25 October 1999 PPLN-OPO-based backscatter absorption gas imaging (BAGI) system and its application to the visualization of fugitive gas emissions
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Abstract
We report on a laser active imager suitable for the visualization of natural gas leaks and volatile organic compounds emitted by oil refineries. The described backscatter-absorption gas-imaging (BAGI) system employs a raster scanner in conjunction with a tunable continuous wave (cw) laser source. The imager creates real-time video imagery of a scene, while illuminating it with infrared laser light at a wavelength that is absorbed by the gas to be detected. Thus, gas plumes that otherwise cannot be seen by the human eye appear in BAGI images as dark clouds. In order to produce the high intensity infrared light that is needed to image natural gas and refinery by-products, we used a nonlinear frequency-conversion technique that employs the quasi-phase-matched crystal periodically poled LiNbO3. The crystal serves as the active medium in a cw optical parametric oscillator (OPO) that is pumped by a diode-pumped Nd:YAG laser. The output frequencies were selected to coincide with absorption features of general aliphatic species (2935 and 2968 cm-1), aromatics, such as benzene and toluene (3033 cm-1), and methane (3018 cm-1). The crystal was engineered to cover the desired spectral range using a fan-out design. This allows tuning of the OPO between 2832 and 3145 cm-1 in idler wavelength by simply translating the crystal at a fixed temperature. Presented data demonstrate the performance of this system for imaging species of interest at relevant concentrations and ranges up to about 30 m.
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Uta-Barbara Goers, Uta-Barbara Goers, Thomas J. Kulp, Thomas J. Kulp, Peter E. Powers, Peter E. Powers, Thomas G. McRae, Thomas G. McRae, } "PPLN-OPO-based backscatter absorption gas imaging (BAGI) system and its application to the visualization of fugitive gas emissions", Proc. SPIE 3758, Application of Tunable Diode and Other Infrared Sources for Atmospheric Studies and Industrial Processing Monitoring II, (25 October 1999); doi: 10.1117/12.366451; https://doi.org/10.1117/12.366451
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