Pulsed remote Raman system for daytime measurements of mineral spectra

Abstract

A remote Raman system has been developed utilizing a 532 nm pulsed laser and gated intensified charged couple device (ICCD) detector in the oblique geometry. When the system is set for 50 m sample distance it is capable of measuring Raman spectra of minerals located at distances in the range of 10–65 m from the telescope. Both daytime and nighttime operations are feasible and the spectra of minerals can be measured in a short period of time, of the order of a few seconds. In oblique geometry, measured sampling depth is more than 30 m, during which the system maintains very high performance without any adjustments. Much longer sampling depth (0.1–120 m) has been observed when the system is configured in the coaxial geometry. Clear advantages of using a gated detection mode over the continuous (CW) mode of operation in reducing the background signal and eliminating long-lived fluorescence signals from the Raman spectra are presented. The performance of the pulsed Raman system is demonstrated by measuring spectra of Raman standards including benzene (C 6H 6) and naphthalene (C 10H 8), a low Raman cross section silicate mineral muscovite (KAl 2(Si 3Al)O 10(OH) 2), and a medium Raman cross section mineral calcite (CaCO 3).