New Raman Spectrometer Paves the Way for Lunar and Planetary Exploration

Raman spectroscopy has been one of the major spectroscopic techniques used in mineral analysis applications. As a result, Raman spectroscopy has been used in research projects that study other planets, including Mars. Recently, a team of researchers from Shandong University and the Chinese Academy of Sciences developed and tested a new remote Raman spectrometer designed to improve mineral analysis in planetary exploration. Published in the journal Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, the study’s findings show how this new Raman spectrometer, titled the Shandong University Remote Raman Spectrometer (SDU-RRS), can detect weak Raman signals from silicate minerals (1).

Raman spectroscopy has long been recognized as a powerful tool for mineral analysis in planetary surface exploration (2,3). However, Raman spectroscopy has encountered obstacles in analyzing silicate minerals in the past because of low Raman scattering efficiency (1). The SDU-RRS was specifically designed to address these challenges and advance the development of remote Raman technology for future space missions.

In the study, the researchers explain that their SDU-RRS has several functionalities that other Raman spectrometers do not possess. Several of these components in the SDU-RRS system include a pulsed 532-nm laser, a non-focal Cassegrain telescope, a volume phase holographic grating, and an intensified charge-coupled device (ICCD) (1). The SDU-RRS also employs a time-gating technique, which significantly improves the ability to detect weak Raman signals from planetary minerals by suppressing background noise and stray light (1).

The researchers demonstrated in the study that their SDU-RRS has a spectral range of 241–2430 cm⁻¹. Experimental testing demonstrated that the SDU-RRS can detect augite within a feldspar-olivine-augite matrix at a concentration of 20% from approximately one meter under ambient lighting conditions (1).

In their experiment, the researchers used different environmental and physical factors to test how strong the Raman signal acquisition was. They found that the Raman-scattered light follows Lambert’s cosine law, meaning that the intensity of scattered light varies predictably with the angle of incidence (1). Additionally, a direct linear relationship was established between Raman intensity and laser power, which provides crucial insights for optimizing remote Raman detection strategies (1).

Part of the experimental procedure also examined how the Raman signal acquisition was influenced by porosity, grain size, surface roughness, and shadowing effects. The results show that smaller grain sizes lead to broader and weaker Raman peaks, making mineral identification more challenging (1). Increased surface roughness and porosity also contributed to reductions in Raman signal intensity (1).

The study also determined the detection limits of the SDU-RRS, establishing that it can identify olivine at concentrations of 15% or higher and augite at concentrations of 20% or higher when dealing with fine-grained samples (<38 μm) (1).

The development of the SDU-RRS is particularly significant for upcoming planetary missions, including China’s Chang’e-7 (CE-7) lunar exploration program. As part of pre-research for the CE-7 mission, the SDU-RRS was designed to detect silicate minerals such as pyroxene with high precision (1).

Moving forward, it is expected that the information obtained from this study will influence the design and functionality of Raman spectrometers for planetary missions. By enhancing the ability to detect and characterize minerals remotely, this technology could play a vital role in identifying key geological and geochemical features on the Moon, Mars, and other celestial bodies (1).

Raman spectroscopy has helped characterize minerals such as olivine, quartz, mica, gypsum, and potassium feldspar (2). It is anticipated that as Raman spectrometer technology improves, the more minerals will be discovered and classified. As future missions continue to learn more about Mars and other planetary bodies, Raman spectroscopy will undoubtedly play a role in advancing our understanding of extraterrestrial mineralogy. An excellent resource for studying infrared and Raman spectra of inorganic compounds is found in reference (4).

References

1. Qi, X.; Liu, P.; Qu, H.; et al. Design and Development of a Stand-off Raman Brassboard (SDU-RRS) for the Spectroscopic Study of Planetary Materials. Spectrochimica Acta Part A: Mol. Biomol. Spectrosc. 2025, 325, 125026. DOI: 10.1016/j.saa.2024.125026
2. Wetzel, W. Autonomous Mineral Classification Enhances Planetary Exploration. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/autonomous-mineral-classification-enhances-planetary-exploration (accessed 2025-02-12).
3. Wetzel, W. UV Radiation Impact on Raman and Infrared Signals: A Look at the Surface of Mars. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/uv-radiation-impact-on-raman-and-infrared-signals-a-look-at-the-surface-of-mars (accessed 2025-02-12).
4. Nyquist, R. A.; Kagel, R. O.; Putzig, C. L.; Leugers, M. A. Handbook of Infrared and Raman Spectra of Inorganic Compounds and Organic Salts; 4 Vols.; 1st ed.; Academic Press: 1996; ISBN 978-0125234443.