Remote Raman spectroscopy of minerals at elevated temperature relevant to Venus exploration

We have used a remote time-resolved telescopic Raman system equipped with 532 nm pulsed laser excitation and a gated intensified CCD (ICCD) detector for measuring Raman spectra of a number of minerals at high temperature to 970 K. Remote Raman measurements were made with samples at 9-meter in side a high-temperature furnace by gating the ICCD detector with 2 micro-sec gate to minimize interference from blackbody emission from mineral surfaces at high temperature as well as interference from ambient light. A comparison of Raman spectra of gypsum (CaSO4.2H2O), dolomite (CaMg(CO3)2), and olivine (Mg2Fe2-xSiO4), as a function of temperature shows that the Raman lines remains sharp and well defined even in the high-temperature spectra. In the case of gypsum, Raman spectral fingerprints of CaSO4.H2O at 518 K were observed due to dehydration of gypsum. In the case of dolomite, partial mineral dissociation was observed at 973 K at ambient pressure indicating that some of the dolomite might survive on Venus surface that is at ~750 K and 92 atmospheric pressure. Time-resolved Raman spectra of low clino-enstatite (MgSiO3) measured at 75 mm from the sample in side the high-temperature furnace also show that the Raman lines remains sharp and well defined in the high temperature spectra. These high-temperature remote Raman spectra of minerals show that time-resolved Raman spectroscopy can be used as a potential tool for exploring Venus surface mineralogy at shorter (75 mm) and long (9 m) distances from the samples both during daytime and nighttime. The remote Raman system could also be used for measuring profiles of molecular species in the dense Venus atmosphere during descent as well as on the surface.

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