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Proceedings Paper

Investigation of standoff explosives detection via photothermal/photoacoustic interferometry
Author(s): Pak S. Cho; Robert M. Jones; Timothy Shuman; Daniel Scoglietti; Geof Harston
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Paper Abstract

Progress in standoff detection of surface-bound explosives residue using photothermal and photoacoustic (PT/PA) imaging and spectroscopy has been reported recently. Photothermal/photoacoustic interferometry (PTI), a variation of the aforementioned techniques, is a candidate for standoff detection as a result of its non-contact and non-destructive approach. In PTI, the transient PT/PA hydrodynamic response produced by impulsive infra-red laser excitation(s) are detected by an overlapping focused probe laser beam. The return back-scattered/reflected probe laser beam is collected and coupled into a single-mode optical fiber. The PT/PA-induced perturbation on the return probe laser, in the form of phase or amplitude modulation or both, is extracted interferometrically. The resulting quadrature signals are digitized and processed to recover the minute PT/PA dynamics above background noise. Characteristic spectra for materials can be obtained by quantifying the PT response as a function of excitation(s) wavelength. The CW probe laser, operating in the 1550 nm range, and the constituents of the coherent detection system are commercial off-the-shelf components. A commercially available and continuously tunable quantum cascade laser (QCL) with output pulse energies up to 50 nJ was employed to generate the PT/PA spectra in the 8.8-10.2 μm range. PTI detected absorption spectra were collected for HMX, RDX, and PETN, with the probe laser system positioned 5 meters away from the explosives targets. In addition, PTI measurements of the stimulated Raman (SR) spectra of ammonium nitrate and 2,4,6-trinitrotoluene obtained using a near-IR OPO laser are described. We believe this is the first-ever application of photothermal techniques to the measurement of the SR effect on solid explosive materials at meaningful standoff distances.

Paper Details

Date Published: 3 June 2011
PDF: 15 pages
Proc. SPIE 8018, Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XII, 80181T (3 June 2011); doi: 10.1117/12.883027
Show Author Affiliations
Pak S. Cho, Celight, Inc. (United States)
Robert M. Jones, ITT Corp. (United States)
Timothy Shuman, ITT Corp. (United States)
Daniel Scoglietti, ITT Corp. (United States)
Geof Harston, Celight, Inc. (United States)


Published in SPIE Proceedings Vol. 8018:
Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XII
Augustus W. Fountain; Patrick J. Gardner, Editor(s)

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