John T. Costello

John T. CostelloNational Centre for Plasma Science & Technology (NCPST)/

School of Physical Sciences, Dublin City Universitywww.physics.dcu.ie/~jtc

Two Colour and Two Photon Ionization Processes in Intense

XUV and Optical Fields at FLASH

UXSS - SLAC. June 18, 2009

' FLASH ' - Free Electron LASer in Hamburg

http://www.physics.dcu.ie/~jtc

LIXAM (Orsay): D. Cubaynes, M. Meyer

Universite Paris 06 (PMC): R. Taieb, A. Maquet

DESY (Hamburg): A. Azima, S. Düsterer, P. Radcliffe, H. Redlin, W-B Li, J. Feldhaus

PTB (Berlin): A. A. Sorokin, M. Richter

Moscow State University: A. N. Grum-Grzhimailo, E. V. Gryzlova, S. I. Strakhova

Queen’s University Belfast: Hugo van der Hart

Dublin City University: J. Dardis, P. Hayden, P. Hough, T. Kelly, V. Richardson, E. T. Kennedy, J. T. Costello

Thanks to AG Photon (R Treusch et al.) & AG Machine (M Yurkov et al.)

Acknowledgements


DCU Intense Laser Matter Research

Academic Staff (5): John T. Costello, Eugene T. Kennedy, Jean-Paul Mosnier, Lampros Nikolopoulos and Paul van Kampen

Current Postdocs (2):Dr. Patrick Hayden, Dr. Sateesh Krishnamurty (Incoming - Subhash Singh)

Current PhD students (13 + 1): John Dardis, Jack Connolly, Brian Doohan, Colm Fallan, Padraig Hough, Eanna Mac Carthy, , Mossy Kelly, Conor McLaughlin, Ricky O'Haire,Vincent Richardson, Dave Smith, Tommy Walsh & Jiang Xi, open position (with LN)

Recent PhD Graduates: Caroline Banahan, Mark Stapleton, Jonathan Mullen, Kevin Kavanagh, Eoin O’Leary

Recent Postdocs: Deirdre Kilbane, Hugo de Luna, Jofre Gutieriez-Pedrogosa, Brendan Doggett, Subo Chakraborti and Jean-Rene Duclere

6 laboratory areas focussed on pulsed laser matter interactions (NIR – X-ray/ 30fs – 30 ns, spectroscopy/ imaging/PLD)

Funded by:SFI - Frontiers and InvestigatorHEA – PRTLI (Kit)IRCSET (People)EU - Marie Curie (People)


DCU Intense Laser Matter Research


Research Domains:•Photoionization of Atoms and Ions with Laser Plasma, Synchrotron and Free Electron Laser Light Sources (JC, PVK, ETK, LN)•Optical Diagnostics of Laser Produced Plasmas (JC)•Laser Induced Breakdown Spectroscopy – LIBS (JC, ETK)•Pulsed Laser Deposition (PLD) of Materials (JPM)

Some Current Projects:•Two colour photoionization of atoms with XUV FELs (& LPLS)•UV-Vis imaging, spectroscopy and interferometry of colliding laser produced plasmas (with Sivandan ‘Hari’ Harilal, Purdue)•Colliding plasma targets for EUVL light sources (with UCD & TCD)•VUV-LIBS for Elemental Characterisation in Steel•PLD and in-situ P-type doping of ZnO nanostructures

6 laboratory areas focussed on pulsed laser matter interactions (NIR – X-ray/ 30fs – 30 ns, spectroscopy/ imaging/PLD)

Collaboration grew out of EU RTD Project:HRPI-CT-1999-50009

Title: “X-Ray FEL Pump Probe Facility”

Partners: Orsay, DCU, Lund, MBI, BESSY & DESY

Collaboration - Origin


1. Few-photon single and multiple ionization processes

2. Ultra-dilute targets

3. Photo-processes with ultralow cross-sections

4. Pump and probe experiments (XUV + XUV or XUV + Opt.)

1. Single shot measurements

2. Brings inner-shell electrons into non-linear processes

3. Re-asserts primacy of the photon over field effects* !

What are the USPs of XFELs in AMOP ?


