Planetary exploration enabled by a compact adaptable, time-resolved, spatial-heterodyne Raman spectrometer

Abstract

Planetary science exploration is transitioning from a focus on remote sensing techniques to in situ instruments for landed missions, and Raman spectrometers are quickly gaining ground as essential to these payloads. To accurately identify targets of interest to planetary science, the Raman spectrometer spectral resolution is required to be better than 0.19 nm. While dispersive spectrometers are a direct way to separate optical radiation into its constituent irradiance spectrum, they have major disadvantage of very inefficient light throughput for high resolution applications because they require very small entrances slits, ~50 μm. This is a major drawback for a stand-off system where target sample illumination size is large and return signals are very weak. Fluorescence is typically brighter than the Raman signal, and in conventional Raman spectroscopy, a slow detector integrates both signals and obscures the Raman signature. To mitigate this, we are developing an ultra-compact, high resolution, high throughput, time-resolved VIS-NIR Raman spatial heterodyne spectrometer (SHS). The SHS replaces the modulation mirror in a high resolution and throughput of a traditional Fourier Transform Spectrometer (FTS) with a stationary grating. The SHS has the same advantage of the FTS, which has two orders of magnitude larger acceptance angle than dispersive spectrometers without sacrificing resolution. In this work we focus on applications to stand-off Raman SHS spectroscopy for the detection of biomarkers and characterization of habitability on planetary surfaces.