Standoff raman spectroscopy system for detection of explosives, chemical warfare agents simulants and toxic industrial compounds

Abstract

In this work a remote Raman system has been designed, assembled and tested for detecting explosives, Toxic Industrial Compounds (TIC) and Chemical Warfare Agents Simulants (CWAS) at laboratory scale up to 7 m target-telescope distance. The prototype system consists of a Renishaw Raman Microspectrometer, model RM2000, equipped with a charge-coupled device (CCD) detector, a telescope, a fiber optic assembly and a single wavelength/frequency laser source (514/488 nm and 532 nm). The telescope was coupled to the Raman microscope using an optical fiber and filters for rejection of laser radiation and Rayleigh scattering. Two convex lenses collimate the light from the telescope output, which is directed into the fiber optic from which the focusing objective was removed. The output of the fiber was directly coupled to the Raman system by a 5x objective. To test the standoff sensing system, the VIS Raman Telescope was used in detection of secondary explosives: 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (2,4- DNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), triacetone triperoxide (TATP) and plastic explosive C4, with detection limits below 10 mg. The TICs used were benzene, toluene, xylenes, chloroform, CCl4 and CS2. Other compounds studied were Chemical Warfare Agents Simulants dimethylmethyl phosphonate (DMMP), 2-chloroethyl ethyl sulfide (2-CEES). Solid samples (explosives) were deposited on stainless steel plates and liquid samples were transferred into 5 mL glass vials. Both types of samples were placed at a distance of 7 m from the telescope. Raman spectra of compounds were acquired in the Raman shift range of 100-3200 cm-1 using laser powers varying from 50 mW to 1 W and integration times of 1 to 30 s.

En este trabajo se diseñó un sistema de detección remota Raman, el cual se utilizó en la detección de explosivos, simulantes de agentes de guerra químicos y compuestos tóxicos industriales a una distancia del telescopio-muestra de 7 m. El diseño consiste de un microespectrómetro Raman Renishaw modelo RM2000 equipado con un detector CCD, un telescopio, una fibra óptica y una fuente de láser (514/488 nm o 532 nm). El telescopio se acopló al microscopio Raman por medio de una fibra óptica. Dos lentes convexos coliman la luz proveniente de la salida del telescopio, la cual converge directamente sobre la fibra óptica, la salida de la fibra se acopló al sistema Raman mediante un objetivo de 5x. El sistema de detección remota se verificó utilizando explosivos secundarios: TNT, 2,4-DNT, RDX, TATP y el explosivo plástico C4, con limites de detección por debajo de 10 mg. Los compuestos tóxicos industriales empleados fueron benceno, tolueno, xylenos, cloroformo, CCl4 y CS2. Otros compuestos estudiados fueron los simulantes de agentes de guerra químicos: dimetilmetilfosfonato (DMMP) y 2-cloroetiletilsulfuro (2-CEES). Las muestras solidas se depositaron sobre láminas de acero inoxidable y las muestras líquidas se transfirieron a frascos de 5 mL. Ambos tipos de muestras se colocaron a una distancia de 7 m del telescopio. Los espectros de los compuestos se adquirieron en el rango de dispersión Raman de 100-3200 cm-1 utilizando potencias del láser de 50 mW a 1 W y tiempos de integración de 1 a 30 s.