22 May 2015 Detection of chemical clouds using widely tunable quantum cascade lasers
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Widely tunable quantum cascade lasers (QCLs) spanning the long-wave infrared (LWIR) atmospheric transmission window and an HgCdTe detector were incorporated into a transceiver having a 50-mm-diameter transmit/receive aperture. The transceiver was used in combination with a 50-mm-diameter hollow retro-reflector for the open-path detection of chemical clouds. Two rapidly tunable external-cavity QCLs spanned the wavelength range of 7.5 to 12.8 m. Open-path transmission measurements were made over round-trip path-lengths of up to 562 meters. Freon-132a and other gases were sprayed into the beam path and the concentration-length (CL) product was measured as a function of time. The system exhibited a noise-equivalent concentration (NEC) of 3 ppb for Freon-132a given a round-trip path of 310 meters. Algorithms based on correlation methods were used to both identify the gases and determine their CLproducts as a function of time.
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Anish K. Goyal, Anish K. Goyal, Petros Kotidis, Petros Kotidis, Erik R. Deutsch, Erik R. Deutsch, Ninghui Zhu, Ninghui Zhu, Mark Norman, Mark Norman, Jim Ye, Jim Ye, Kostas Zafiriou, Kostas Zafiriou, Alexander Mazurenko, Alexander Mazurenko, "Detection of chemical clouds using widely tunable quantum cascade lasers", Proc. SPIE 9455, Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XVI, 94550L (22 May 2015); doi: 10.1117/12.2177527; https://doi.org/10.1117/12.2177527

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