Vibrational spectroscopy standoff detection of explosives

Abstract

Standoff infrared and Raman spectroscopy (SIRS and SRS) detection systems were designed from commercial instrumentation and successfully tested in remote detection of high explosives (HE). The SIRS system was configured by coupling a Fourier-transform infrared interferometer to a gold mirror and detector. The SRS instrument was built by fiber coupling a spectrograph to a reflective telescope. HE samples were detected on stainless steel surfaces as thin films (2-30 microg/cm(2)) for SIRS experiments and as particles (3-85 mg) for SRS measurements. Nitroaromatic HEs: TNT, DNT, RDX, C4, and Semtex-H and TATP cyclic peroxide homemade explosive were used as targets. For the SIRS experiments, samples were placed at increasing distances and an infrared beam was reflected from the stainless steel surfaces coated with the target chemicals at an angle of approximately 180 degrees from surface normal. Stainless steel plates containing TNT and RDX were first characterized for coverage distribution and surface concentration by reflection-absorption infrared spectroscopy. Targets were then placed at the standoff distance and SIRS spectra were collected in active reflectance mode. Limits of detection (LOD) were determined for all distances measured for the target HE. LOD values of 18 and 20 microg/cm(2) were obtained for TNT and RDX, respectively, for the SIR longest standoff distance measured. For SRS experiments, as low as 3 mg of TNT and RDX were detected at 7 m source-target distance employing 488 and 514.5 nm excitation wavelengths. The first detection and quantification study of the important formulation C4 is reported. Detection limits as function of laser powers and acquisition times and at a standoff distance of 7 m were obtained.

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“…(3) and the average difference in assigned peaks in spectral range 0-4270 cm -1 is about 2 cm -1 . Standoff spectrum of C4 is in a good agreement with the spectrum obtained by other authors [5][6][7][8][9] and the average difference in assigned peaks in spectral range 0 -4270 cm -1 is about 2 cm -1 . One of the aims of the study is to study the influence of integration time and laser power on Raman cross section and to determine the integration time and laser power at which the optimal signal to noise (S/N) ratio is achieved for standoff Raman spectra.…”

Standoff Raman Detection of Explosive Materials Using a Small Raman Spectroscopy System

“…The positions of major bands in TNT spectrum detected via standoff Raman spectroscopy consistent with reference micro Raman spectrum as clearly shown in Fig. (8) as well as consistent with previously published experimental data [6,7]. The average difference of peak shift is about 1 cm -1 from that of micro Raman spectroscopy and the average difference of peak shift was 2 cm -1 from that of Samuel et al [6].…”

Detection of Trace Explosive Materials by Standoff Raman Spectroscopy System

“…The LOD obtained in this study is compared to the other author PachecoLondono et al [13]. Their LOD calculated for C4 was 3 mg at standoff distance of 7 meters, using continuous wave SRS system operating at wavelength of 488 nm, integration time of 50 s, laser power of 500 mW and laser spot size is 3.5 mm.…”