Stand-Off Detection of DNT Isomers by Raman Spectroscopy with Nanosecond Time-Gating

Abstract

AbstractA mobile platform-based stand-off detection system for chemicals and explosive materials, based on Raman Spectroscopy with nanosecond time-gating was tested for isomers identifications located up to a distance of 30 m. Laser based nanosecond time-gated Raman Spectroscopy experiments were conducted for detection and identification of isomers of Di-nitrotoluene (DNT) at a standoff distance of up to 30 m. A back-scattered stand-off Raman spectroscopy set-up using a nano-second pulsed laser, receiving telescope and ICCD (Intensified Charge Couple Device) coupled spectrograph was employed to detect and identify the samples. The second harmonic of Nd:YAG laser at 532 nm wavelength:, 4 ns Pulse duration, & 10 Hz Rep Rate was used as an excitation source. ICCD coupled Spectrometer with reflection telescope were used to collect and record the weak Raman signals. Standoff experiments for isomers identification were carried out with different number of accumulations and gratings (300lines/mm and 1800 lines/mm grating) to achieve Raman spectra at different resolutions. Isomer samples 2,4- DNT and 2,6- DNT and their mixtures were recorded for identification with appreciable signal to noise ratio. 2,4 and 2,6 DNT were mixed in 50:50 ratio and identified from up to 30 m. Thus Time Gated Raman spectroscopy is an reliable method for identification & distinguishing chemical samples and isomers in mixture form.KeywordsTime gated Raman spectroscopyStandoff detectionIsomer IdentificationDi-nitrotoluene