Terahertz Signature Science: The Second Gap in the Electromagnetic Spectrum Frank C. De Lucia

1. Penetration Resolution Spectroscopic Identification Terahertz Signature Science: The Second Gap in the Electromagnetic Spectrum Frank C. De Lucia Department of Physics Ohio State University International Symposium on Spectral Sensing Research Bar Harbor, Maine June 1, 2006 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. CONCEPTS ARE NICE BUT THE NUMBERS MATTER

2. From Mark Rosker The Beginning Theses: No ‘Public’ THz application has yet come to fruition - Why? What do we need to do to remedy this? 1. We need ‘End-to-End’ systems analyses for the most widely discussed applications. 2. We need to consider appropriate figures of merit for the several technical approaches and choose the technology best suited for the application. 3. Often a lot more is known about the signatures and phenomenology than we consider as we propose applications. (this leads to proposed applications which threaten our credibility) 4. But in other cases the phenomenology and signature science is only poorly know. (this leads to missed opportunities)

3. Two SMM/THz Legacy ‘Public’ Applications -- Clear, but Challenging Paths to Success -- IMAGING ANALYTICAL CHEMISTRY Technical and Scientific R & D Impact The Breadth of Applicability

4. Why is there a ‘Clear Path’ to Imaging? Many special purpose imagers have been built over the last 40+ years Detectors - scientifically we understand - in single element receivers we can approach well understood fundamental limits Transmit power - acceptable solid state sources for some applications exist Propagation -overall absorption generally known -impact of fluctuations noise less clear Recognition/targets/clutter -preliminary studies completed -nature of active images complex, but large contrast in images provides opportunities -TIFT can start to do realistic end to end calculations Where can we get to on sensitivity-speed-size-cost tradeoff? Quantitatively, what are the target signatures, clutter, and phenomenology for scenarios of interest? These are not show stoppers, but the answers will determine the Breath of Application

5. Why is there a ‘Clear Path’ to Analytical Chemistry? A well understood spectroscopic foundation is in place False alarm rates in complex environments have been studied and can be shown to be low because of the number of resolution elements and ‘complex redundancy’ of molecular fingerprints Background clutter/interference at trace levels have been studied and can be shown to be low What we need to know/develop Trade-offs among size, cost, sensitivity, power consumption Speed of cost reduction from mass wireless market? Development of a signature science for larger molecules These are not show stoppers, but the answers will determine the Breath of Application

6. Quantitative end-to-end designs

7. Parallel and On Going MM/SMM Science [Field Technology and Systems Grew out of Lab Science] NASA JPL catalog HITRAN, KOLN, GEISA data bases Ongoing Data Base Development ALMA - Denmark HITRAN NASA The GEISA/IASI spectroscopic database

8. Applications Matrix as introduction to Signature Science

9. Impact Order demonstrated demonstrated clear path Phenomena VLP ($spent or $potential) best method To 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 specificity X Classical imaging X Point gas detection absolute specificity X Astrophysics (>$2x109) X Atmospheric (>$n x 108) X Remote 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) X Incapacitate and kill X Explosives/other solids close, sm obstruct, mixtures X Explosives close, sort, sm obstruct some materials Pharmaceuticals, bio close, sort, sm obstruct some materials

10. Impact Order demonstrated demonstrated clear path Phenomena VLP ($spent or $potential) best method To 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 specificity X Classical imaging X Point gas detection absolute specificity X Astrophysics (>$2x109) X Atmospheric (>$n x 108) X Remote gas detection modest specificity X See through walls ~100 GHz >1 THz Buried land mines > 6” ~100 GHz > 1THz < 6” >1 THz Cancer/surface (water) X Incapacitate and kill X Explosives/other solids close, sm obstruct, mixtures X Explosives close, sort, sm obstruct some materials Pharmaceuticals, bio close, sort, sm obstruct some materials Legacy Applications Cost? Size? Speed? Breadth of Application?

11. Impact Order demonstrated demonstrated clear path Phenomena VLP ($spent or $potential) best method To 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 imaging X Remote gas detection X modest specificity Astrophysics (>$2x109) X Atmospheric (>$n x 108) X See through walls ~100 GHz >1 THz Point gas detection absolute specificity X Buried land mines > 6” ~100 GHz > 1THz < 6” >1 THz Cancer/surface (water) X Incapacitate and kill X Explosives/other solids close, sm obstruct, mixtures X Explosives close, sort, sm obstruct some materials Pharmaceuticals, bio close, sort, sm obstruct some materials

12. “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 Phenomena VLP ($spent or $potential) best method to 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 specificity X Classical imaging X Remote gas detection modest specificity X Point gas detection absolute specificity X Astrophysics (>$2x109) X Atmospheric (>$n x 108) X See through walls ~100 GHz >1 THz Buried land mines > 6” ~100 GHz > 1THz < 6” >1 THz Cancer/surface (water) X Incapacitate and kill X Explosives/other solids close, sm obstruct, mixtures X Explosives close, sort, sm obstruct some materials Pharmaceuticals, bio close, sort, sm obstruct some materials

