A Monolithic Spatial Heterodyne Raman Spectrometer: Initial Tests

• Published in: Applied spectroscopy 2021-01, Vol.75 (1), p.57-69
• Main Authors: Waldron, Abigail, Allen, Ashley, Colón, Arelis, Carter, J. Chance, Angel, S. Michael
• Format: Article
• Language: English
• ISSN: 0003-7028; 1943-3530
• DOI: 10.1177/0003702820936643

A monolithic spatial heterodyne Raman spectrometer (mSHRS) is described, where the optical components of the spectrometer are bonded to make a small, stable, one-piece structure. This builds on previous work, where we described bench top spatial heterodyne Raman spectrometers (SHRS), developed for planetary spacecraft and rovers. The SHRS is based on a fixed grating spatial heterodyne spectrometer (SHS) that offers high spectral resolution and high light throughput in a small footprint. The resolution of the SHS is not dependent on a slit, and high resolution can be realized without using long focal length dispersing optics since it is not a dispersive device. Thus, the SHS can be used as a component in a compact Raman spectrometer with high spectral resolution and a large spectral range using a standard 1024 element charge-coupled device. Since the resolution of the SHRS is not dependent on a long optical path, it is amenable to the use of monolithic construction techniques to make a compact and robust device. In this paper, we describe the use of two different monolithic SHSs (mSHSs), with Littrow wavelengths of 531.6 nm and 541.05 nm, each about 3.5 × 3.5 × 2.5 cm in size and weighing about 80 g, in a Raman spectrometer that provides ∼3500 cm−1 spectral range with 4–5 cm−1 and 8–9 cm−1 resolution, for 600 grooves/mm and 150 grooves/mm grating-based mSHS devices, respectively. In this proof of concept paper, the stability, spectral resolution, spectral range, and signal-to-noise ratio of the mSHRS spectrometers are compared to our bench top SHRS that uses free-standing optics, and signal to noise comparisons are also made to a Kaiser Holospec f/1.8 Raman spectrometer.