We present our work on stand-off Raman detection of explosives and related compounds. Our system employs 532 or 355 nm laser excitation wavelengths, operating at 10 Hz with a 4.4 ns pulse length and variable pulse energy (maximum 180 mJ/pulse at 532 nm and 120 mJ/pulse at 355 nm). The Raman scattered light is collected by a co-axially aligned 6" telescope and then transferred via a fiber optic cable and spectrograph to a fast gating iCCD camera capable of gating at 500 ps. We present results including the effect of different excitation wavelengths, showing that 355 nm excitation gives rise to significantly stronger stand-off Raman signals compared to that of 532 nm. We also show the effect of appropriate detector gating widths for discrimination of ambient light and the reduction of high background signals in the obtained Raman spectra. Our system can be used to identify explosives and their precursors in both bulk and trace forms such as RDX and PETN in the low mg range and TNT in the 700 μg range at a distance of 20 m, as well as detection of a 1% or greater H₂O₂ solution at a distance of 6.3 m.

Date Published: 12 October 2010
PDF: 10 pages
Proc. SPIE 7838, Optics and Photonics for Counterterrorism and Crime Fighting VI and Optical Materials in Defence Systems Technology VII, 78380F (12 October 2010); doi: 10.1117/12.864564

Published in SPIE Proceedings Vol. 7838:
Optics and Photonics for Counterterrorism and Crime Fighting VI and Optical Materials in Defence Systems Technology VII
Colin Lewis; Roberto Zamboni; François Kajzar; Doug Burgess; Emily M. Heckman, Editor(s)