*See USP No. 1

• FLASH (Brief) Overview

• Atoms in Intense XUV + NIR Fields 1. Coherent Photoionization Processes in Superposed Fields 2. Few Femtosecond X-ray Photoionization Processes at LCLS

• Two Photon Ionization in Intense XUV Fields

• Next Steps

Outline of the Talk


Part 1 - FLASH Overview


300 m

FLASH Overview

• Energy range: ~ 0.3 – 1 GeV ~

6.5 – 60 nm

LaserBunch

CompressorBypass

UndulatorsCollimator

Bunch Compressor

5 MeV 127 MeV 450 MeV 1000 MeV

Accelerating StructuresDiagnostics

FEL Diagnostics

RF-gun


water windowWavelength range (fundamental): 6 - 60 nm

FEL harmonics (@13.7 nm): 3 rd : 4.6 nm (270 eV) 5 rd : 2.7 nm (450 eV)

Spectral width (FWHM): 0.5-1 %

Pulse energy: up to 50 µJ (average), 120 µJ (peak)

Pulse duration (FWHM): 10-30 fs

Peak power (fundamental): Few GW

Average power (fundamental): 0.1 W (up to 3000 pulses /sec)

Photons per pulse: ~ 1013

FLASH: Key Performance Indicators

Ackermann et al., Nature Photonics 1 336 (2007)

FEL output builds up from spontaneous emission (photon noise) => SASE – ‘Self Amplified Spontaneous Emission’

O/P Profile and Spectral Distribution

Spectral Fluctuations Temporal Fluctuations


FEL output builds up from spontaneous emission (photon noise) => SASE – ‘Self Amplified Spontaneous Emission’

O/P Profile and Spectral Distribution

Raw XUV Spectrum Corrected XUV Spectrum


Part 2 - Experiments on dilute targets with FLASH

Motivations1. ‘FLASH’ Characterisation2. Demonstration Experiments3. Future (Path-finding)


Atoms in Intense XUV + Optical (Ti-Sapphire - 800/400 nm) fields

Photoionization of rare gas atoms dressed by intense optical fields

Summary of AMOP@FLASHhttp://hasylab.desy.de/science/user_collaborations/amopflash

Photoionization Experiments with the Ultrafast XUV Laser FLASHJ T Costello, J Phys Conf Ser 88 Art No 012057 (2007)

C. Bostedt et al., Experiments at FLASH, Nucl. Inst. Meth. in Res. A 601 108 (2009)


FLASH NIR/UV and XUV Beam Layout

PG2BL1

BL3

BL2visible laser light


E.S. Toma et al. PRA 62 061801 (2000)

Two colour ATI/ Laser Assisted PES

ElectronSpectrometer

Gas Jet

NIR (800 nm) fs laser pulse

XUV

Superposition of visible and XUV pulses in a noble gas jet

hir =1.55eV

Ar(IP) 15.76 eVSideband intensity very sensitive to XUV-IR pulse area overlap. - Cross Correlation…

Schins et al. PRL 73, 2180 (1994)

LKELKEXUV nTeAnTeAA

M Meyer et al., PRA 69 051401(R) (2004)

Cross (IR-XUV) correlation using HHXUV-IR Cross-Correlation

H19

H17 (26eV)

H21

Ar 3p6

Ar+ 3p5

VUV

IR

e-

15,76 eV

electron kinetic energy /eV

0-20-40-60 20 40 60

Delay / fs

5

10

15

20

Low field regime: Int(IR) ≈ 1011 W/cm2

(sideband)2 = (IR)2 + (VUV)2 T (laser) = 30fs

P. Radcliffe, et al., Nucl. Instr. and Meth. A 83, 516-525 (2007)

Two colour ATI/ Laser Assisted PESExperimental Layout at FLASH - (EU-RTD)

