshop on Multifragmentation and Related Topics
– 2011 at GANIL from 2nd
to 5th
November 2011, Caen, France.
5. G.Cardella, L.Acosta, C.Agodi, F.Amorini, A.Anzalone, L.Auditore, I.Berceanu, M.BChatterjiee, E.DeFilippo,
L.Grassi, E.La Guidara, G.Lanzalone, I.Lombardo, D.Loria, T.Minniti, A.Pagano, M.Papa, S.Pirrone, G.Politi,
F.Porto, F.Rizzo, E.Rosato, P.Russotto, S.Santoro, A.Trifirò, M. Trimarchi, G.Verde, M.Vigilante
“Reactions with exotic beams using the CHIMERA detector at LNS”
Conference on Structure and Dynamics of Nuclei far from Stability, September 15-16 2011, Dipartimento di
Fisica e Astronomia dell‘Università di Catania.
6. G.Cardella, L.Acosta, C.Agodi, F.Amorini, A.Anzalone, L.Auditore, I.Berceanu, M.BChatterjiee, E.DeFilippo,
L.Grassi, E.La Guidara, G.Lanzalone, I.Lombardo, D.Loria, T.Minniti, A.Pagano, M.Papa, S.Pirrone, G.Politi,
F.Porto, F.Rizzo, E.Rosato, P.Russotto, S.Santoro, A.Trifirò, M. Trimarchi, G.Verde, M.Vigilante
“Use of fragmentation beams at LNS with CHIMERA detector”
International Workshop on Multifragmentation and Related Topics – 2011 at GANIL from 2nd
to 5th
November
2011, Caen, France.
7. L. Acosta, T. Minniti, G. Cardella, G. Verde, F. Amorini, A. Anzalone, L. Auditore, M. Buscemi, A. Chbihi,
E. De Filippo, L. Francalanza, E. Geraci, C. Guazzoni, E. La Guidara, G. Lanzalone, I. Lombardo, S. Lo
Nigro, D. Loria, C. Maiolino, I. Martel, E.V. Pagano, A. Pagano, M. Papa, S. Pirrone, G. Politi, F. Porto, F.
Rizzo, P. Russotto, A.M. SánchezBenítez, J.A. Dueñas, R. Berjillos, S. Santoro, A. Trifirò, M. Trimachi, M.
Venhart, M. Veselsky, M. Vigilante
“FARCOS, a new array for femtoscopy and correlation spectroscopy”
International Workshop on Multifragmentation and Related Topics – 2011 at GANIL from 2nd
to 5th
November
2011, Caen, France.
8. S. Santoro per la collaborazione ASY-EOS
“Study of nuclear Equation Of State: the ASY-EOS experiment at GSI”
Società Italiana di Fisica – XCVII Congresso Nazionale, L‘Aquila, 26-30 Settembre 2011, p.35
9. Acosta L., Agodi C., Amorini F., Anzalone A., Auditore L., Bardelli L., Berceanu I., Cardella G., Chatterjee
M.B., De Filippo E., Grassi L., La Guidara E., Lanzalone G., Lombardo I., Loria D, Minniti T., Pagano A.,
Papa M., Pirrone S., Politi G., Porto F., Rizzo F., Russotto P., Santoro S., Trifirò A., Trimarchi M, Verde G.,
Vigilante M., “Misure con fasci di frammentazione ai LNS“
Società Italiana di Fisica – XCVII Congresso Nazionale, L‘Aquila, 26-30 Settembre 2011, p.174
10. Acosta L., Amorini F., Anzalone A., Auditore L., Cardella G., Chbihi A., De Filippo E., Francalanza L.,
Geraci E., Guazzoni C., La Guidara E., Lanzalone G., Lombardo I., Lo Nigro S., Loria D., Martel I., Minniti
T., Pagano E.V., Pagano A., Papa M., Pirrone S., Politi G., Porto F.,Rizzo F.,Russotto P.,Santoro S., Trifirò A.,
Trimarchi M.,Verde G., Venhart M., Veselsky M., Vigilante M., “Il progetto FARCOS/EXOCHIM.”
Società Italiana di Fisica – XCVII Congresso Nazionale, L‘Aquila, 26-30 Settembre 2011, p.176
11. Acosta L., Amorini F., Anzalone A., Auditore L., Cardella G., Chbihi A., De Filippo E., Francalanza L.,
Geraci E., Guazzoni C., La Guidara E., Lanzalone G., Lombardo I., Lo Nigro S., Loria D., Martel I., Minniti
T., Pagano E.V., Pagano A., Papa M., Pirrone S., Politi G.,Porto F., Rizzo F.,Russotto P.,Santoro S., Trifirò A.,
Trimarchi M., Verde G.,Venhart M., Veselsky M., Vigilante M.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
143
“Dinamica e spettroscopia da studi di correlazioni con FARCOS/CHIMERA.”
