New Auto-Focusing Raman Spectrometer Enhances Deep Space Exploration

One of the more recent developments of scientific instrumentation was a cutting-edge, auto-focusing Raman spectrometer that improves the accuracy and efficiency of planetary material analysis, according to a recent study published in Remote Sensing (1).

Raman spectrometers, known for their ability to identify molecular compositions by scattering laser light, have become indispensable tools in space exploration. NASA has already deployed two such instruments, SuperCam and SHERLOC, aboard the Perseverance Rover in the Mars 2020 mission (1,2). However, during ground tests, the SHERLOC team identified an axial offset (~720 μm) between its Autofocus Context Imager (ACI) and the spectrometer focus (1). This discrepancy necessitated a correction to avoid compromising the Raman intensity.

Planet Mars, in red rusty color, on a dark background. Elements of this image were furnished by NASA | Image Credit: © Artsiom P - stock.adobe.com

Chinese researchers Zongcheng Ling and Yiheng Liu, along with their team, explored this issue. They recently demonstrated in their study an auto-focusing Raman spectrometer that can improve accuracy and efficiency of planetary material analysis, with the hope that their technology could potentially be used in future space missions.

Ling and Liu and their team first sought to streamline the application of Raman instruments in deep space. Knowing the difficulties and limitations of previous instrumentation used in deep space, the researchers proposed an automatic focusing method that optimizes Raman signals during spectrum collection. This novel method evaluated focus conditions numerically and searched for the extremum point (the location on the sample where the Raman signal is either maximized or minimized) to determine the final focal point (1). This approach eliminated the need for a confocal imager or laser ranger, making the system more compact and suitable for miniaturized payloads, which is perfect for space missions (1).

To demonstrate that their method is effective, the researchers developed an Auto-focus Raman Probe (SDU-ARP) in their laboratory. The auto-focusing technique, which enables the SDU-ARP to focus in as little as 20 seconds with an error margin of less than 0.2 mm, significantly enhances the signal-to-noise ratio (S/N) of Raman spectra (1). Performance tests confirmed the method’s utility, where the SDU-ARP was subjected to testing organic and inorganic materials and did so successfully (1).

One of the major advantages of this automatic focusing strategy is its ability to minimize human error and improve the reliability of intensity comparisons between different samples (1). This capability is particularly beneficial in scenarios where spectrometers cannot focus using other criteria, such as in low-light conditions or on lightweight bodies like asteroids.

The researchers' work represents a significant advancement in the field, providing a robust, intelligent, and low-redundancy solution for Raman signal acquisition. The SDU-ARP’s ability to operate efficiently in challenging environments, such as the permanently shadowed regions of the Lunar south pole, makes it a promising candidate for future space missions (1).

Moreover, the implementation of this auto-focusing method addresses the high-computing cost issue often associated with traditional focusing techniques (1). By reducing the need for multiple acquisitions during the focusing procedure, the system enhances the efficiency and effectiveness of data collection, paving the way for more streamlined and cost-effective deep space exploration missions (1).

The integration of the auto-focusing method into a prototype system also demonstrates its practical applicability in laboratory settings for further research on planetary materials. This advancement not only enhances the capabilities of Raman spectrometers, but it also broadens the scope of their application in space exploration, enabling more detailed and accurate analysis of extraterrestrial surfaces.

References

(1) Liu, Y.; Liu, C.; Xin, Y.; et al. A Signal-Based Auto-Focusing Method Available for Raman Spectroscopy Acquisitions in Deep Space Exploration. Remote Sens. 2024, 16 (5), 820. DOI: 10.3390/rs16050820

(2) Clave, E.; Beyssac, O.; Bernard, S.; et al. Radiation-Induced Alteration of Apatite on the Surface of Mars: First In Situ Observations with SuperCam Raman Onboard Perseverance. Sci. Rep. 2024, 14, 11284. DOI: 10.1038/s41598-024-61494-5