THz Wave Photonics

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THz Wave Photonics0621522Xi-Cheng Zhang,Rensselaer Polytechnic InstituteIntellectual merit: After the first demonstration of terahertz (THz) wave time-domain spectroscopy in the late 80's, the time-domain THz community commonly uses coherent emitters and detectors for pulsed THz waves, which are mainly limited to the photoconductive dipole antennas and electro-optic crystals. Ambient air, a third-order nonlinear material, should exhibit a remarkable performance for the generation and detection of pulsed THz waves with an intense femtosecond laser beam. The proposed project is significant, since visible light dispersion in air is extremely low, a THz system with an all-air based emitter and sensor could offer a bandwidth unprecedented by any other pulsed THz wave sensor, which is limited only by the optical pulse bandwidth. In the air, the attenuation for THz waves and visible beams are on the order of 100 dB/km and 0.01 dB/km, respectively. It was previously considered impossible to perform long distance THz wave sensing and spectroscopy, due to severe water vapor attenuation (100 dB/km). Long distance THz sensing is now feasible since achieving low attenuation at the visible range (0.01 dB/km) by sending an optical beam to locally generate and detect THz waves near the target. Thus proving that using air as THz wave emitters and sensors would provide us the greatest flexibility in remote sensing and spectroscopy. Broader impact: Recent years have seen a plethora of significant advances as THz sources and more sensitive detectors open up a range of potential applications. Applications including semiconductor characterization, non-destructive testing, tomographic imaging, label-free genetic analysis, cellular level imaging, and chemical/ biological sensing have thrust THz research, from relative obscurity, into new heights. The proposed research on the air sensor will provide a key enabling technology for interdisciplinary research, as well as advance numerous sensing and imaging concepts in the THz frequency range, with an immediate impact on non-destructive analysis, a short-term application for homeland security and a longer-term interest in biomedicine. Moreover, this research will make significant contributions to student education, academic research, outreach activities, and instrumentation development.