Physics Driven Challenges and Opportunities in the Submillimeter/Terahertz Spectral Region

1. Penetration Resolution Spectroscopic Identification Physics Driven Challenges and Opportunities in the Submillimeter/Terahertz Spectral Region Frank C. De Lucia Department of Physics Ohio State University GOMACHTech, March 20, 2006 San Diego, CA 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.

2. Preview of Take Home Messages: To Realize the Potential of the SMM/THz 1. Many potential applications have been identified, but no ‘public’ applications have resulted. 2. Clear paths exist to legacy ‘public’ applications: Imaging and point gas detection. 3. Often it is not possible to evaluate the potential of proposed applications because we do not know (or do not consider) the phenomenology and/or the signature science. 4. An unusually broad range of SMM/THz technical approaches exist - very different capabilities - first we need to better understand figures of merit - then the relation between capabilities and proposed applications 5. Concepts are often far ahead of analysis. 6. We need to bring together ‘concept development’ (e. g. NYT article) with knowledge of phenomenology and signature science. 7. As we get closer to applications and deal with user communities, questions become harder - gas phase sensing as an example. 8. In addition to the well known technical ‘gap in the electromagnetic spectrum’ there is also a scientific and phenomenological one.

3. What’s a THz? 0.1 THz ~1/60 kT - clearly classical l = 3 mm 10 THz > kT - quantum regime l = 0.03 mm 30 THz ~ frequency of CO2 laser l = 0.01 mm What’s a Name Mean? Millimeter, NearMillimeter, Submillimeter, Terahertz, Far Infrared With a broad definition, what properties are available at a particular choice of frequency? Jumping the ‘gap in the electromagnetic spectrum’ is not the same as closing it

4. The government alone can’t afford to develop the THz, only the market can make us a mature, ‘public’ tool Electromagnetic Phenomenology What is so favorable about the SMM/THz? The SMM/THz is very quiet: 1 mW/MHz => 1014 K 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 In comparison to the MW, the SMM/THz has a lot of bandwidth The commercial wireless market will provide us with a cheap technology It should be possible to engineer small (because of the short wavelength) and low power (because the background is quiet/the quanta is small) devices and systems

5. 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?

6. Two MW/SMM Legacy ‘Public’ Applications -- Clear, but Challenging Paths to Success -- IMAGING ANALYTICAL CHEMISTRY

7. I. Applications Matrix as introduction to Signature Science

8. 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

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 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?

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) 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

11. “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

12. “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

13. “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. Parallel and On Going MM/SMM Science [Field Technology and Systems Grew out of Lab Science] NASA JPL catalog HITRAN, KOLN, GEISA data bases Data Base Meetings HITRAN NASA The GEISA/IASI spectroscopic database

16. Image Comparisons: Angular Diversity Cold Sky Illumination at 94 GHz ‘Uniform’ Passive Illumination at 94 GHz MODES Co-propagated coherent illumination (Active) Diffuse thermal illumination (‘Passive’ ?) Diffuse coherent illumination (‘Active’ ?) Thermal emission (Passive) THz Passive Thermal Emission Thermal Emission on Warm at 650 GHz Background ~15 Degree Thermal Illumination at 650 GHz Shadow gram of metallic object reflecting diffuse colder room Contrast of metal within angular diversity of illuminator Thermal Radiation from Object

17. Signatures Classical Electricity and Magnetism MW, MMW,SubMMW, THz, FIR, IR Quantum Mechanical Spectroscopy Gases (MW, MMW,SubMMW, THz, FIR, IR) Solids (Which regions?) Combination Resonances Molecule in a cavity Naturally occurring equivalent?

18. From Concepts to Real Systems User to developer: Questions become harder What are the details of the signature that we propose to sense? -image, spectra, texture, combination? How do we separate signatures from natural background and confusers? How will the technique work in scenarios of interest? What are current and medium term technical limits? What are near term and ultimate size, cost, power? What are the ultimate scientific limits? How does this compare to alternatives?

19. Phenomenology: What is the Physics of the Interactions? Separate into Three Classes According to 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?)

20. An Example: High Resolution Gas Phase Spectra

21. Clutter Spectrum of a Polluted Urban Atmosphere

22. Signatures: Explosives Spectra

23. MORE INTERCOMPARISIONS This problem of repeated presentation of clearly spurious results is not restricted to THz solid state spectra - It exists in the gas phase as well.

24. 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.

25. Black Forest Ham THz Solids FAMILIES OF FALSE ALARM RATES THz Rotational Spectroscopy 500 Molecules PFA=10-12 PFA=10-9 PFA=10-6 PFA=10-3 Log of Number of Resolution Elements 50 Molecules PFA=10-12 PFA=10-9 PFA=10-6 PFA=10-3 GC/MS/IMS 2 Molecules PFA=10-12 PFA=10-9 PFA=10-6 PFA=10-3 IR-Vibration Figure 2. False alarm rate as a function of the number of fingerprint elements (resolution lines) of a particular species and the number of resolution elements of the sensor’s operational swept frequency band. 1 10 100 1000 Number of Lines(Fingerprint Elements)

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

28. 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

29. IV. 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

32. Spectroscopic Sensor Figures of Merit Sensitivity - ‘Dynamic Range’ is widely abused 1. Only source power within the signature bandwidth(Brightness) 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 but people who build spectrometers never discuss dynamic range because the detection of a small amount of power is fundamentally different than the detection of a small change in a large amount of power. - in ideal noise limited system, the minimum absorption for this system is only - 90 db 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

33. V. Applications Matrix as summary of Signature Science

34. + ‘X’? 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/other solids close, sort, sm obstruct some materials Pharmaceuticals, bio close, sort, sm obstruct some materials Penetration Solid state spectra

35. What Needs to be Done to Enable the SMM/THz Spectral Region? 1. 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? Strategies for minimizing the impact of the atmosphere on these signatures 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

36. PEOPLE Frank C. De Lucia - Professor OSU 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

37. That’s Hot - A THz Application KILLER APs FOR THE THz? Legacy applications Classical Imaging Chemical Sensing The Hot New Applications on the Web Detect cancer via spectral signatures See through walls People under rubble Remotely detect buried objects, underground toxins, concealed nuclear materials, biological aerosols, objects’ chemical composition