6 October 2007 Mid-infrared, broadly tunable, active hyperspectral imaging system for the detection of gaseous hydrocarbon species
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We describe a compact mid-infrared active spectroscopic imaging system for the rapid, stand-off detection of gas / chemical agents. Based upon the back-scatter absorption gas imaging (BAGI) technique, the system utilises a miniaturised, extremely efficient all solid state intracavity optical parametric oscillator (OPO) as the imaging illumination source. The OPO produces up to 250mW of tunable radiation in the signal and idler fields over the range 1.3-4.5μm, for a diode pump power of only 3W. Due to the nature of the nonlinear crystal employed within the OPO, the system can be tuned across its spectral range in ~1 second. We obviate the very high cost and complexity of a cooled MCT or InSb video array by raster-scanning the collimated illumination beam over the area of interest and reconstructing the image by sampling the back-scattered radiation with a single element MCT photo-detector at each pixel point. This approach also improves the ultimate signal to noise ratio. Video-like frame rates of 10 f.p.s. have been demonstrated via this technique. The range limit of the instrument is currently <10 meters which is limited by the detector we currently employ. We demonstrate how the system has been used to detect, in real time, leaks of multi-species hydrocarbon gases.
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David J. M. Stothard, Cameron F. Rae, Mark Ross, and Malcolm H. Dunn "Mid-infrared, broadly tunable, active hyperspectral imaging system for the detection of gaseous hydrocarbon species", Proc. SPIE 6737, Electro-Optical and Infrared Systems: Technology and Applications IV, 673705 (6 October 2007); doi: 10.1117/12.738010; https://doi.org/10.1117/12.738010

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