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Stand-off Detection of Chemicals by UV Raman Spectroscopy

Volume 54, Number 6 (June 2000) Page 800-806

Wu, Ming; Ray, Mark; Fung, K. Hang; Ruckman, Mark W.; Harder, David; Sedlacek, Arthur J.

Experimental results are reported on a mobile, stand-alone, solarblind ultraviolet (UV) Raman lidar system for the stand-off detection and identification of liquid and solid targets at ranges of hundreds of meters. The lidar is a coaxial system capable of performing rangeresolved measurements of gases and aerosols, as well as solids and liquids. The transmitter is a flash lamp pumped 30 Hz Nd:YAG laser with quadrupled output at 266 nm. The receiver 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) detector. The rejection of elastic light scattering by the edge filter is better than one part in 105, while the transmittance 500 cm-1 to the red of the laser line is greater than 50%. Raman data are shown for selected solids, 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 ~500 g/m2 for liquid spills of common solvents at the range of one half of a kilometer is possible.