Detection of Nitro-aromatic Compound in Soil and Sand using Time Gated Raman Spectroscopy

Laser based time-gated Raman Spectroscopy experiments for detection and identification of nitro-aromatic sample which premixed with soil and sand in different concentrations are conducted. A back-scattered stand-off Raman spectroscopy set-up using a frequency double Nd:YAG pulsed laser (532 nm, 8 ns, 10 Hz) was employed to evaluate samples made up of standard nitro-aromatic compounds, p-nitro Benzoic acid (PNBA) premixed with soil and sand at different concentrations. A sensitive ICCD detector was used to capture the weak Raman signals buried in high background noise at optimised experiments parameters like laser pulse energy, ICCD gate width, background subtraction, number of laser pulses averaging etc. p-nitro benzoic acid up to 5 per cent (v/v) concentration in sand with appreciable signal to noise ratio has been detected. This feasibility study also becomes relevant to evaluate the remnants for post-blast detection of explosives in terrorist attack as most of the explosives used in such attacks contain nitro-aromatic based high energetic explosives.