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Published September 10, 2010 | Published
Journal Article Open

Time-resolved Raman spectroscopy for in situ planetary mineralogy

Abstract

Planetary mineralogy can be revealed through a variety of remote sensing and in situ investigations that precede any plans for eventual sample return. We briefly review those techniques and focus on the capabilities for on-surface in situ examination of Mars, Venus, the Moon, asteroids, and other bodies. Over the past decade, Raman spectroscopy has continued to develop as a prime candidate for the next generation of in situ planetary instruments, as it provides definitive structural and compositional information of minerals in their natural geological context. Traditional continuous-wave Raman spectroscopy using a green laser suffers from fluorescence interference, which can be large (sometimes saturating the detector), particularly in altered minerals, which are of the greatest geophysical interest. Taking advantage of the fact that fluorescence occurs at a later time than the instantaneous Raman signal, we have developed a time-resolved Raman spectrometer that uses a streak camera and pulsed miniature microchip laser to provide picosecond time resolution. Our ability to observe the complete time evolution of Raman and fluorescence spectra in minerals makes this technique ideal for exploration of diverse planetary environments, some of which are expected to contain strong, if not overwhelming, fluorescence signatures. We discuss performance capability and present time-resolved pulsed Raman spectra collected from several highly fluorescent and Mars-relevant minerals. In particular, we have found that conventional Raman spectra from fine grained clays, sulfates, and phosphates exhibited large fluorescent signatures, but high quality spectra could be obtained using our time-resolved approach.

Additional Information

© 2010 Optical Society of America. Received 12 April 2010; revised 20 July 2010; accepted 12 August 2010; posted 13 August 2010 (Doc. ID 126635); published 8 September 2010. We acknowledge invaluable discussions on Mars 2018 with Sabrina Feldman at the Jet Propulsion Laboratory (JPL). The research described in this publication was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (NASA). Continuous-wave Raman measurements were performed at the Mineral Spectroscopy Laboratory in the Department of Geological and Planetary Sciences at the California Institute of Technology, and time-resolved experiments at the JPL.

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