Two colour ATI/ Laser Assisted PES

P. Radcliffe, et al., Nucl. Instr. and Meth. A 83, 516-525 (2007) P. Radcliffe, et al., APL 90 131108 (2007)

Sideband number/intensity depend strongly on XUV/NIR overlap by comparison with theory we are able to determine relative time delay to better than 100 fs

550 fs

1. New ultrafast XUV-modulated optical-reflectivity methods 2. ‘TEO’C. Gahl et al., Nature Photonics 2 165-169 (2008) A. Azima et al., APL.T. Maltezopoulos et al., New J Phys 10 Art. No. 033026 (2008) 94 144102

(2009)

A Maquet and R Taieb, J. Mod. Opt. 54 1847 (2007)

Two colour ATI - ‘Soft Photon’

S n Sin 1 P2 Cos 0

Jn2 0knCos d

d n

d

kk0

Jn2

.K d 0

d

E k

F L

- Classical excursion vector of an electron in a laser field of amplitude

F

One photoncross-section

‘n’ photon ATIcross-section

K

k

k 0 - Momentum transfer

Jn - Bessel function (first kind order ‘n’)

After a little work………….sideband strength is given by an expression like……

kn - Shifted wavenumber of the ejected electron =

2 IP FEL nL - Usual asymmetry parameter

Two colour ATI - Z Scaling

800 nm Ti-Sa1.55 eV/ 120 fs

FLASHh ~ 93 eV20 J/pulse


Low

Resonances !

dCoskJCosPSinS nnn

02

021

Two colour ATI - Z Scaling

FEL Wavelength: 13.9 nmFitted 800 nm intensity~ 5 x 1011 W.cm-2

Intensity ratio of n = SB1/SB2( sidebands) - Model vs Experiment

‘Soft Photon’Experiment


2 colour ATI - FEL Wavelength ScalingFEL + LASER (800 nm)

Sideband Ratios - Comparison of Soft Photon Approximation with Experiment


dCoskJCosPSinS nnn

02

021 LFELIPn nk 2where

2 colour ATI - Optical Intensity ScalingNe: High dressing field sideband distribution

S n Sin 1 P2 Cos 0

Jn2 0knCos d


0 F0

L

2 colour ATI - Optical Intensity ScalingNe: ‘Toy’ SFA Code / Asymmetry in sideband distribution

S n Sin 1 P2 Cos 0

Jn2 0knCos d

Ne: Simulation hFEL = 46 eV


2 IP FEL nL

FLASH: 13.7 nm, 10-20 fs, 20µJOL: 800nm, 4ps, 400µJ, 6 x 1011 W/cm2

He 1s2 + hXUV ----> He+ 1s + pHe 1s2 + hXUV + hOL ---> He+ 1s + s, d

Atomic Dichroism in Two Colour ATIStrong Polarisation Dependence of Sidebands (Low Field)

Meyer et al., PRL 101 Art. no. 193002 (2008)

Atomic Dichroism in Two Colour ATI - HeLow Optical Laser Field High Optical Laser Field

P. Theory: A Grum-Grzhimailo et al. SPA: A Maquet/ R Taieb

Meyer et al., PRL 101 Art. no. 193002 (2008)

SHen Sin Cos2

0

Jn2 0knCos d

d n

d

Jn

2 .

K d 0

d

E k

() = 3Sd + (5Ss + Sd) cos2Ss/Sd =1.25 ± 0.3

Atomic Dichroism in Inner-Shell ATI - KrFLASH: 13.7 nm, 10-20 fs, 20µJOL: 800nm, 4ps, 6 x 1011 W/cm2 SPA works well for both valence

(4p) and inner shell (4s) electrons.


Work in progress to determine s/d ratio from the above…..

Atomic Dichroism in Ionic ATI - Ne+

Ne - Sequential Ionization

‘Work in progress’ - but we can begin to think about studying isonuclear trends…….

UXSS, SLAC - June 18 2009

‘Coherent’ blend of 3P and 1D sidebands….