Società Italiana di Fisica – XCVII Congresso Nazionale, L‘Aquila, 26-30 Settembre 2011, p.177
12. F. Amorini, R. Bassini, C. Boiano, G. Cardella, E. De Filippo, L. Grassi, C. Guazzoni, Member, IEEE, P.
Guazzoni, M. Kiš, E. La Guidara, Y. Leifels, I. Lombardo, T. Minniti, A. Pagano, M. Papa, S. Pirrone, G.
Politi, F. Porto, F. Riccio, F. Rizzo, P. Russotto, S. Santoro, W. Trautmann, A. Trifirò, G. Verde, P. Zambon,
Student Member, IEEE, L. Zetta
“Light Charged Particle Identification by Means of Digital Pulse Shape Acquisition in the CHIMERA CsI(Tl)
Detectors at GSI Energies”, submitted paper on IEEE Transactions, to be published.
PUBBLICAZIONI 2011 XXVI Ciclo
Francesca Curciarello
1. G. Giardina, A. K. Nasirov, G. Mandaglio, F. Curciarello, V. De Leo, G. Fazio, M. Manganaro, M. Romaniuk,
C. Saccà: ―Investigation on the quasifission process by theoretical analysis of experimental data of fissionlike
reaction products‖, J. Phys.: Conf. Ser. 282, 012006 (1-20) (2011);
2. G. Fazio, G. Mandaglio, V. De Leo and F. Curciarello: “The Abrupt changes of the yellowed fibrils density on
the Linen of Turin”, Rad. Eff. and Def. in Solids, iFirst (2011);
3. O. Povoroznik, O. K. Gorpinich, O. O. Jachmenjov, H. V. Mokhnach, O. Ponkratenko, G. Mandaglio, F.
Curciarello, V. De Leo, G. Fazio and G. Giardina: ―High-lying 6Li levels at exicitation energy of around 21
Mev”, J. Phys. Soc. Jpn. 80 (2011) 094204.
Mariapompea Cutroneo
1. L. Torrisi, S. Cavallaro, M. Cutroneo, D. Margarone, S. Gammino
―Proton emission from a laser ion source‖
Participation to 14 th
ICIS 2011 Int. Conference, 12-16 Sept., Giardini Naxos (ME), Italy,
Accepted from Review of Scientific Instruments, 2011, in press.
2. D. Margarone, J. Krasa, J. Prokupek, A. Velyhan, L. Torrisi, A. Picciotto, L.Giuffrida, S.
Gammino, P. Cirrone, M. Cutroneo, F. Romano, E. Serra, A. Mangione, M. Rosinski, P.
Parys, L. Ryc, J. Limpouch, L. Laska, K. Jungwirth, J. Ullschmied, T. Mocek, G. Korn
and B. Rus
―New methods for high current fast ion beam production by laser-driven acceleration‖
Participation to 14 th
ICIS 2011 Int. Conference, 12-16 Sept., Giardini Naxos (ME), Italy,
Accepted from Rev. Sci. Instr., 2011, in press.
3. L. Torrisi, S. Cavallaro, M. Cutroneo, L. Giuffrida, J. Krasa, D. Margarone, A. Velyhan,
J. Kravarik, J. Ullschmied, J. Wolowski, A. Szydlowski, M. Rosinski
―Monoenergetic proton emission from nuclear reaction induced by high intensity laser-
generated plasma‖, Participation to 14 th
ICIS 2011 Int. Conference, 12-16 Sept., Giardini Naxos (ME), Italy,
Accepted from Review of Scientific Instruments, 2011, in press.
4. L. Torrisi, A. Italiano, E. Amato, F. Caridi, M. Cutroneo, C.A. Squeri, G. Squeri and A.M.
Roszkowska
―Radiation effects on poly(methyl methacrylate) induced by pulsed laser irradiations.
Radiation Effects & Defects in Solids 2011, in press.
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
144
5. M. Cutroneo, Relazione su invito alla Conferenza: ―X Giornata di Studio BIOINGEGNERIA - Facoltà di
Ingegneria Università di Catania - 1 luglio 2011‖ col lavoro: ―Fisica dei laser e loro interazione con la
materia‖, Proceeding 2011 in press.
