19 May 1998 Nonlinear optical technique for advanced tunable IR lidar
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Abstract
A review of nonlinear optical techniques to be used in tunable far IR lidar, radar and spectrometer system is presented. As an example, a tunable IR remote sensing technology demonstrator system operating at 8-12 μm is described. It includes an OPO and OPA pumped by Nd:YAG laser as well as Raman emitter and receiver pumped by the OPA output. Relatively small variations of an OPA wavelength (1.85-2 μm)provide a broad operative range at far IR (8-12 μm). The unique feature of OPO is pumping by two phase conjugated beams. A pulse from the pump laser is transmitted through the OPO. A portion of the transmitted pulse is reflected in a phase conjugate cell, and the remaining pulse energy is semi- compressed in stimulated Brillouin scattering (SBS) cells. These phase conjugate (PC) cells are filled with highly purified and stable SiCl4 and GeCl4 (R=80%). This process reduces the OPO threshold as well as forms short and narrow linewidth pulses. Being amplified up to 140 mJ in a 2 ns pulse in the OPA, these pulses are directed to a hydrogen Raman emitter. Due to auxiliary pumps at 1064 nm and 1907 nm with total energy approximately 30 mJ providing phonon excitation, the SRS conversion of an OPA output in the Stokes wave starts from a relatively high phonon seed so a quantum efficiency of more than 50 percent at far IR is achieved. The high sensitive detector of far IR weak signals (~1000 photons)is based on a Raman-induced four wave mixing of these signals with a delayed OPA output. A subsequent readout of the Raman grating is performed using a 532 nm pulse. The Raman-shifted 683 nm pulse is proportional to that of a weak IR signal.
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Guerman A. Pasmanik, Alexander Z. Matveyev, Darrel G. Peterson, Alexander A. Shilov, Ivan V. Yakovlev, "Nonlinear optical technique for advanced tunable IR lidar", Proc. SPIE 3263, Nonlinear Optical Engineering, (19 May 1998); doi: 10.1117/12.308350; https://doi.org/10.1117/12.308350
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