Stand-off Raman instrument for detection of bulk organic and inorganic compounds

Abstract

We have designed and tested a portable stand-off gated-Raman system that is capable of detecting organic and inorganic bulk chemicals at stand-off distances to 100 m during day and night time. Utilizing a single 532 nm laser pulse (~25 mJ/pulse), Raman spectra of several organic and inorganic compounds have been measured with the portable Raman instrument at a distance of 10 m in a well-illuminated laboratory. Raman spectra, obtained during a very short period of time (2 micro second), from organic compounds such as acetone, benzene, cyclohexane, 2-propanol, naphthalene, and inorganic nitrates, showed all major bands required for unambiguous chemical identification. We have also measured the Raman spectra of acetone, sulfuric acid, hydrogen peroxide (50%) aqueous solution, nitro-methane containing fuel, and nitrobenzene in glass containers with a 532 nm, 20 Hz pulsed laser excitation and accumulated the spectra with 200 to 600 laser shots (10 to 30 sec integration time) at 100 m with good signal-to-background ratio. The results of these investigations show that the stand-off Raman spectra to 100 m distance can be used to identify Raman fingerprints of both inorganic and organic compounds and could be useful for Homeland security and environmental monitoring.