Terahertz Spectroscopy and Applications
Frank C. De LuciaDepartment of PhysicsOhio State University
IEEE International Frequency Control SymposiumJune 5 - 7, 2006 Miami, Florida
PEOPLE
Doug Petkie - Professor WSUEric Herbst - Professor OSU
Brenda Winnewisser - Adj. Professor OSUManfred Winnewisser - Adj. Professor OSU
Paul Helminger - Professor USAAtsuko Maeda - Research AssociateIvan Medvedev - Research AssociateAndrei Meshkov - Graduate StudentTJ Ronningen - Graduate Student
Laszlo Sarkozy - Graduate StudentDavid Graff - Graduate StudentCory Casto - Graduate Student
Kerra Fletcher - Graduate StudentBryan Hern - Undergraduate Student
Drew Steigerwald - Undergraduate StudentJohn Hoftiezer - Electrical Engineer
The Lay of the Land
What is the basic physics of the SMM/THz?
How does this impact technology and frequency control?
What physics does it lead us to naturally - What are the important applications?
Where is the excitement?
What is the Physics of the SMM/THz? The Energetics: h ≤ kT
The Classical Size Scale ≤ 1 mm
Noise
Interactions: Gases, Liquids, and Solids
Atmospheric Absorption
Classical Scattering and Penetration
Technology and Frequency Control
Solid-State THz Sources (CW)
0.001
0.01
0.1
1
10
100
1000
10000
10 100 1,000 10,000 100,000
Frequency (GHz)
Po
wer
(mW
)
What are the Field Applications?
Orion. IRAM 30-m telescope line survey
Atmospheric Chemistry
Astrophysics
Where is the New Excitement?
4 0 0
3 0 0
2 0 0
1 0 0
0
- 1 0 0
3 3 3 .1 03 3 3 .0 83 3 3 .0 63 3 3 .0 43 3 3 .0 23 3 3 .0 0x 1 0
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3 0 0 0
2 0 0 0
1 0 0 0
0
- 1 0 0 0
3 7 0 x 1 03
3 6 03 5 03 4 03 3 0F re q u e n c y ( M H z )
4 0 0
2 0 0
0
-2 0 0
3 3 3 .1 0 x1 03
3 3 3 .0 83 3 3 .0 63 3 3 .0 43 3 3 .0 23 3 3 .0 0Frequency (MHz)
#09 Acrylontrile Library
Combined Spectrum
Medical
New Physical RegimesAnalytical Applications
Active and Passive Imaging
Temperature
kT (300 K) = 200 cm-1
kT (1.5 K) = 1 cm-1
kT (0.001 K) = 0.0007 cm-1
Fields
qE (electron) >> 100000 cm-1
mE (1 D) ~ 1 cm-1
mB (electronic) ~ 1 cm-1
mB (nuclear) ~ 0.001 cm-1
The THz has defined itself broadly and spans kT
The Physics - The EnergeticsAtoms and Molecules
E (electronic) ~ 50000 cm-1
E (vibrational) ~ 1000 cm-1
E (rotational) ~ 10 cm-1
E (fine structure) ~ 0.01 cm-1
Radiation
UV/Vis > 3000 cm-1
IR 300 - 3000 cm-1
FIR 30 - 300 cm-1
THz 3 - 300 cm-1
MW 1 - 10 cm-1
RF < 1 cm-1
The ‘Gap’ in the Electromagnetic Spectrum
Solid-State THz Sources (CW)
0.001
0.01
0.1
1
10
100
1000
10000
10 100 1,000 10,000 100,000
Frequency (GHz)
Po
wer
(mW
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[From Tom Crowe UVA/VDI]
Size
h/kT
Cooling
Tubes, a little more - Photomixers, a little less
PN ~ kT (Bmax )1
2 ~ kTmax
B
max
12
Blackbody Brightness [W/cm2-Hz]
Thermal Noise and Power in the THz
From E. Brown
Number of modes/cm2 ~ 1/(cm)
Blackbody Noise/mode
Thermal Noise below cutoff frequency max in integration bandwidth B
Thermal noise in bandwidth b with integration bandwidth B
PN kTb
PN kT (bB)1/2
The THz is VERY Quiet even for CW Systems in Harsh Environments
QuickTime™ and a Photo - JPEG decompressor are needed to see this picture.
