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The Physics and Chemistry of Analysis in the Submillimeter/Terahertz Spectral Region

The Physics and Chemistry of Analysis in the Submillimeter/Terahertz Spectral Region Frank C. De Lucia The Microwave Laboratory Ohio State University Columbus, OH 43210 August 30, 2005 American Chemical Society Washington, DC. PEOPLE Frank C. De Lucia - Professor OSU

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The Physics and Chemistry of Analysis in the Submillimeter/Terahertz Spectral Region

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  1. The Physics and Chemistry of Analysis in the Submillimeter/Terahertz Spectral Region Frank C. De Lucia The Microwave Laboratory Ohio State University Columbus, OH 43210 August 30, 2005 American Chemical Society Washington, DC

  2. PEOPLE Frank C. De Lucia - Professor OSU Eric Herbst - Professor OSU Brenda Winnewisser - Adj. Professor OSU Manfred Winnewisser - Adj. Professor OSU Paul Helminger - Professor USA Doug Petkie - Professor WSU Markus Behnke - Research Associate Atsuko Maeda - Research Associate Ivan Medvedev - Research Associate Andrey Meshkov - Graduate Student TJ Ronningen - Graduate Student Laszlo Sarkozy - Graduate Student David Graff - Graduate Student Bryan Hern - Undergraduate Student Drew Steigerwald - Undergraduate Student John Hoftiezer - Electrical Engineer

  3. Bo e- SMM Analytical Gap H2O CO2 100 H2O O2 Attenuation (dB/km) 10 H2O H2O CO2 CO2 1 H2O H2O O3 0.1 RF Microwave Visible Millimeter/Submillimeter Infrared 0.01 10 GHz 0.1 THz 1 THz 10 THz 100 THz 1000 THz Frequency 3 cm 3 mm 0.3 mm 30 mm 3 mm 300 nm Wavelength Bruker BioSpin MRI International Light THERE ARE NO ‘PUBLIC’ APPLICATIONS OF THE THz Bruker FTIR’s

  4. Overview What do Analytical Chemists Care About? SMM/THz Technology - pulsed and cw Noise Brightness SMM/THz Systems in ‘Scientific’ Applications A Clear Path to a ‘Public’ Application Fast Scan Submillimeter Spectroscopy Technique (FASSST) Gas Analysis

  5. What do Analytical Chemists Care About? Specificity Sensitivity Generality Size Cost Speed Ease of Use Comparison with Alternatives

  6. There are Established SMM Applications Technologies which approach fundamental limits Fundamental Molecular Studies - Spectroscopy, Dynamics Laboratory Astrophysics Science in the Field/Remote sensing Interstellar medium, stellar formation Upper atmospheric chemistry

  7. A CLEAR PATH TO GAS ANALYSIS Opt. Lett. 14, 1128-1130(1989) HP ~1975

  8. TRANSMIT POWER Fundamental IMPATTs Varactor Multipliers CW Power (mW) Semiconductor Lasers Fundamental RTDs GaAs Photomixers Kindly provided by E. Brown

  9. 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

  10. ‘Absolute’ Specificity in a Mixture of 20 Gases

  11. #09 Acrylonitrile Library Combined Spectrum Gas Identification in Mixture of 20 Gases Blow-ups of Combined Spectrum Library Identification of Acrylonitrile

  12. 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 1 10 100 1000 Number of Lines(Fingerprint Elements)

  13. FASSST Spectrometer Diagram VCO 10.3 – 10.8 GHz Frequency Reference 10.5 GHz Frequency Standard Mixer X8 Multiplier W-band Harmonic 10 MHz Comb Generator Amplifier Mixer W-band Amplifier 75-110 GHz Amplifier Low Pass Filter 10kHz – 1MHz x24 X3 Multiplier W-band Computer DAQ Gas Cell Detector

  14. COMMUNICATIONS WIRELESS TECHNOLOGY*[can make, very small, low power, and very cheap] + commodity microwave chips + 3 (very special) diodes = cw THz module *The government alone can’t afford to develop the THz, only the market can make us mature

  15. 1 second sweep time over whole spectrum 300 seconds integration on resonance X 107 sensitivity plus ‘absolute’ specificity

  16. This is Great, But What About Real Problems in the Real World? To this end we’ve: Built the compact solid state system (but not cheaply yet!). Developed appropriate control and calibration software. Built the automated identification and quantification software and used it successfully on challenging complex mixtures. Considered sensitivity, sampling, and preconcentration strategies. Considered in detail issues of background and clutter, especially that expected from the atmosphere.

