We have demonstrated that standoff Raman spectra of some nitrates could be obtained at distances ranging from 20 meters to 250 meters using an 11-inch reflecting telescope and a continuous wavelength 785 nm laser of 400 mW power coupled with a small portable spectrometer. The measurements were taken during both day and night, indoors and outdoors, for various integration times. Detection and identification of chemical and biological hazards within the forensic and homeland security contexts requires conducting the analysis in field while adapting a non-contact approach to the hazard. In this paper, we report the adequacy of a standoff Raman system with a 785nm laser for remote detection and identification of ammonium, sodium, and magnesium nitrates in bulk form. The results demonstrate that, as the standoff distances increases, there is a discernible attenuation in the intensity of the Raman signatures of the nitrates. To discriminate the background lights, improve the signal-to-noise ratio and trigger the weak characteristic bands, Raman spectra were also acquired using higher integration time. For the measurements taken at a 100 meter standoff distances, we were able to achieve a signal-to-noise ratio of about 10. For greater distances, due to the difficulty of locating the target using IR laser, a 50 mW green laser pointer at 485 nm wavelength is used before the IR laser is used for acquiring the Raman signals.

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Raman measurements, using a 785nm laser, are taken of Ammonium Nitrate and Sodium Nitrate buried in sand. Nitrate is kept in clear plastic containers and buried underneath sand at various depths. Raman measurements are then taken at distances of 5m and 20m, with the sand being completely dry as well as completely wet. A different set of experiments was conducted with Nitrate buried in sand in a glass container, where no Raman signal was seen in dry sand. Water was then added at the edge of the container and allowed to migrate to the bottom. Raman measurements are then taken at a distance of 7mm over time to detect Nitrates brought to the surface by water as it wicks to the surface.