Remote Raman Sensing Using a Single-Grating Monolithic Spatial Heterodyne Raman Spectrometer: A Potential Tool for Planetary Exploration

Evan M Kelly; Miles J Egan; Arelis Colόn; S Michael Angel; Shiv K Sharma

doi:10.1177/00037028221121304

Remote Raman Sensing Using a Single-Grating Monolithic Spatial Heterodyne Raman Spectrometer: A Potential Tool for Planetary Exploration

Appl Spectrosc. 2023 May;77(5):534-549. doi: 10.1177/00037028221121304. Epub 2022 Oct 12.

Authors

Evan M Kelly¹, Miles J Egan¹, Arelis Colόn², S Michael Angel², Shiv K Sharma¹

Affiliations

¹ Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, HI, USA.
² Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC, USA.

PMID: 36223496
DOI: 10.1177/00037028221121304

Abstract

Advances in Raman instrumentation have led to the implementation of a remote dispersive Raman spectrometer on the Perseverance rover on Mars, which is used for remote sensing. For remote applications, dispersive spectrometers suffer from a few setbacks such as relatively larger sizes, low light throughput, limited spectral ranges, relatively low resolutions for small devices, and high sensitivity to misalignment. A spatial heterodyne Raman spectrometer (SHRS), which is a fixed grating interferometer, helps overcome some of these problems. Most SHRS devices that have been described use two fixed diffraction gratings, but a variance of the SHRS called the one-grating SHRS (1g-SHRS) replaces one of the gratings with a mirror, which makes it more compact. In a recent paper we described monolithic two-gratings SHRS, and in this paper, we investigate a single-grating monolithic SHRS (1g-mSHRS), which combines the 1g-SHRS with a monolithic setup previously tested at the University of South Carolina. This setup integrates the beamsplitter, grating, and mirror into a single monolithic device. This reduces the number of adjustable components, allows for easier alignment, and reduces the footprint of the device (35 × 35 × 25 mm with a weight of 80 g). This instrument provides a high spectral resolution (∼9 cm^-1) and large spectral range (7327 cm^-1) while decreasing the sensitivity to alignment with a field of view of 5.61 mm at 3m. We discuss the characteristics of the 1g-mSHRS by measuring the time-resolved remote Raman spectra of a few inorganic salts, organics, and minerals at 3 m. The 1g-mSHRS makes a good candidate for planetary exploration because of its large spectral range, greater sensitivity, competitively higher spectral resolution, low alignment sensitivity, and high light throughput in a compact easily aligned system with no moving parts.

Keywords: 1g-mSHRS; S/N; SHRS; Spatial heterodyne Raman spectrometer; minerals; organic compounds; remote Raman sensing; signal-to-noise ratio; single-grating monolithic spatial heterodyne spectrometer.