Experiment: SiO vapor at ~1700 K
All noise from 1.6 K detector system
1 mW/MHz -> 1014 K
1mW/100 Hz -> 1018 K
“Noise, detectors, and submillimeter-terahertz system performance in nonambient environments”
Frank C. De Lucia
J. Opt. Soc. B, 1275 (2004)
What is the Physics of Interactions?
Separate into Three Classes by Linewidth
Low pressure gases: Q ~ 106
Atmospheric pressure gases: Q ~ 102
Solids and Liquids: Q ~ 1 - 100
(are there useful signatures?)
(are these classical or QM?)
GHzCBA 25 Jmax 18
GHzCBA 10 Jmax 30
GHzCBA 3 Jmax 55
GHzCBA 1 Jmax 96
GHzCBA 1.0 Jmax 305
inertia of moment
1~constant Rotational
Spectra as a Function of Molecular Size
Population of levels
Atmospheric Propagation
Collisional Cooling: An Approach to Gas Phase Studies at Low Temperature
Atom Envy - Molecule Envy
Quantum Collisions
300 K 1 K_____________________
L ~ 30J ~ 10
L ~ 2J 1
Correspondence Principle
The predictions of the quantum theory for the behavior of any physical system must correspond to the prediction of classical physics in the limit in which the quantum numbers specifying the state of the system become very large.
hr ~ kT ~ Vwell
Typical Spectra - HCN
Sources and Metrology for the THzSynthesized Frequency Multiplication
Jumping the THz via Frequency SynthesisSpectroscopy via Photomixing
Fre
qu
ency
Ref
eren
ce
Sp
ectr
osc
op
ic M
easu
rem
ent
“Speed of Light from Direct Frequency and Wavelength Measurements of the Methane-Stabilized Laser,”
K. M. Evenson, J. S. Wells, F. R. Petersen, B. L. Danielson, G. W. Lay, R. L. Barger, and J. L. Hall,
Phys. Rev. Lett. 29, 1346-1349 (1972).
VCO FrequencyReference10.5 GHz
Mixer
X8 MultiplierW-band
W-band Amplifier75-110 GHz
X3 MultiplierW-band
AmplifierLow Pass Filter10kHz – 1MHz
Harmonic10 MHz Comb
GeneratorAmplifierMixer
Gas Cell Detector
Computer DAQ
FrequencyStandard
x24
The Multiplied FASSST Spectrometer
105 resolution elements/sec
The Fundamental FASSST Spectrometer
“Frequency and phase-lock control of a 3 THz quantum cascade laser.”
A. L. Betz, R. T. Boreiko, B. S. Williams, S. Kumar, Q. Hu, J. L. Reno.
Opt Lett. 30, 1837-9 (2005).
Frequency Control and Reference in the THz
“A Tunable Cavity-Locked Diode Laser Source for Terahertz Photomixing,”
S. Matsuura, P. Chen, G. A. Blake, J. C. Pearson, and H. M. Pickett,
IEEE Trans. Microwave Theory and Tech. 48, 380 (2000).
Frequency Synthesis via Femtosecond Demodulation
“Microwave generation from picosecond demodulation sources”
F. C. De Lucia, B. D. Guenther, and T. Anderson
Appl. Phys. Lett. 47, 894 (1985)
I(f)
f “Spectral Purity and Sources of Noise in Femtosecond-Demodulation Terahertz Sources Drive by Ti:Sapphire Mode-Locked Lasers”
J. R. Demers, T. M. Goyette, Kyle B. Ferrio, H. O. Everitt, B. D. Guenther, and F. C. De Lucia
IEEE J. Quant. Electron. 37, (2004).
