Remote-Raman Spectroscopy at Intermediate Ranges Using Low-Power cw Lasers

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Abstract
A portable Raman system is described that has been developed for line-of-site spectral measurements of remotely located samples at intermediate ranges. Raman spectra were measured at distances up to 20 m with the use of a 40-mm-diameter collection optic ( f/500) and at 16.7 m with a 22-mm-diameter collection optic ( f/750). In all cases, low-power cw lasers were used with powers ranging from 23 to 100 mW. The system consists of a small f/4 image-corrected spectrograph with a liquid-nitrogen-cooled CCD detector and has been demonstrated with both an argon-ion laser, emitting at 488 nm, and an 809-nm diode laser. Applications of the system include monitoring of organic and inorganic compounds at toxic waste sites during remediation, process monitoring, and remote detection of highly toxic materials.