A compact laser spectrometer for the detection of explosives from a safe spot is presented. This laser setup also opens the possibility for the trace detection of explosives.Laser-Stand-off technology for remote detection of explosives and their traces on contaminated surfaces is a field of research that has recently gained much interest. In this report, to our knowledge for the first time, a remote compact stand-off detection system is presented that uses pulsed mid infrared laser absorption spectroscopy, if necessary in combination with pulsed laser fragmentation (PLF). A compact fiber coupled system is developed in the so called "eye-safe" region. Here we introduce a compact fiber coupled sensor containing a fiber amplifier for the fragmentation and a Quantum Cascade Laser (QCL) operating in the mid-infrared for the absorption spectroscopy of the product gases from different traces of explosives like TNT and HMX. Figure 1 shows a typical absorption spectrum of nitric oxide (NO) produced by photo fragmentation of HMX. Fig. 1: NO spectrum after PLF of HMX.Experimental investigations indicate that the absorption of explosives is more efficient in the "eye-safe" spectral range around 1.5 μm rather than for the conventionally used fundamental Nd:YAG line at 1.06 μm [1]. In order to optimize laser material interaction with a compact setup a laser excitation in the "eye-safe" region is done by an Er:Yb co-doped fiber-amplifier. In our setup an Er:Yb-doped glass passively Q-switched diode-pumped solid state laser (DPSSL) emitting around 1535 nm is amplified by an Erbium-Ytterbium co-doped large mode area fiber and generates pulses with energies up to E P = 200 μJ at a high repetition rate in the kHz regime. QCLs at different operating wavelengths are tested in cw-mode and in pulsed mode for best performance for the detection of hazardous materials. First results for the detection of TATP which is present in the gas phase without pre-treatment are also discussed.[1] C.Bauer, P.Geiser, J.Burgmeier, G.Holl and W.Schade, "Pulsed laser surface fragmentation and mid-infrared laser spectroscopy for remote detetction of explosives", Applied Physics B 85, 251-256 (2006).
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