“Optical frequency synthesis based on mode-locked lasers”
S. T. Cundiff, J. Ye, and J. L. Hall
Rev. Sci. Instrum. 72, 3749 (2001)
THz Synthesis from the Optical Comb
As with Evenson, THz mixer bandwidth and efficiency highly desirable
Atmospheric Remote Sensing
JPL - Microwave Limb Sounder
Ozone Destruction
Cycle
Microwave Limb Sounder
Image courtesy of NRAO/AUI and Computer graphics by ESO
“Generation and Distribution of the mm-wave Reference Signal for ALMA”M. Musha, Y. Sato, K. Nakagawa, K. Ueda, A. Ueda, and M. IshiguroNMIJ-BIPM Workshop, Tsukuba 2004
Orion. IRAM 30-m telescope line survey
“Whispered Excitement about the THz”
Graham Jordan Opening Plenary Presentation SPIE Symposium: Optics/Photonics in Security and Defense Bruges, Belgium, 26 September, 2005
‘New’ Applications - Holy Grails
How do we Move Beyond
to
A Field with many ‘Public’ Applications?
The New York Times - July 11, 2005High-Tech Antiterror Tools: A Costly,
Long-Range Goal
Millimeter wave machines . . .use trace amounts of heat released by objects . . .to create images that can identify hidden bombs . . . from about 30 feet away.
Terahertz radiation devices can create images of concealed objects as well as identify the elemental components of a hidden item.
The terahertz devices may be more promising since they could sound an alarm if someone entering a subway or train station had traces of elements used in bombs on them.
Resolution
Spectroscopic Identification
Penetration
Impact Order demonstrated demonstrated clear path PhenomenaVLP
($spent or $potential) best method To be demo
Cancer/deep(spectra) XCancer/surface(spectra) XT-Ray (deep medical) XMutation(spectra) XBroadband communications ~100 GHz >1 THzExplosives remote with specificity XClassical imaging XPoint gas detection
absolute specificity XAstrophysics (>$2x109) XAtmospheric (>$n x 108) XRemote gas detection
modest specificity X specificity in mixtures at 1km X
See through walls ~100 GHz >1 THz
Buried land mines> 6” ~100 GHz > 1THz< 6” >1 THz
Cancer/surface (water) XIncapacitate and kill XExplosives/other solids close, sm obstruct, mixtures XExplosives close, sort, sm obstruct some materialsPharmaceuticals, bio close, sort, sm obstruct some materials
Cost? Size? Speed?
Breadth of Application?
Impact Order demonstrated demonstrated clear path PhenomenaVLP
($spent or $potential) best method To be demo
Cancer/deep(spectra) XCancer/surface(spectra) XT-Ray (deep medical) XMutation(spectra) XBroadband communications ~100 GHz >1 THzExplosives remote with specificity XClassical imaging XPoint gas detection
absolute specificity XAstrophysics (>$2x109) XAtmospheric (>$n x 108) XRemote gas detection
modest specificity XSee through walls ~100 GHz >1
THzBuried land mines
> 6” ~100 GHz > 1THz< 6” >1 THz
Cancer/surface (water) XIncapacitate and kill XExplosives/other solids close, sm obstruct, mixtures XExplosives close, sort, sm obstruct some materialsPharmaceuticals, bio close, sort, sm obstruct some materials
Legacy Applications
Impact Order demonstrated demonstrated clear path PhenomenaVLP
($spent or $potential) best method To be demo
Cancer/deep(spectra) XCancer/surface(spectra) XT-Ray (deep medical)Mutation(spectra) XBroadband communications ~100 GHz >1 THzExplosives remote with specificityClassical imaging XRemote gas detection X
modest specificityAstrophysics (>$2x109) XAtmospheric (>$n x 108) XSee through walls ~100 GHz >1
THzPoint gas detection
absolute specificity XBuried land mines
> 6” ~100 GHz > 1THz< 6” >1 THz
Cancer/surface (water) XIncapacitate and kill XExplosives/other solids close, sm obstruct, mixtures XExplosives close, sort, sm obstruct some materialsPharmaceuticals, bio close, sort, sm obstruct some materials
Impact Order demonstrated demonstrated clear path PhenomenaVLP
