Mobile system for open-path trace gas detection in the mid-infrared using a Raman-shifted Cr:LiSAF source

Paula R. Wamsley; Carl S. Weimer; Jeffrey T. Applegate; Stuart P. Beaton; Brian S. Beyer

doi:10.1117/12.366427

22 October 1999 Mobile system for open-path trace gas detection in the mid-infrared using a Raman-shifted Cr:LiSAF source

Paula R. Wamsley, Carl S. Weimer, Jeffrey T. Applegate, Stuart P. Beaton, Brian S. Beyer

Author Affiliations +

Proceedings Volume 3757, Application of Lidar to Current Atmospheric Topics III; (1999) https://doi.org/10.1117/12.366427
Event: SPIE's International Symposium on Optical Science, Engineering, and Instrumentation, 1999, Denver, CO, United States

Abstract

Many trace atmospheric gas constituents have optical absorption bands in the 2 - 5 micrometers atmospheric transmission window. Remote sensing of these compounds is possible with an appropriate laser source. We use stimulated Raman scattering in hydrogen to shift pulsed, Cr:LiSAF laser emission from the near infrared to this mid-infrared band. Injection seeding the oscillator with a spectrally narrow, low-power diode laser produces a tunable, spectroscopic grade source. We have combined this laser source with transmitting and receiving optics in order to make double- ended, long-path DIAL measurements. For example, we are able to detect ambient levels of water and methane and trace levels of ethane over a two mile, round-trip path. Spectral control is critical for making these measurements for several reasons. First, the DIAL technique requires a spectrally narrow source to tune across the narrow absorption bands of molecules with absorption features in the 2 - 5 micrometers band. Second, good spectral control allows species-specific detection when there are target species with closely spaced absorption features. Third, strong water vapor and CO₂ absorption bands are common throughout the 2 - 5 micrometers band causing large fluctuations in the background transmission. Good spectral control enables species specific detection within this highly variable transmission background.

Citation Download Citation

Paula R. Wamsley, Carl S. Weimer, Jeffrey T. Applegate, Stuart P. Beaton, and Brian S. Beyer "Mobile system for open-path trace gas detection in the mid-infrared using a Raman-shifted Cr:LiSAF source", Proc. SPIE 3757, Application of Lidar to Current Atmospheric Topics III, (22 October 1999); https://doi.org/10.1117/12.366427

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