Remote Pulsed Raman Spectroscopy of Inorganic and Organic Materials to a Radial Distance of 100 Meters

Abstract

A portable pulsed remote Raman spectroscopy system has been fabricated and tested to 100 m radial distance. The remote Raman system is based on a directly coupled f/2.2 spectrograph with a small (125 mm diameter) telescope and a frequency-doubled Nd:YAG pulsed laser (20 Hz, 532 nm, 25 mJ/pulse) used as the excitation source in a co-axial geometry. The performance of the Raman system is demonstrated by measuring the gated Raman spectra of calcite, sodium phosphate, acetone, and naphthalene. Raman spectra of these materials were recorded with the 532 nm pulsed laser excitation and accumulating the spectra with 600 laser shots (30 s integration time) at 100 m with good signal-to-background ratio. The remote pulsed Raman system can be used for remotely identifying both inorganic and organic materials during daytime or nighttime. The system will be useful for terrestrial applications such as monitoring environmental pollution and for detecting minerals and organic materials such as polycyclic aromatic hydrocarbons (PAHs) on planetary surfaces such as Mars.