Standoff Detection of High Explosive Materials at 50 Meters in Ambient Light Conditions Using a Small Raman Instrument

Abstract

We have designed and demonstrated a standoff Raman system for detecting high explosive materials at distances up to 50 meters in ambient light conditions. In the system, light is collected using an 8-in. Schmidt-Cassegrain telescope fiber-coupled to an f/1.8 spectrograph with a gated intensified charge-coupled device (ICCD) detector. A frequency-doubled Nd : YAG (532 nm) pulsed (10 Hz) laser is used as the excitation source for measuring remote spectra of samples containing up to 8% explosive materials. The explosives RDX, TNT, and PETN as well as nitrate- and chlorate-containing materials were used to evaluate the performance of the system with samples placed at distances of 27 and 50 meters. Laser power studies were performed to determine the effects of laser heating and photodegradation on the samples. Raman signal levels were found to increase linearly with increasing laser energy up to approximately 3 x 10(6) W/cm2 for all samples except TNT, which showed some evidence of photo- or thermal degradation at higher laser power densities. Detector gate width studies showed that Raman spectra could be acquired in high levels of ambient light using a 10 microsecond gate width.

The application of single particle aerosol mass spectrometry for the detection and identification of high explosives and chemical warfare agents

“…6 These systems focus on detecting the actual explosive device by visual characteristics such as the shape of the explosive material or detonator. 7 Other bulk detection techniques rely on the chemical structure of the explosive, such as molecular bending or twisting in terahertz (THz) spectroscopy and Raman spectroscopy, 7,8,9 and the molecular electric field gradients in nuclear quadrupole resonance (NQR).…”

“…8 Raman spectroscopy has even been applied to the standoff detection of high explosives in a silica matrix from up to 50 m away. 9 NQR detection has also been modified for standoff detection by adapting the receiving and transmitting coils and using a narrow bandwidth for detection. 11 The main disadvantage of bulk detection systems is the significant amount of explosive necessary to trigger an alarm (e.g.…”

Remote Raman Spectroscopy for Planetary Exploration: A Review

“…Utilizing a pulsed laser with a gated ICCD detector offers the potential to make time-resolved measurements in addition to ambient measurements. 28 This approach can allow avoidance of fluorescence in luminescent minerals 35 or the creation of a combined Raman/laser-induced fluorescence (LIF) instrument that is capable of greater accuracy in the identification of an unknown sample. 3 Sharma has reported that a typical gate delay of 10 ns is needed to collect Raman without fluorescent interference in a Raman/LIF system.…”

“…27 Carter et al have reported standoff detection of high explosive materials at 50 meters in ambient light conditions using a small Raman instrument. 28 Sharma et al measured remote Raman spectra of minerals and organic compounds to 100 m. laser pulse at a distance of 213 m. 30 Using semi-portable equipment, Wu et al have reported on Raman spectroscopic identification of man-made organic compounds at distances of over half a kilometer. 31 A remote Raman system with Raman imaging capability has potential for determining mineral distribution and composition on a rock surface by comparing a set of Raman images collected for various minerals.…”

Experimental Evaluation of the UV Raman Lidar Sensitivity in Detection of Traces of Chemical Compounds

“…At the same time, the effect of Raman scattering allows to detect and identify substances not only in the gaseous phase, but also in the liquid and solid phases. Solution of the problem of development of the lidar method for the remote detection and identification of traces of chemical compounds on the surfaces of various items is of great practical and scientific interest and should be studied to assess its sensitivity, noise-stability, and the application field [3][4][5]. For this purpose, the work was done to upgrade and use the Raman-lidar method for the detection of traces of high-energy nitrogen-containing chemical compounds on the surface.…”