Terahertz Spectroscopy and Applications Frank C. De Lucia

Terahertz Spectroscopy and Applications Frank C. De Lucia

Terahertz Spectroscopy and Applications Frank C. De Lucia Department of Physics Ohio State University IEEE International Frequency Control Symposium June 5 - 7, 2006 Miami, Florida PEOPLE Doug Petkie - Professor WSU Eric Herbst - Professor OSU Brenda Winnewisser - Adj. Professor OSU Manfred Winnewisser - Adj. Professor OSU Paul Helminger - Professor USA Atsuko Maeda - Research Associate Ivan Medvedev - Research Associate Andrei Meshkov - Graduate Student TJ Ronningen - Graduate Student Laszlo Sarkozy - Graduate Student David Graff - Graduate Student

Cory Casto - Graduate Student Kerra Fletcher - Graduate Student Bryan Hern - Undergraduate Student Drew Steigerwald - Undergraduate Student John 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 Source s (CW) 10000 P o w er (m W ) 1000 100 10 1 0.1 0.01 0.001 10 100 1,000 Frequency (GHz) 10,000 100,000

What are the Field Applications? Atmospheric Chemistry Astrophysics Orion. IRAM 30-m telescope line survey Where is the New Excitement? Analytical Applications New Physical Regimes 3 0 0 0 2 0 0 0 1 0 0 0 0 -1 0 0 0 3 3 0

3 4 0 3 5 0 F re q u e n c y ( M H z ) 3 3 6 0 3 7 0 x 1 0 40 0 #09 Acrylontrile Library 30 0 20 0 10 0 0

-1 0 0 3 3 3 .0 0 3 3 3 .0 2 3 3 3 .0 4 3 3 3 3 .0 6 3 3 3 .0 8 3 3 3 .1 0 3 3 3 .0 8 3 3 3 . 1 0 x1 0 x1 0

400 Combined Spectrum 200 0 -2 0 0 3 3 3 .0 0 3 3 3 .0 2 3 3 3 .0 4 3 3 3 .0 6 3 Frequ enc y ( MH z ) Medical

Active and Passive Imaging The Physics - The Energetics 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 Atoms 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 mE (1 D) ~ 1 cm-1

UV/Vis > 3000 cm-1 mB (electronic) ~ 1 cm-1 IR 300 - 3000 cm-1 mB (nuclear) ~ 0.001 cm-1 FIR 30 - 300 cm-1 THz 3 - 300 cm-1 The THz has defined itself broadly and spans kT MW 1 - 10 cm-1 RF < 1 cm-1 The Gap in the Electromagnetic Spectrum Solid-State THz Sources (CW) Tubes, a little more - Photomixers, a little less 10000

P o w er (m W ) 1000 h/kT 100 Size 10 1 Cooling 0.1 0.01 0.001 10 100 1,000

10,000 100,000 Frequency (GHz) [From Tom Crowe UVA/VDI] Thermal Noise and Power in the THz Blackbody Brightness Blackbody Noise/mode [W/cm2-Hz] Thermal Noise below cutoff frequency max in integration bandwidth B PN kTb PN ~ kT (B max ) 1

2 Thermal noise in bandwidth b with integration bandwidth B PN kT (bB)1/ 2 From E. Brown Number of modes/cm2 ~ 1/(cm) 1 B 2 ~ kT max max

The THz is VERY Quiet even for CW Systems in Harsh Environments Experiment: SiO vapor at ~1700 K QuickTime and a Photo - JPEG decompressor are needed to see this picture. All noise from 1.6 K detector system Noise, detectors, and submillimeter-terahertz system performance in nonambient environments Frank C. De Lucia J. Opt. Soc. B, 1275 (2004) 1 mW/MHz -> 1014 K 1mW/100 Hz -> 1018 K 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?) Spectra as a Function of Molecular Size Rotational constant ~ 1 moment of inertia Population of levels A B C 25 GHz Jmax 18 A B C 10 GHz Jmax 30 A B C 3 GHz Jmax 55

A B C 1 GHz Jmax 96 A B C 0.1 GHz Jmax 305 Atmospheric Propagation Collisional Cooling: An Approach to Gas Phase Studies at Low Temperature Atom Envy - Molecule Envy Quantum Collisions 300 K 1K _____________________ L ~ 30

L ~ 2 J ~ 10 J 1 h ~ V ~ kT r well 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. Typical Spectra - HCN Sources and Metrology for the THz Synthesized Frequency Multiplication Jumping the THz via Frequency Synthesis 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). Spectroscopic Measurement Speed of Light from Direct Frequency and Wavelength Measurements of the MethaneStabilized Laser, Frequency Reference Spectroscopy via Photomixing

The Multiplied FASSST Spectrometer VCO Mixer X8 Multiplier W-band W-band Amplifier 75-110 GHz Mixer x24 Amplifier Frequency Standard Harmonic 10 MHz Comb

Generator Amplifier Low Pass Filter 10kHz 1MHz X3 Multiplier W-band Gas Cell Frequency Reference 10.5 GHz Computer DAQ Detector 105 resolution elements/sec The Fundamental FASSST Spectrometer 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 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 Synthesis via Femtosecond Demodulation I(f) f Microwave generation from picosecond demodulation sources F. C. De Lucia, B. D. Guenther, and T. Anderson Appl. Phys. Lett. 47, 894 (1985) 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). THz Synthesis from the Optical Comb Optical frequency synthesis based on mode-locked lasers S. T. Cundiff, J. Ye, and J. L. Hall 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. Ishiguro NMIJ-BIPM Workshop, Tsukuba 2004 Orion. IRAM 30-m telescope line survey New Applications - Holy Grails How do we Move Beyond Whispered Excitement about the THz Graham Jordan Opening Plenary Presentation SPIE Symposium: Optics/Photonics in Security and Defense Bruges, Belgium, 26 September, 2005 to

A Field with many Public Applications? The New York Times - July 11, 2005 High-Tech Antiterror Tools: A Costly, Long-Range Goal Resolution 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.

