Open path FTIR detection of threat chemicals in air and on surfaces

A remote infrared spectroscopy (RIRS) detection system was assembled using a mid infrared (MIR) Fourier Transform interferometer useful in open-path (OP) mode, a reflective infrared telescope and a cryocooled wide band, MCT detector. The system was used for passive mode IR thermal emission measurements and was also coupled to another Newtonian telescope in conjunction with a globar source for active mode measurements. The operation of the system was validated by measuring RIRS spectra of gases (NH 3 ) and condensable vapors: acetone, dichloromethane, methyl ether and acetonitrile. Solid samples were measured by smearing small amounts on aluminum plates after dissolving in appropriate solvents. Highly energetic compounds: TNT, DNT, PETN and RDX were also detected. Experiments of solids on metal surfaces were carried out in passive and active modes. The analyzed samples were placed at different standoff distances up to a maximum of 30 m in active mode and 60 m in passive mode.