Mid-Infrared Lidar for Remote Detection of Explosives

Laser ablation spectroscopy combining with high-resolution midinfrared absorption measurements offers interesting possibilities for sensitive and selective stand-off analysis of surface contaminations under real-time operation conditions. The detection of NO_x production rates emitted from surfaces after interaction with a pulsed infrared laser beam allows distinguishing between different surface contaminations, e.g. energetic and non-energetic materials but also between molecules with similar atomic composition. This is shown for the explosives TNT, Octol and HMX. For efficient laser fragmentation of surface contaminations the excitation wavelengths 1.06 μm and 1.47 μm are compared indicating that a pulse power as low as 0.25 mJ/pulse at 1.47 μm is sufficient for laser-induced surface evaporation of explosive contaminations. Then no plasma is ignited by the infrared laser pulses and therefore the obtained NO_x emission is only due to the explosive surface contamination.