Penetration Spectroscopic Identification Impact Order ($spent or $potential) Cancer/deep(spectra) Cancer/surface(spectra) T-Ray (deep medical) Mutation(spectra) Broadband communications Explosives remote with specificity Classical imaging Point gas detection absolute specificity Astrophysics (>$2x109) Atmospheric (>$n x 108) Remote gas detection modest specificity specificity in mixtures at 1km See through walls

Buried land mines > 6 < 6 Cancer/surface (water) Incapacitate and kill Explosives/other solids close, sm obstruct, mixtures Explosives close, sort, sm obstruct Pharmaceuticals, bio close, sort, sm obstruct demonstrated best method demonstrated clear path Phenomena To be demo VLP

X X X X ~100 GHz >1 THz X X X X X X X ~100 GHz ~100 GHz >1 THz X >1 THz > 1THz

X X some materials some materials Impact Order ($spent or $potential) demonstrated best method demonstrated Cancer/deep(spectra) Cancer/surface(spectra) T-Ray (deep medical) Mutation(spectra) Legacy Applications Broadband communications ~100 GHz Explosives remote with specificity

Classical imaging Cost? Size? Speed? Point gas detection Breadth of Application? absolute specificity Astrophysics (>$2x109) X 8 Atmospheric (>$n x 10 ) X Remote gas detection modest specificity See through walls Buried land mines > 6 < 6 Cancer/surface (water) Incapacitate and kill Explosives/other solids close, sm obstruct, mixtures Explosives close, sort, sm obstruct some materials

Pharmaceuticals, bio close, sort, sm obstruct some materials clear path Phenomena To be demo VLP X X X X >1 THz X X X X ~100 GHz ~100 GHz

>1 THz X >1 THz > 1THz X X Impact Order ($spent or $potential) Cancer/deep(spectra) Cancer/surface(spectra) T-Ray (deep medical) Mutation(spectra) Broadband communications Explosives remote with specificity Classical imaging Remote gas detection modest specificity Astrophysics (>$2x109) Atmospheric (>$n x 108)

See through walls Point gas detection absolute specificity Buried land mines > 6 < 6 Cancer/surface (water) Incapacitate and kill Explosives/other solids close, sm obstruct, mixtures Explosives close, sort, sm obstruct Pharmaceuticals, bio close, sort, sm obstruct demonstrated best method demonstrated clear path Phenomena

To be demo VLP X X X ~100 GHz >1 THz X X X X ~100 GHz >1 THz X ~100 GHz >1 THz X

> 1THz X X some materials some materials Impact Order ($spent or $potential) demonstrated best method demonstrated clear path it could be used to scan for diseases, such as Cancer/deep(spectra) cancer, the cells of which have a vibrant terahertz Cancer/surface(spectra) signature.

New-wave body imaging T-Ray (deep medical) medical imaging using Terahertz Mutation(spectra) Broadband communications ~100 GHz >1 THz radiation Explosives remote with specificity e20 attenuation Classical imaging X in 1 mm Remote gas detection modest specificity X Point gas detection absolute specificity X Astrophysics (>$2x109) X Atmospheric (>$n x 108)

X See through walls Buried land mines > 6 ~100 GHz < 6 Cancer/surface (water) X Incapacitate and kill Explosives/other solids close, sm obstruct, mixtures Explosives close, sort, sm obstruct some materials Pharmaceuticals, bio close, sort, sm obstruct some materials Phenomena to be demo VLP X

X X X X ~100 GHz >1 THz > 1THz >1 THz X X Impact Order ($spent or $potential) demonstrated best method demonstrated

Cancer/deep(spectra) Cancer/surface(spectra) T-Ray (deep medical) Mutation(spectra) Broadband communicationsA camera ~100 GHzsee through clothes, skin that can Explosives and even walls without X-rays has been remote with specificity developed in what is being called one of the Astrophysics (>$2x109) first great Xtechnological breakthroughs of the 8 Atmospheric (>$n x 10 ) X 21st century Classical imaging Remote gas detection modest specificity See through walls Point gas detection absolute specificity X

Buried land mines > 6 < 6 Cancer/surface (water) X Incapacitate and kill Explosives close, sort, sm obstruct Pharmaceuticals, bio close, sort, sm obstruct some materials some materials clear path Phenomena To be demo VLP X X

X >1 THz X T&S T&S ~100 GHz ~100 GHz >1 THz >1 THz > 1THz X Impact Order ($spent or $potential) demonstrated best method demonstrated

Cancer/deep(spectra) Cancer/surface(spectra) T-Ray (deep medical) Mutation(spectra) Broadband communications ~100 GHz Explosives remote with specificity Astrophysics (>$2x109) X 8 Atmospheric (>$n x 10 ) X Classical imaging Remote gas detection modest specificity Since cancerous tissue tends to have a higher See through walls water content than healthy tissue, terahertz Point gas detection radiation could be used to differentiate between absolute specificity

X the two. Buried land mines > 6 < 6 Cancer/surface (water) X ? Incapacitate and kill Explosives/other solids close, sm obstruct, mixtures Explosives close, sort, sm obstruct some materials Pharmaceuticals, bio close, sort, sm obstruct some materials A Good Challenge clear path Phenomena

To be demo VLP X X X >1 THz X T&S T&S ~100 GHz ~100 GHz >1 THz >1 THz > 1THz X X 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

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