  17. USACHPPM Toxic Industrial Chemical List* in Atmospheric Clutter Background *Excludes gases without dipole or vapor pressure: Chlorine, diborane, hydrazine, parathion, sulfuric acid

  18. x3 multiplier W-band amplifier x8 multiplier HRL Chip Set 0.5 cm AT THIS POINT IN TIME -- GAS ANALYSIS EMERGES FROM A CONFLUENCE OF SCIENCE AND TECHNOLOGY Physics Always Favorable (1955) HP 40 GHz MW Spectrometer(1974) OSU BWO Based 300 GHz FASSST (1998) Microfabrication => small, inexpensive in quantity (2004) Solid StateWaveguide Block Components (2001) Growth in computing power to handle information Broadband wireless market

  19. What do Analytical Chemists Care About? Specificity ‘Absolute’, Even in Complex Mixtures Atmospheric/Background Clutter Minimal Sensitivity 10-15 - 10-18 Moles Generality Requires Dipole Moment, Vapor Pressure Size Now: <<1 ft3; potential for a few in3 Cost (in quantity): ‘Wireless’ Chips, 3 Diodes, Small Vacuum System, Data Analysis Speed 10-6 s to 3+ s Ease of Use Automated Quantification in Complex Mixtures Comparison with Alternatives ???

  20. Research and Development Issues 1. Gas/Particle Capture and Concentration 2. System Strategy Frequency control and measurement Signal recovery/dynamic range/noise spectra 3. Spectroscopic Theory/Libraries 4. Clutter analysis 5. Information theory 6. Extreme miniaturization 7. Large molecule limit 8. Specialized monitors

  21. Source Brightness! 10-2 photons/pulse/MHz

  22. THz Spectroscopy SMM/FIR Spectroscopy (0.02223482) (0.18331000) (0.38019757) (0.44800137) 0.55693607 (0.62070183) 0.75203305 (0.91617141) (0.97031518) 0.98792686 1.09736463 1.11334350 1.15312557 1.16291446 1.20764261 1.22879089 1.41062289 Phys. Rev. A5, 487 (1972). Int. J. Infrared and Millimeter Waves 4, 505 (1983). Appl. Phys. Lett. 42, 309 (1983). Opt. Lett. 14, 1128-1130 (1989).

  23. Spectra as a Function of Molecular Size Population of levels Jmax 18 Jmax 30 Jmax 55 Jmax 96 Jmax 305

  24. REFERENCES Optics and Photonics News (August 2003) and “Spectroscopy in the Terahertz Region,” in Sensing with Terahertz Radiation, D. Mittleman, ed. Springer, Berlin (2003).

  25. THE ENERGETICS 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 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 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

  26. PHYSICS AND THz SOURCE REQUIREMENTS Source Brightness Doppler Width ~ 1 MHz 1 mW in 1 MHz has same brightness as 1 kW in 1 THz 10-10 W in 1 MHz has same brightness as 10-4 W in 1 THz

  27. THE ‘NATIVE’ THz APPLICATION: GAS SENSING WITH ‘ABSOLUTE’ SPECIFICITY In the context of DARPATECH 2004, our laboratory’s work in this area was highlighted as a part of their presentation as: “One such opportunity is the identification of chemical threats. Low-pressure gases have astonishingly selective signatures in this region. In MTO’s recently completed Terahertz Technology for Sensing and Satellite Communications program, a relatively compact chemical sensor was developed and shown to have incredible absolute specificity even when dealing with very complicated mixtures. Further advances could lead to very inexpensive and portable systems.” A PROBLEM:This is such a natural application that many really bad systems have been proposed/sold that are completely incapable of living up to their claims. EVEN WORSE: It is widely claimed that systems like our cw submillimeter system are ‘plagued by noise’ and that only THz-TDS systems are viable.

  28. VERY REMOTE SUBMILLIMETER SENSING Spectrum of the 325 - 360 GHz survey of the Orion molecular cloud taken by the CSO instrument on Mauna Kea. Details of the 338 - 339 GHz portion of the 325 - 360 GHz survey of the Orion molecular cloud taken by the CSO instrument on Mauna Kea.

  29. Phenomenology and SMM/THz Technology What is the Physics of 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?) How does the Physics interact with the Technology Where are the interactions? What is a THz? Source brightness, time dependence Detector sensitivity, background noise

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