Stand-off detection of chemicals by UV Raman spectroscopy

Experimental results are reported on a mobile, stand-alone, solar-blind ult raviolet (UV) Raman lidar system for the stand-off detection and identifica tion of liquid and solid targets at ranges of hundreds of meters. The lidar is a coaxial system capable of performing range-resolved measurements of g ases and aerosols, as well as solids and liquids. The transmitter is a flas h lamp pumped 30 Hz Nd:YAG laser with quadrupled output at 266 nm. The rece iver subsystem is comprised of a 40 cm Cassegrain telescope, a holographic UV edge filter for suppressing the elastic channel, a 0.46 m Czerny-Turner spectrometer, and a time gated intensified charge-coupled device (CCD) dete ctor. The rejection of elastic light scattering by the edge filter is bette r than one part in 10(5), while the transmittance 500 cm(-1) to the red of the laser line is greater than 50%. Raman data are shown for selected solid s, neat liquids, and mixtures down to the level of 1% volume ratio. On the basis of the strength of the Raman returns, a stand-off detection limit of similar to 500 g/m(2) for liquid spills of common solvents at the range of one half of a kilometer is possible.