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Proceedings Paper

Heterodyne lidar for chemical sensing
Author(s): Richard C. Oldenborg; Joe Tiee; Tom Shimada; Carl Wilson; Dennis Remelius; Jay Fox; Cynthia R. Swim
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Paper Abstract

The overall objective is to assess the detection performance of LWIR (long wavelength infrared) coherent Lidar systems that potentially possess enhanced effluent detection capabilities. Previous work conducted by Los Alamos has demonstrated that infrared DIfferential Absorption Lidar (DIAL) is capable of detecting chemicals in plumes from long standoff ranges. Our DIAL approach relied on the reflectivity of topographical targets to provide a strong return signal. With the inherent advantage of applying heterodyne transceivers to approach single-photon detection in LWIR, it is projected that marked improvements in detection range or in spatial coverage can be attained. In some cases, the added photon detection sensitivity could be utilized for sensing “soft targets”, such as atmospheric and threat aerosols where return signal strength is drastically reduced, as opposed to topographical targets. This would allow range resolved measurements and could lead to the mitigation of the limiting source of noise due to spectral/spatial/temporal variability of the ground scene. The ability to distinguish normal variations in the background from true chemical signatures is crucial to the further development of sensitive remote chemical sensing technologies. One main difficulty in demonstrating coherent DIAL detection is the development of suitable heterodyne transceivers that can achieve rapid multi-wavelength tuning required for obtaining spectral signature information. LANL has recently devised a novel multi-wavelength heterodyne transceiver concept that addresses this issue. A 5-KHz prototype coherent CO2 transceiver has been constructed and is being now used to help address important issues in remote CBW agent standoff detection. Laboratory measurements of signal-to-noise ratio (SNR) will be reported. Since the heterodyne detection scheme fundamentally has poor shot-to-shot signal statistics, in order to achieve sensitive detection limits, favorable averaging statistics have to be validated. The baseline coherent DIAL detection sensitivity that can be achieved averaging multiple laser pulses and by comparisons of different wavelengths will be demonstrated. Factors that are presently limiting performance and attempts to circumvent these issues will be discussed.

Paper Details

Date Published: 13 August 2004
PDF: 8 pages
Proc. SPIE 5416, Chemical and Biological Sensing V, (13 August 2004); doi: 10.1117/12.541425
Show Author Affiliations
Richard C. Oldenborg, Los Alamos National Lab. (United States)
Joe Tiee, Los Alamos National Lab. (United States)
Tom Shimada, Los Alamos National Lab. (United States)
Carl Wilson, Los Alamos National Lab. (United States)
Dennis Remelius, Los Alamos National Lab. (United States)
Jay Fox, Fox Physics Consulting (United States)
Cynthia R. Swim, U.S. Army Edgewood Chemical Biological Ctr. (United States)

Published in SPIE Proceedings Vol. 5416:
Chemical and Biological Sensing V
Patrick J. Gardner, Editor(s)

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