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EE243 Quantum Electronics Seminar

EE243 Quantum Electronics Seminar. Robb Walters Thomas J. Watson Laboratory of Applied Physics California Institute of Technology. Topics in Terahertz Optics . Terahertz. Frequencies from 0.3 to 30 THz (Semiconductor Max to CO 2 Lasers)

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EE243 Quantum Electronics Seminar

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  1. EE243 Quantum Electronics Seminar Robb Walters Thomas J. Watson Laboratory of Applied Physics California Institute of Technology Topics in Terahertz Optics

  2. Terahertz • Frequencies from 0.3 to 30 THz (Semiconductor Max to CO2 Lasers) • Wavelengths: 30um to 1mm (bigger than many bio systems) • Quanta from 1 - 100 meV (lots of absorbers/emitters) • Why all the interest? • TDS improvements • Bio Imaging (CT) • Homeland Defense • LO for Astronomy (98% of photons) Quantum Electonics Seminar

  3. THz Imaging Comparatively good penetration without damage to tissue as in xray tomography… Sensitivity to water content allows for discrimination of tissue types… Quantum Electonics Seminar

  4. Generation of THz GHz homodyne Heterodyne Ti:Sapphire+NIR Photo-conduction Requires 10kG Field Quantum Electonics Seminar

  5. Optically Pumped THz Lasers Manley-Rowe Efficiency Limit: half the ratio of frequencies (here, 4%) (Typically <0.1%; Record is 1%.) Quantum Electonics Seminar

  6. Currently deployed at the South Pole, airborne systems, included in a satellite scheduled for launch next year that will study the ozone layer (AURA) Optically Pumped THz Lasers Spatial Mode Profile at 2.5THz. Quantum Electonics Seminar

  7. Photoconductive Emitters Bandwidth is inversely proportional to pump pulse duration. (Laser pulse closes the circuit.) Dry N2 Quantum Electonics Seminar

  8. THz Quantum Cascade Laser 104 repetitions in active region Laser is 180um by 3.1mm Current Nature May 2002… Quantum Electonics Seminar

  9. THz Quantum Cascade Laser Problems with heat. Duty cycle is 0.003% on solid lines; 0.5% on dashed. Quantum Electonics Seminar

  10. Free Space Electro-optic Crystal Detector ZnTe …comparable electro-optic figure of merit to LiTaO3 without the limitations associated with intrinsic birefringence and a reduced sensitivity to thermal fluctuations. Quantum Electonics Seminar

  11. ZnTe sensitivity (blind spots) 5.2 = ZnTe TO phonon 8.0 = GaAs TO phonon (photoconduction source) Highest resolved absorption at 32.3 THz is a “symmetric stretching vibration of CF2” Transmission of PTFE shows useful bandwidth of ZnTe. Quantum Electonics Seminar

  12. Bolometers Fancy bolometers use superconducting elements at the edge of transistions and SQUIDs to measure current fluctuations… All require cryogenic cooling for acceptable performance. Quantum Electonics Seminar

  13. THz (Aperture-less) NSOM Recent work from RPI group. (APL 10/13/2003) Quantum Electonics Seminar

  14. THz NSOM Scan of a 1um W tip held 200nm over 10um wide lines of Au. THz modulation is 0.2 to 0.6% of the total received power. Resolution is about 3mm = l/50 After 10 minutes… Quantum Electonics Seminar

  15. With a smaller NSOM tip… 100nm tip radius gives 150nm resolution (l/1000) …but They still see about 0.4% modulation, while they had predicted 1000 times less signal for a smaller spherical tip (0.1 R) They suggest local field enhancement due to “antenna” geometry (of 1000) Quantum Electonics Seminar

  16. OP THz Lasers: A white paper by Eric R. Mueller of Coherent-DEOS Industrial Physicist (8/9 2003 Edition) Article by the same guy Photoconduction (Broadband) Emitters and TDS (APL10/13, 2003) Shen et al: Ultrabroadband terahertz radiation from low-temperature-grown GaAs photoconductive emitters THz Quantum Cascade Laser Nature May 9, 2002 - Terahertz Semiconductor Heterostructure Laser General discussion in Nature “News Feature” (August 14, 2003) ZnTe ElectroOptic Detectos APL paper from 1996: Wu et al: Broadband detection capability of ZnTe electro-optic field detectors THz NSOM: (APL10/13) Chen et al: Terahertz imaging with nanometer resolution Optics Letters 12/15/2001: Filin et al: Time Domain Differentiation of THz Pulses References Kersting and Zhang at RPI Beere at Cambridge These papers come from: Quantum Electonics Seminar

  17. Since we have time… Gratings: 200nm thick gold lines, periods from 10-40um (subwavelength) l=130um Zero Order Transmission Superluminal??? Quantum Electonics Seminar

  18. …the time derivative Quantum Electonics Seminar

  19. As Predicted from Diffraction Theory 0 1 For m=zero Quantum Electonics Seminar

  20. Special case of sub-wavelength grating Expand in (k*l) to 4th order… Quantum Electonics Seminar

  21. Accuracy of Approximation l=130mm As the grating gets smaller, the approximation is more accurate (but the transmitted signal decreases too…) Quantum Electonics Seminar

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