Combined remote LIBS and Raman spectroscopy at 8.6 m of sulfur-containing minerals, and minerals coated with hematite or covered with basaltic dust

Combined remote laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy investigations at a distance of 8.6 m have been carried out in air and under a simulated Martian atmosphere of 933 Pa (7 Torr) CO2 on calcite (CaCO3) gypsum (CaSO4 center dot 2H(2)O), and elemental sulfur (S), and LIBS investigations on chalcopyrite (CuFeS2) and pyrite (FeS2). Both Raman and LIBS techniques have also been used sequentially in air on hematite-coated calcite crystals and on a sample of anhydrite covered with basaltic dust. These experiments demonstrate that by using a frequency-doubled Nd:YAG pulsed laser co-radiating 1064 nm and 532 nm laser beams with a 5 x beam expander, it is possible to measure simultaneously both the Raman and LIBS spectra of calcite, gypsum and elemental sulfur by adjusting the laser power electronically. The spectra of calcite, gypsum, and elemental sulfur contain fingerprint Raman lines; however, it was not possible to measure the remote Raman spectra of pyrite and chalcopyrite because of low intensities of Raman lines. In the cases of CuFeS2, FeS2, and elemental sulfur, S atomic emission lines in the LIBS spectra were detected only in 7 Torr of CO2 pressure and not in air. No S atomic emission lines were detected for gypsum in air or in CO2. In the case of coated/dusted minerals, it was possible to remove the coating or dust with the focused LIBS laser and measure the Raman spectra of subsurface minerals with a 532 nm laser excitation. The complementary nature of these two techniques is highlighted and discussed. (c) 2007 Elsevier B.V. All rights reserved.