12 May 2016 Characterization and control of tunable quantum cascade laser beam parameters for stand-off spectroscopy
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Abstract
Infrared active stand-off detection techniques often employ high power tunable quantum cascade lasers (QCLs) for target illumination. Due to the distances involved, any fluctuation of the laser beam direction and/or beam profile is amplified at the sample position. If not accounted for, this leads to diminished performance (both sensitivity and selectivity) of the detection technique as a direct result of uncertainties in laser irradiance at each imaged pixel of the sample. This is especially true for detection approaches which illuminate a relatively small footprint at the target since the laser beam profile spatial fluctuations are often comparable to the (focused) laser spot size. Also, there is often a necessary trade-off between high output QCL power and beam quality. Therefore, precise characterization of the laser beam profile and direction as a function of laser properties (tuning wavelength, current and operating mode: pulsed or CW) is imperative. We present detailed measurements of beam profiles, beam wander and power fluctuations and their reproducibility as function of laser wavelength and stand-off distance for a commercially available tunable quantum cascade laser. We present strategies for improving beam quality by compensating for fluctuations using a motorized mirror and a pair of motorized lenses. We also investigate QCL mode hops and how they affect laser beam properties at the sample. Detailed mode-hop stability maps were measured.
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Robert Furstenberg, Robert Furstenberg, Christopher A. Kendziora, Christopher A. Kendziora, Michael R. Papantonakis, Michael R. Papantonakis, Viet Nguyen, Viet Nguyen, R. Andrew McGill, R. Andrew McGill, "Characterization and control of tunable quantum cascade laser beam parameters for stand-off spectroscopy", Proc. SPIE 9824, Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XVII, 98240L (12 May 2016); doi: 10.1117/12.2224003; https://doi.org/10.1117/12.2224003
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