($spent or $potential) best method to be demo
Cancer/deep(spectra) XCancer/surface(spectra) XT-Ray (deep medical) XMutation(spectra) XBroadband communications ~100 GHz >1 THzExplosives remote with specificity XClassical imaging XRemote gas detection
modest specificity XPoint gas detection
absolute specificity XAstrophysics (>$2x109) XAtmospheric (>$n x 108) XSee through walls ~100 GHz >1
THzBuried land mines
> 6” ~100 GHz > 1THz< 6” >1 THz
Cancer/surface (water) XIncapacitate and kill XExplosives/other solids close, sm obstruct, mixtures XExplosives close, sort, sm obstruct some materialsPharmaceuticals, bio close, sort, sm obstruct some materials
“it could be used to scan for diseases, such as cancer, the cells of which have a vibrant terahertz signature.”“New-wave body imaging -
medical imaging using Terahertz radiation”
e20 attenuation in 1 mm
Impact Order demonstrated demonstrated clear path PhenomenaVLP
($spent or $potential) best method To be demo
Cancer/deep(spectra) XCancer/surface(spectra) XT-Ray (deep medical)Mutation(spectra) XBroadband communications ~100 GHz >1 THzExplosives remote with specificity XAstrophysics (>$2x109) XAtmospheric (>$n x 108) XClassical imaging T&SRemote gas detection
modest specificity T&SSee through walls ~100 GHz >1
THzPoint gas detection
absolute specificity XBuried land mines
> 6” ~100 GHz > 1THz< 6” >1 THz
Cancer/surface (water) XIncapacitate and kill X
Explosives close, sort, sm obstruct some materialsPharmaceuticals, bio close, sort, sm obstruct some materials
“A camera that can see through clothes, skin and even walls without X-rays has been developed in what is being called one of the first great technological breakthroughs of the 21st century”
Impact Order demonstrated demonstrated clear path PhenomenaVLP
($spent or $potential) best method To be demo
Cancer/deep(spectra) XCancer/surface(spectra) XT-Ray (deep medical)Mutation(spectra) XBroadband communications ~100 GHz >1 THzExplosives remote with specificity XAstrophysics (>$2x109) XAtmospheric (>$n x 108) XClassical imaging T&SRemote gas detection
modest specificity T&SSee through walls ~100 GHz >1
THzPoint gas detection
absolute specificity XBuried land mines
> 6” ~100 GHz > 1THz< 6” >1 THz
Cancer/surface (water) XIncapacitate and kill XExplosives/other solids close, sm obstruct, mixtures XExplosives close, sort, sm obstruct some materialsPharmaceuticals, bio close, sort, sm obstruct some materials
“Since cancerous tissue tends to have a higher water content than healthy tissue, terahertz radiation could be used to differentiate between the two.”
?
A Good Challenge
Signatures: Explosives Spectra
Clearly spurious results in both gas and
solids have been reported
How do you look at THz images?
What is so favorable about the SMM/THz?What are the Opportunities?
The SMM/THz combines penetrability with -a reasonable diffraction limit -a spectroscopic capability -low pressure gases have strong, redundant, unique signatures
-solids can have low lying vibrational modes, especially at high THz frequencies
Rotational transition strengths peak in the SMM/THz
The SMM/THz is very quiet: 1 mW/MHz => 1014 K
The commercial wireless market will provide us with a cheap technology
It should be possible to engineer small (because of the short wavelength), high spectral purity (because we can derive via multiplication from rf reference) and low power (because the background is quiet/the quanta is small) devices and systems
What is so Challenging about the SMM/THz?
Efficient generation of significant tunable, spectrally pure power levels
Practical broadband frequency control and measurement
The need to develop systems without knowledge of the phenomenology
Impact of the atmosphere