13. “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 Phenomena VLP ($spent or $potential) best method To 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 X Astrophysics (>$2x109) X Atmospheric (>$n x 108) X Classical imaging T&S Remote gas detection modest specificity T&S See through walls ~100 GHz >1 THz Point gas detection absolute specificity X Buried land mines > 6” ~100 GHz > 1THz < 6” >1 THz Cancer/surface (water) X Incapacitate and kill X Explosives close, sort, sm obstruct some materials Pharmaceuticals, bio close, sort, sm obstruct some materials

14. “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 Impact Order demonstrated demonstrated clear path Phenomena VLP ($spent or $potential) best method To 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 X Astrophysics (>$2x109) X Atmospheric (>$n x 108) X Classical imaging T&S Remote gas detection modest specificity T&S See through walls ~100 GHz >1 THz Point gas detection absolute specificity X Buried land mines > 6” ~100 GHz > 1THz < 6” >1 THz Cancer/surface (water) X Incapacitate and kill X Explosives/other solids close, sm obstruct, mixtures X Explosives close, sort, sm obstruct some materials Pharmaceuticals, bio close, sort, sm obstruct some materials ?

15. Signatures: Explosives Spectra Clearly spurious results in both gas and solids have been reported

16. From THz-Bridge Are any of us willing to say that we are sure that the sharp lines are spurious? The solid line shows the reflectivity of the meat part normalized of the reflectivity of the fat part of Black Forrest ham averaged on three points each.

17. Clutter and Noise in the SMM/THz

18. The THz is VERY Quiet even for CW Systems in Harsh Environments Experiment: SiO vapor at ~1700 K Good News - CW systems are ~1010 better than has been widely claimed All noise from 1.6 K detector system

19. Impact of Atmospheric Transmission on Spectral Fingerprints - What’s a THz? Signature, with perfect atmo model

20. Signatures vs Pictures: Humans at 650 GHz Active Image Skin is close to specular - Hair really lights up At least 40 db of dynamic range across this target A high contrast target signature is very good for recognition if you have system sensitivity to observe Thermal Image: DT/T = 0.1

21. Clutter Limits in Imaging Temporal and Spatial Scales When do we reach clutter limits as a function of frequency?

23. Systems: Remote Spectroscopic Sensing Gas Phase Example: 100 m, 1 ppm plume => 10-2 absorption fraction, with 10 GHz linewidth sharp lines: 10-7 detectable (noise limits), 105 resolution elements broad lines: 10-1 detectable (clutter limits), <102 resolution elements Solids: What is the concentration and absorption fraction (in reflection)? What is the signature, the linewidths, the clutter? Are their equivalent double resonance schemes for solids? 3-D Specificity Matrix

24. What are the Characteristics of Compact THz Technologies? 1. CW multiplied or fundamental oscillators 2. THz-TDS 3. FTFIR How do these Relate to Signatures? Quantifiable Figures of Merit

26. Spectroscopic Sensor Figures of Merit - I Sensitivity - ‘Dynamic Range’ is widely abused 1. Only source power in the signature bandwidth (Brightness - W/Hz) is useful - the rest often causes additional noise (a fundamental limit for FTFIR) 2. Detectors -NEP (W/Hz1/2) vs NEP’(W/Hz) 3. Noise and Dynamic Range Example: - 1 mW in a 100 Hz bandwidth, 3000K noise temperature =>dynamic range of >140 db This is good for the imager because the bandwidth of the reciever can be matched to the source and frame rate of the imager But people who build spectrometers never discuss dynamic range because the detection of a small amount of power in a narrow bandwidth is fundamentally different than the detection of a small change in a large amount of power. - in ideal noise limited spectrometer, the minimum detectable absorption is only - 90 db A 50 db Difference

27. Spectroscopic Sensor Figures of Merit - II Specificity 1. Scenario Clutter must be understood - spectroscopic clutter is much more complex than radar clutter. 2. ‘A’ vs ‘B’ demonstrations relate to a relatively small fraction of the scenarios of interest 3. Calculation of scenario dependant PFA or ROC is useful

28. 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?

29. What Needs to be Done to Enable the SMM/THz Spectral Region? 1. Classical penetrability, scatter, and specular reflection as a function of frequency and material. 2. What is the origin of linewidths in solids? 3. What are the signatures of solids and large molecules in the gas phase? Distribution in frequency relative to penetration? 4. What are the signatures of clutter for scenarios of interest? 5. Develop schemes for using time domain or other ‘X’ factors? 6. A closer connection between the technology community and the applications and science community. A litmus test: A reproducible, well founded signature science catalogue