Remote Raman sensor system for testing of rocks and minerals

Recent and future explorations of Mars and lunar surfaces through rovers and landers have spawned great interest in developing an instrument that can perform in-situ analysis of minerals on planetary surfaces. Several research groups have anticipated that for such analysis, Raman spectroscopy is the best suited technique because it can unambiguously provide the composition and structure of a material. A remote pulsed Raman spectroscopy system for analyzing minerals was demonstrated at NASA Langley Research Center in collaboration with the University of Hawaii. This system utilizes a 532 nm pulsed laser as an excitation wavelength, and a telescope with a 4-inch aperture for collecting backscattered radiation. A spectrograph equipped with a super notch filter for attenuating Rayleigh scattering is used to analyze the scattered signal. To form the Raman spectrum, the spectrograph utilizes a holographic transmission grating that simultaneously disperses two spectral tracks on the detector for increased spectral range. The spectrum is recorded on an intensified charge-coupled device (ICCD) camera system, which provides high gain to allow detection of inherently weak Stokes lines. To evaluate the performance of the system, Raman standards such as calcite and naphthalene are analyzed. Several sets of rock and gemstone samples obtained from Ward’s Natural Science are tested using the Raman spectroscopy system. In addition, Raman spectra of combustible substances such acetone and isopropanol are also obtained. Results obtained from those samples and combustible substances are presented.