‘Isolated 3P 1st and 2nd sidebands….

hFEL = 46 eV

1. Ne (2p6 1S) + h (46 eV) Ne+(2p5 2P) + e-(~34 eV)2. Ne+ (2p5 2P) + h (46 eV) Ne2+(2p4 3P/1D) + e-(~ 25 eV)


Atomic Dichroism in Ionic ATI - Ne+

b =0.003

b =0.005

b =0.019

b =0.005

b =0.008

a + b Cos2()

SPA fits in progress…Core ‘2S+1LJ’ effects ?


Two Colour X-ray+NIR Expts @ LSLSCollaboration: J. Bozek, A. Cavalieri, R. Coffee, J. Costello, S. Duesterer, R. Kienberger, M. Meyer, L. DiMauro & T. Tschentscher - LCLS, DESY, MPQ, DCU, Orsay & Ohio

Experimental Plan for Fall 2009 and Proposed for 2010…….

1. Chirped Pulse Laser Assisted Auger Decay - CPLADD

2. Single Shot Atomic Streak Camera - SSASC

Few Femtosecond Photo and Auger Electron Dynamics in Strong Optical Fields

Two Colour X-ray + NIR Expts @ LSLS


Chirped Pulse Laser Assisted Auger Decay - CPLADD

Target: Ne

LCLS: 830-850 eV~50 fs

Laser: 800 nm or650-1100 nm~200 fs

No Chirp1. Auger electron: Linewidth independent of FEL BW (e.g., Ne - 0.23 eV)2. Auger electron pulse mimics LCLS pulse: Electron replica photocathode3. No Chirp: Auger electron bunch exchanges photons with single carrier hL

4. Chirped: Auger bunch exchanges photons with time-varying carrier energy- Ergo different parts of the bunch experience different energy shifts - (time energy) => sideband shapeX-ray pulse profile………

Chirped

Two Colour X-ray+NIR Expts @ LSLS


Single Shot Atomic Streak Camera - SSASCTarget: Rare gas, LCLS: >800 eV, ~1 - 4 fs, Laser: OPA (2000 nm, ~ 7 fs),

1. Electron bunch must replicate ultrashort X-ray pulse…….2. Electron bunch duration must be shorter than one half cycle of the OPA dressing field (~ 3fs)……3. Photoelectron energy shift follows the electric field of the IR dressing laser…..4. In the zero field crossing case the electron pulse is streaked in both directions resulting in a broadened but unshifted electron line - the electron linewidth will depend on the electron (X-ray) bunch length (case ‘b’)5. On the other hand, if the electron bunch falls on the carrier peak, all parts of the bunch ‘feel’ approximately the same dressing field, ergo the electron bunch will be shifted by a constant energy (case ‘c’)6. Postprocessing - retrieve zero crossing cases to determine LCLS pulse width distribution (< 1 to 4 fs ?)

a. Without dressing field =>unshifted, no broadening…..

b. With dressing field (zero crossing) => unshifted, broadened…..

c. With dressing field (peak value) => shifted, no broadening…..

Summary - Two Colour ATI1. Demonstrated interference free SBs to high order,

polarisation control, laser and FEL parameter dependencies & SBs in atomic and ionic targets

2. At low optical intensities 2nd order PT & SPA agree3. Beyond He we really need to measure angular

distributions to try to unravel the ‘l’ channels (Kr 4s ?)4. SPA works well at high intensities but the number of

open high angular momentum channels is a challenge for other approaches such as R-Matrix Floquet (HvdH)

5. Is there really value in going beyond SPA ? Does the residual ion core atomic structure really matter ? (Ne+)

6. LCLS will test the limits of UF X-ray techniques….


Atoms in Intense XUV Fields


Part 3. Few XUV Photon Ionization

FLASH Offers…………


High intensity - 100J/10fs/10m ~ 1016 W/cm2

Expect few photon non-linear photoionization processes…..

