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7 October 2014 A picosecond laser FAIMS analyzer for detecting ultralow quantities of explosives
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A method for detecting ultralow quantities of explosives in air and explosive traces using a state-of-the-art picosecond chip Nd3+:YAG laser has been elaborated. The method combines field asymmetric ion mobility spectrometry (FAIMS) with laser ionization of air samples and laser desorption of analyzed molecules from examined surfaces. Radiation of the fourth harmonic (λ = 266 nm, τpulse = 300 ps, Epulse = 20-150 μJ, ν = 20-300 Hz) was used. The ionization efficiencies for trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX), and glyceryl trinitrate (NG) were investigated. The dependences on frequency, pulse energy, peak intensity, and average power for TNT and RDX were determined. It was shown that the optimal peak intensity should be no less than 2∙106 W/cm2; at lower peak intensities, the increase of the average laser power in the interval 5–15 mW enhanced the ion signal. The results of detection of TNT, RDX, and NG vapors under these conditions were compared with the results obtained using nanosecond laser excitation. The detected ion signals for all explosives were shown to be two- to threefold higher in the case of picosecond excitation. The FAIMS laser desorption regime was developed where a laser beam exiting the detector after removal of a special plug was used. The results of TNT and RDX detection are presented. The chip Nd3+:YAG laser has a small emitter and a consumed electric power of 25 W. The estimated detection threshold of the prototype picosecond laser FAIMS analyzer of explosives is (1-3)∙10-15g/cm3 for TNT vapors.
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Alexander A. Chistyakov, Gennadii E. Kotkovskii, Alexey V. Sychev, Ivan P. Odulo, Artem S. Bogdanov, Anatoly N. Perederiy, Evgeny M. Spitsyn, and Alexander V. Shestakov "A picosecond laser FAIMS analyzer for detecting ultralow quantities of explosives", Proc. SPIE 9253, Optics and Photonics for Counterterrorism, Crime Fighting, and Defence X; and Optical Materials and Biomaterials in Security and Defence Systems Technology XI, 925302 (7 October 2014);

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