Standoff Raman Spectroscopy of Explosive Nitrates Using 785 nm Laser

Abstract

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.

Detection of Trace Explosive Materials by Standoff Raman Spectroscopy System

“…The explosive material in C4 is cyclotrimethylenetrinitramine (C 3 H 6 N 6 O 6 ). The spectra detected via standoff Raman spectroscopy coincides well with previously reported literature [16][17][18].…”

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

“…(6) as well as our standoff spectrum coincides well with previously reported literature [8][9][10]. Average difference of peak shift is about 3 cm -1 from that of Sandra Sadate et al [9] and in general the average difference of peak shift is about 2 cm -1 from that of micro Raman spectroscopy. Trinitrotoluene TNT Trinitrotoluene C 7 H 5 (NO 2 ) 3 is another example of an NO 2 containing explosive.…”

Vibrational Spectroscopy of Pain Relievers: Traditional and Remote Raman Techniques

“…In earlier work, the technique has been demonstrated to detect commercially motivated adulteration of extra virgin olive oil with 10 percent canola, grape seed, and sunflower oils, without removing the oil from the container [6]. Using an 11-inches telescope integrated with a 785 nm laser source placed at 250 meters standoff distance from the specimen, Sadate et al, detected nitrates powder [7]. One of the benefits of the remote Raman spectroscopy technique, demonstrated here in the present work, is that it is contactless with the sample, the advantage of collecting the Raman spectra remotely without removing the drug from the containers.…”