The evaluation of time‐resolved Raman spectroscopy for the suppression of background fluorescence from space‐relevant samples

Abstract

One of the primary goals in space research is the search for signs of extant or extinct extraterrestrial life, and Raman spectroscopy can play a role in this field. Raman spectrometers are planned for future missions to Mars and possibly the Moon to identify the mineralogical surface composition and potentially existing organic compounds (especially on Mars). However, a major challenge in Raman spectroscopy, especially in the visible range, is the strong fluorescence background. Time‐resolved Raman spectroscopy (TRRS) can provide selective detection of Raman signals over the generally longer living fluorescence. This study investigates the potential of a TRRS system, using 3‐ps, 440‐nm laser pulses and time‐gated detection with an intensified charge‐coupled device (CCD) camera. Test samples were the lichen Xanthoria elegans as an extraterrestrial life analogue, and a lunar regolith analogue material (LRS) as a planetary surface analogue. The TRRS technique is evaluated by comparing gated to nongated Raman spectroscopy using different detectors but with otherwise the same instrument and identical measurement conditions. The gated spectra of X. elegans showed significant signal‐to‐noise ratio (SNR) improvements compared to the nongated spectra. The visible Raman lines could be assigned to the photoprotective pigment parietin. For the LRS sample, measurement spots with a good SNR in the nongated spectrum were not significantly improved by measuring in gated mode. However, spots dominated by fluorescence showed significant improvement in gated mode because of fluorescence suppression. Minerals such as plagioclase, diopside, olivine, apatite, and a carbonate mineral were detected. In most cases, TRRS provided better results compared to nongated measurements, demonstrating the suitability for future space‐exploration missions.