29 May 2014 Spatially offset hyperspectral stand-off Raman imaging for explosive detection inside containers
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Abstract
A stand-off Raman imaging system for the identification of explosive traces was modified for the analysis of substances in containers which are non-transparent to the human eye. This extends its application from trace detection of threat materials to the investigation of suspicious container content. Despite its limitation to containers that are opaque to the facilitated laser, the combination of Spatial Offset Raman Spectroscopy (SORS) with stand-off Raman imaging allows to collect spectral data from a broad range of different spatial offsets simultaneously. This is a significant advantage over SORS with predefined offset, since the ideal offset is unknown prior to the measurement and depends on the container material as well as the sample content. Here the detection of sodium chlorate in a white plastic bottle is shown. A 532nm-laser (pulse length 5ns, repetition 50kHz) was focused to a diameter of 10mm at 10m. A 1500mm Schmidt-Cassegrain telescope with a 152.4mm diameter collected the scattered light. An edge filter removed inelastically scattered laser light and a liquid crystal tunable filter was used to select 0.25nm broad wavelength ranges between 480 and 720nm. The sample area of 50×50mm was imaged on 1024×1024 pixels of an ICCD camera. For the conducted experiments an ICCD gate time of 5ns was selected and 70μJ-laser pulses were accumulated during 1s for each wavelength.
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Bernhard Zachhuber, Henric Östmark, Torgny Carlsson, "Spatially offset hyperspectral stand-off Raman imaging for explosive detection inside containers", Proc. SPIE 9073, Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XV, 90730J (29 May 2014); doi: 10.1117/12.2053251; https://doi.org/10.1117/12.2053251
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