Interaction with matter

High (XUV) photon energy - 50 - 200 eV

IP

2Up

UP 9.310 14 I Wcm 2 2 m eV

Keldysh -

where

Atoms in Intense XUV Fields


Keldysh - Ionization RegimeMultiphoton Ionization Tunnel Ionization Field Ionization

>>1 ~ 2 <<1

Intensity/ Wavelength

Photon Energy


I (Units of 1014 W.cm-2) Up (eV)-800 nm Up (eV)-8 nm (800 nm) (8 nm) 0.1 0.59 0.00006 4.50 454 0.5 2.98 0.0003 2.03 203 1 5.95 0.0006 1.44 143 5 29.7 0.003 0.64 64

10 59.5 0.006 0.45 45 100 595.2 0.06 0.14 14

FLASH in the XUV -Pertubative (MPI) Regime:

Ti-Sapphire in the NIRNon-Pertubative (TI) Regime

So these non linear photoionization processes will involvepredominantly few photons and potentially few electrons

Keldysh - Ionization RegimeMultiphoton Ionization Tunnel Ionization Field Ionization

>>1 ~ 2 <<1

Xe ionization in intense XUV fields


Sorokin, Richter et al., PTB, PRL 2008

4d photoionization @ h = 93 eV FEL only. h ~ 93 eV

Xe + h Xe+ + e-

Replace Ion TOF by MBES –photoelectron spectrosopy


Intensityscaling...

Weakestfield…

4d two photon direct ionization FEL only. h ~ 93 eV Xe + 2h Xe+ + e-

Must not ignore 4p- Auger processes also !


Interpretation proving a challenge as ionization and excitation balance changes on a sub-fs timescale (and spatially)…….

Part 4. Next StepsTwo Colour Resonant Photoionization Processes

1. To date we have looked only at one and two colour non-resonant processes

2. Next phase - FEL tunable and so we can explore resonant two colour processes where inner shell electrons dominate


Kr 3d10 4s2 4p6

Kr+ 3d9 2D5/2

4d

XUV46.1 eV

Auger

Kr+ 4p44d, 5d

92.0eV

Experiment. June 15 (2009)

MLM - 3 degree incidence…….

Kr (3d94d) 2 Photon Resonance Auger


Kr: 3d104s24p6 + 2h (46 eV) 3d94s24p64d

1. Kr+: 3d104s24p44d +l (~60 eV)

2. Kr+: 3d104s24p5 + l’ (~75 eV)Kr+ 4p5

Kr 3d10 4s2 4p6

Kr+ 3d9 2D5/2

4d

XUV46.1 eV

Auger

Kr+ 4p44d, 5d

92.0eV

Experiment. June 15 (2009)

MLM - 3 degree incidence…….

Kr (3d94d) 2 Photon Resonance Auger


Kr+ 4p5

FLASH June 18, ca. 5.30 am CETDuesterer, Li & Richardson……

Upgrade at FLASH - Optical Parametric Amplifier - (fs OPA)

Experiments post-upgrade

Laser coupling/spectroscopy of autoionization states


Bachau & Lambropoulos, PRA (1986)Themelis, Lambropoulos, Meyer, JPB (2005)

‘New Knobs’1. Laser Frequency2. Laser Intensity

Tunable Optical Laser - Laser Coupling of autoionization states - 'Autler Townes' Autoionizing Resonances - He

Laser Coupled AutoionisingState Dynamics


FLASH - Technical Developments

OPA Upgrade - 0.01 - 1 mJ/ 0.1 - 20 psSynchronisation - New FIR Undulator (THz)Seeding with HHs - Full coherence

StabilisationSynchroniosation


In Conclusion1. To date we have looked only at one and two colour non-

resonant photoionization processes

2. Now - FEL easily tunable - we can explore resonant two colour processes where inner shell electrons dominate

3. Study fragmentation and ionization from vibrationally excited/selected wavepackets in simple molecules

2. Beyond 2009: FLASH - seeding, fs jitter, angle resolved PES,…X-rays - LCLS/XFEL/SPRING-8/NLS

5. The future is bright and the XUV & X-ray are even more exciting (now) (J-P Connerade, ICL)


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John T. Costello

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