6. Proceedings Conferenza 5th
PPLA (Plasma Production by Laser Ablation), Catania, 21-23 Set. 2011, col lavoro
―Laser ablation coupled to mass quadrupole spectrometer (LAMQS) and X-rays fluorescence for applications
in cultural heritage‖, in press.
7. Proceedings Conferenza 5th
PPLA (Plasma Production by Laser Ablation), Catania, 21-23 Set. 2011, col lavoro
―Proton emission from resonant laser absorption and self-focusing effects from hydrogenated structures”, in
press.
8. Proceedings Conferenza 5th
PPLA (Plasma Production by Laser Ablation), Catania, 21-23 Set. 2011, col lavoro
―XPS and XRF depth patina profiles of ancient silver coins‖, in press.
Veronica De Leo
1. G. Giardina, A.K. Nasirov, G. Mandaglio, F. Curciarello, V. De Leo, G. Fazio, M. Manganaro, M. Romaniuk,
C. Saccà, Investigation on the quasifission process by theoretical analysis of experimental data of fissionlike
reaction products, Journal of Physics: Conference Series 282 (2011) 012006;
2. O. Povoroznyck, O.K. Gorpinich, O. O. Jachmenjov, H.V. Mokhnach, O.Ponkratenko, G.Mandaglio,
F.Curciarello, V. De Leo, G. Fazio, and G. Giardina, ―High-Lying 6Li Levels at Exicitation energy of around
21 Mev‖, J. Phys. Soc. Jpn. 80 (2011) 094204;
3. G. Fazio, G. Mandaglio, V. De Leo and F. Curciarello: ―The Abrupt changes in the yellowed fibril density in
the Linen of Turin‖, Rad. Eff. and Def. in Solids, iFirst (2011).
Rania Sayed
1. M. G. Donato, P. G. Gucciardi, S. Vasi, M. Monaca, R. Sayed, G. Calogero, P.H. Jones, O.M. Maragò,
"Raman optical trapping of carbon nanotubes and graphene", Proceedings of CARBOMAT 2011, Catania, 5th-
7th December 2011;
2. Proceedings accepted for a poster presentation at CARBOMAT 2011, Workshop on Carbon-based
low-dimentional Materials, Catania, 5th-7th December, 2011.
Roberto Stassi
1. O. Di Stefano, R. Stassi, A. Ridolfo, S. Patané, and S. Savasta, Phys.Rev. B 84, 085324 (2011)
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
145
Foto
2a Giornata di Studio
del
Dottorato di Ricerca in Fisica
dell‘Università di Messina
8 Novembre 2011,
Facoltà di Scienze M.M.F.F.N.N.
Biblioteca Centralizzata
V.le F. S. D‘Alcontres 31
S. Agata, Messina
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
155
INDICE AUTORI
Artoni P pag. 89
Aversa M C 13
Cacciola D 21
Calogero G 61, 89
Caridi F 25, 55
Castro G 25
Celona L 25
Colonna M 101
Curciarello F 37, 65, 77
Cutroneo M 71
D‘Andrea C 61, 89
De Leo V 37, 65, 77
Di Bartolo F 25
Di Giugno R 25
Di Pietro A 31
Di Stefano O 85, 93
Di Toro M 101
Donato M G 81
Donato P 49
Fazio B 61, 89
Figuera P 31
Fina N 93
Fisichella M 31
Gammino S 25
Giaquinta P V 47
Giardina G 37, 65, 77
Greco V 101
Gucciardi P G 61, 81, 89
Irrera A 89
Lanaia D 25
Lattuada M 31
Magaudda D 15
Mandaglio G 37, 65, 77
Maragò O M 61, 81, 89, 93
Marchetta C 31
Mascali D 25
Micali N 61
Minniti T 33
Miracoli R 25
Musumarra A 31
Pellegriti M G 31
Ridolfo A 93
Rifici S 97
Romaniuk M 37, 65, 77
Ruiz C 31
Santoro S 41
Savasta S 85, 93, 109
Sayed R 81
Scardina F 101
Scuderi V 31
Shotter A 31
Stassi R 85
Strano E 31
Torresi D 31
Torrisi L 9, 25, 55, 71
Trimarchi A 105
Vilardi R 109
Villari V 61
Volpe G 81
Zadro M 31
Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
159
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Activity Report 2011 – Dottorato di Ricerca in Fisica, Università di Messina
160
Dottorato di Ricerca in Fisica
Facoltà di Scienze
Dipartimento di Fisica
Università di Messina
V.le F. Stagno D’Alcontres
S. Agata, Messina, Italy
Phone: +39 090 6765052
Fax: +39 090 395004
e-mail: Lorenzo. Torrisi@unime.it
ISSN 2038-5889