This paper from Blacksberg et al. at JPL explores the use of picosecond Raman spectroscopy, with a gated detector, for mineral characterization on the Martian surface. Huge strides have been made in portable spectroscopy over the past 20 years, both in elemental (X-ray fluorescence and laser-induced breakdown spectroscopy) and molecular (UV-visible, near-infrared, mid-infrared, and Raman) instrumentation. The developers of those commercial instruments have paid great attention to their size, weight, and power (SWaP) requirements, as well as physical ruggedness and ability to work in varying ambient conditions in the field. However, the greatest challenge is in operating spectrometers in space, or on the lunar or Martian surface. Landmark instrumentation includes a gas chromatograph-mass spectrometer (GC-MS) in a Viking probe to Mars, and an FT-IR spectrometer on Voyager to Jupiter. This paper explores the particular challenge of Raman spectroscopy for a Mars rover, given that detection and characterization of both the minerals and low concentration organic compounds is essential. As well as stand-off capability, this Raman instrument needs to overcome the well-known problems of fluorescence (very common in minerals due to rare earth and transition metal ions) and sample burning, while collecting adequate signal-to-noise spectra in a reasonable time, permitting efficient mapping of a sample. The approach explored is using a time-gated single photon avalanche diode (SPAD) array, in conjunction with a newly developed high-speed microchip laser. The laser, after doubling, produces 532 nm excitation, with 100 ps width pulses and a repetition rate of up to 500 kHz. This paper presents a careful examination of the challenges, and provides a roadmap to their solution.
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