Remote Raman spectroscopic study of planetary materials: theory and application based on the SDU-RRS brassboard

Raman spectroscopy has emerged as a crucial mineral analysis technique in planetary exploration missions. Nonetheless, the inherently low Raman scattering efficiency of lunar surface materials makes it challenging to extract sufficient Raman information. Investigating the remote Raman scattering properties of planetary materials is also an urgent requirement for future Raman applications in planetary and lunar explorations. A remote Raman spectrometer, SDU-RRS, was developed to demonstrate the feasibility of lunar remote Raman and to conduct preliminary research on remote Raman scattering properties. The SDU-RRS utilizes a pulsed 532 nm laser, a 100 mm diameter non-focal Cassegrain telescope, a volume phase holographic grating, an intensified charge-coupled device, and the time-gating techniques to achieve Raman detection of weak-signal silicate minerals. The spectral resolution obtained from atomic emission lamps was <4.91 cm-1, and the wavelength accuracy was <1 cm-1, across the spectral range of 120-2430 cm-1. The SDU-RRS is capable of detecting natural augite mixed in a feldspar-olivine-augite matrix at a concentration of 20% under ambient light conditions. In addition, various tests were conducted on geological materials to evaluate the effects of measurement conditions and physical matrix effects, either qualitatively or quantitatively. The transmission of Raman-scattered light was found to be consistent with Lambert's cosine law. A linear correlation was found between Raman intensity and laser power. The effects of grain size, surface roughness, porosity, and shadow-hiding effects were also evaluated. These characteristics are crucial to obtaining conclusive mineralogy in planetary explorations.