Galán Freyle, Nataly Y.

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    Standoff laser-Induced thermal emission of explosives
    (2013) Galán Freyle, Nataly Y.; Hernández Rivera, Samuel P.; College of Arts and Sciences - Sciences; Mina Camilde, Nairmen; Vega, Carmen A.; Department of Chemistry; Ortiz, Juan A.
    A laser mediated methodology for remote thermal excitation of analytes followed by standoff infrared (IR) detection is proposed. The goal of this study was to determine the feasibility of using laser induced thermal emission (LITE) to vibrationally excite explosives residues deposited on surface to detect the compounds remotely. Telescope based Fourier Transform IR (FT-IR) spectral measurements were carried out to examine substrates containing trace amounts of threat compounds used in explosive devices. Highly energetic materials (HEM) used as targets were pentaerythritol tetranitrate (PETN), triacetone triperoxide (TATP), 1,3,5- trinitroperhydro-1,3,5-triazine (RDX), 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT) and ammonium nitrate (AN) at concentrations from 5 to 200 μg/cm2 . Target substrates of various thicknesses were remotely heated using a high power CO2 laser, and their mid-IR (MIR) thermally stimulated emission spectra were recorded. The telescope was configured from reflective optical elements in order to minimize emission losses in the MIR frequencies and to provide optimum overall performance. Spectral replicas were acquired at distances from 4 to 64 m with an FT-IR interferometer at 4 cm-1 resolution and 10 scans. Laser power was varied from 4-36 W at radiation exposure times of 10, 20, 30 and 60 s. CO2 laser powers were adjusted to improve the detection and identification of the HEM samples. The advantages of increasing the thermal emission were easily observed in the results. Signal intensities were proportional to the thickness of the coated surface (a function of the surface concentration), as well as the laser power and laser exposure time. The limits of detection for the different explosive were from 21 to 1 μg/cm2 at 4 m. The detection was possible at 64 m for 200 μg/cm2 of RDX.