Image analysis of explosives fingerprint contamination using a Raman imaging spectrometer

The characterization of the type and quanity of explosives residue left behind as fingerprints is critical for the problem of trace explosives detection as well as forensic investigation. A nondestructive analytical technique has to be used to identify the energetic component of the explosive from the plasticizers, dyes, and fingerprint oils that make up the background. Raman microspectroscopy has been demonstrated in the past to separate explosive particulate from other residue in a microscopic image by filtering out other spectra except the region of the strong bands displayed by PETN and RDX using He-Ne excitation. In addition, gray level/measurements have been done on features of the sample, captured under white light onto a CCD, to obtain quantitative data about size and volume distribution. The objective of this paper will be to show how integrated line images of the sample, captured with high spectral resolution using a scanning Raman spectrometer, can be used to separate out components in the image scene captured by the CCD. This paper will also show how confocal scanning through the depth of the sample, while taking an image, can be used to come up with a quantitative measure of the concentration of chosen components in the entire image. The special instrumentation used for the work will be shown as well as any modifications done to it to obtain a protocol for analysis. The image analysis results will be presented of actual fingerprint samples containing plastic explosives. The variance between the Raman imaging method and other more traditional destructive methods for doing quantitative analysis will be presented. And the probability of doing direct Raman microspectroscopy in the UV region without any background subtraction will be determined for its potential for doing in-situ analysis for explosives detection.