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

What are the Field Applications? Orion. IRAM 30-m telescope line survey Atmospheric Chemistry Astrophysics

Where is the New Excitement? Medical New Physical Regimes Analytical Applications Active and Passive Imaging

Temperature kT (300 K) = 200 cm -1 kT (1.5 K) = 1 cm -1 kT (0.001 K) = cm -1 Fields qE (electron) >> cm -1 mE (1 D) ~ 1 cm -1 mB (electronic) ~ 1 cm -1 mB (nuclear) ~ cm -1 The THz has defined itself broadly and spans kT The Physics - The Energetics Atoms and Molecules E (electronic) ~ 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 cm -1 FIR cm -1 THz cm -1 MW cm -1 RF < 1 cm -1

The ‘Gap’ in the Electromagnetic Spectrum [From Tom Crowe UVA/VDI] Size h /kT Cooling Tubes, a little more - Photomixers, a little less

Blackbody Brightness [W/cm 2 -Hz] Thermal Noise and Power in the THz From E. Brown Number of modes/cm 2 ~ 1/  (cm) Blackbody Noise/mode Thermal Noise below cutoff frequency max in integration bandwidth B Thermal noise in bandwidth b with integration bandwidth B

The THz is VERY Quiet even for CW Systems in Harsh Environments Experiment: SiO vapor at ~1700 K All noise from 1.6 K detector system 1 mW/MHz -> K 1mW/100 Hz -> 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 ~ 10 6 Atmospheric pressure gases: Q ~ 10 2 Solids and Liquids: Q ~ (are there useful signatures?) (are these classical or QM?)

J max  18 J max  30 J max  55 J max  96 J max  305 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 _____________________ 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. h r ~ kT ~ V well

Typical Spectra - HCN

Sources and Metrology for the THz Synthesized Frequency Multiplication

Jumping the THz via Frequency Synthesis Spectroscopy via Photomixing Frequency Reference Spectroscopic Measurement “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, (1972).

VCO Frequency Reference 10.5 GHz Mixer X8 Multiplier W-band W-band Amplifier GHz X3 Multiplier W-band Amplifier Low Pass Filter 10kHz – 1MHz Harmonic 10 MHz Comb Generator Amplifier Mixer Gas CellDetector Computer DAQ Frequency Standard x24 The Multiplied FASSST Spectrometer 10 5 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, (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)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. Ishiguro NMIJ-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, 2005 High-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 Orderdemonstrateddemonstratedclear pathPhenomenaVLP ($spent or $potential) best methodTo be demo Cancer/deep(spectra)X Cancer/surface(spectra)X T-Ray (deep medical)X Mutation(spectra)X Broadband communications ~100 GHz>1 THz Explosives remote with specificityX Classical imagingX Point gas detection absolute specificityX Astrophysics (>$2x10 9 )X Atmospheric (>$n x 10 8 )X Remote gas detection modest specificityX specificity in mixtures at 1km X See through walls~100 GHz>1 THz Buried land mines > 6”~100 GHz> 1THz 1 THz Cancer/surface (water)X Incapacitate and killX Explosives/other solids close, sm obstruct, mixturesX Explosives close, sort, sm obstructsome materials Pharmaceuticals, bio close, sort, sm obstruct some materials

Cost? Size? Speed? Breadth of Application? Impact Orderdemonstrateddemonstratedclear pathPhenomenaVLP ($spent or $potential) best methodTo be demo Cancer/deep(spectra)X Cancer/surface(spectra)X T-Ray (deep medical)X Mutation(spectra)X Broadband communications ~100 GHz>1 THz Explosives remote with specificityX Classical imagingX Point gas detection absolute specificityX Astrophysics (>$2x10 9 )X Atmospheric (>$n x 10 8 )X Remote gas detection modest specificityX See through walls~100 GHz>1 THz Buried land mines > 6”~100 GHz> 1THz 1 THz Cancer/surface (water)X Incapacitate and killX Explosives/other solids close, sm obstruct, mixturesX Explosives close, sort, sm obstructsome materials Pharmaceuticals, bio close, sort, sm obstruct some materials Legacy Applications

Impact Orderdemonstrateddemonstratedclear pathPhenomenaVLP ($spent or $potential) best methodTo be demo Cancer/deep(spectra)X Cancer/surface(spectra)X T-Ray (deep medical) Mutation(spectra)X Broadband communications ~100 GHz>1 THz Explosives remote with specificity Classical imagingX Remote gas detectionX modest specificity Astrophysics (>$2x10 9 )X Atmospheric (>$n x 10 8 )X See through walls~100 GHz>1 THz Point gas detection absolute specificityX Buried land mines > 6”~100 GHz> 1THz 1 THz Cancer/surface (water)X Incapacitate and killX Explosives/other solids close, sm obstruct, mixturesX Explosives close, sort, sm obstructsome materials Pharmaceuticals, bio close, sort, sm obstruct some materials

Impact Orderdemonstrateddemonstratedclear pathPhenomenaVLP ($spent or $potential) best methodto be demo Cancer/deep(spectra)X Cancer/surface(spectra)X T-Ray (deep medical)X Mutation(spectra)X Broadband communications ~100 GHz>1 THz Explosives remote with specificityX Classical imagingX Remote gas detection modest specificityX Point gas detection absolute specificityX Astrophysics (>$2x10 9 )X Atmospheric (>$n x 10 8 )X See through walls~100 GHz>1 THz Buried land mines > 6”~100 GHz> 1THz 1 THz Cancer/surface (water)X Incapacitate and killX Explosives/other solids close, sm obstruct, mixturesX Explosives close, sort, sm obstruct some materials Pharmaceuticals, bio close, sort, sm obstructsome 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” e 20 attenuation in 1 mm

Impact Orderdemonstrateddemonstratedclear pathPhenomenaVLP ($spent or $potential) best methodTo be demo Cancer/deep(spectra)X Cancer/surface(spectra)X T-Ray (deep medical) Mutation(spectra)X Broadband communications ~100 GHz>1 THz Explosives remote with specificityX Astrophysics (>$2x10 9 )X Atmospheric (>$n x 10 8 )X Classical imagingT&S Remote gas detection modest specificityT&S See through walls~100 GHz>1 THz Point gas detection absolute specificityX Buried land mines > 6”~100 GHz> 1THz 1 THz Cancer/surface (water)X Incapacitate and killX Explosives close, sort, sm obstructsome materials Pharmaceuticals, 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 Orderdemonstrateddemonstratedclear pathPhenomenaVLP ($spent or $potential) best methodTo be demo Cancer/deep(spectra)X Cancer/surface(spectra)X T-Ray (deep medical) Mutation(spectra)X Broadband communications ~100 GHz>1 THz Explosives remote with specificityX Astrophysics (>$2x10 9 )X Atmospheric (>$n x 10 8 )X Classical imagingT&S Remote gas detection modest specificityT&S See through walls~100 GHz>1 THz Point gas detection absolute specificityX Buried land mines > 6”~100 GHz> 1THz 1 THz Cancer/surface (water)X Incapacitate and killX Explosives/other solids close, sm obstruct, mixturesX Explosives close, sort, sm obstructsome materials Pharmaceuticals, 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 => 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