Pulsed laser surface fragmentation and mid-infrared laser spectroscopy for remote detection of explosives

Stand-off technology for the remote detection of explosives and their traces on contaminated surfaces is a field of research that has recently gained much interest. Optical methods are well established in applications for counterterrorism because they facilitate analysis without contact between human being and hazardous materials. In this paper, to our knowledge for the first time, a remote stand-off detection system is developed by combination of pulsed laser fragmentation and pulsed mid-infrared laser absorption spectroscopy. Since the absorption of explosives is more efficient for infrared wavelengths laser radiation in the eye safe region around lambda=1.47 mu m rather than the conventional Nd:YAG laser line at lambda=1.06 mu m is preferred for the fragmentation. Generated product gases such as nitric oxide are probed by a synchronized distributed feedback quantum cascade laser (DFB-QCL) at lambda approximate to 5.3 mu m. The ratio of NO and NO2 is a measure to distinguish between energetic and non-energetic materials.