SHERLOC's Precision Unveiled: Calibration Method Enhances Raman Spectroscopy on Mars

A recent study published in Applied Spectroscopy presents a simple yet robust method for enhancing the precision of Raman spectroscopy measurements conducted by the SHERLOC instrument on NASA's Perseverance rover (1). The study, titled "Calibration of Raman Bandwidths on the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) Deep Ultraviolet Raman and Fluorescence Instrument Aboard the Perseverance Rover," was conducted by lead author Ryan S. Jakubek and his team at the NASA Johnson Space Center, in Houston, Texas, and it provides a solution to an important challenge spectroscopists face when trying to accurately calibrate Raman spectral bandwidths (1).

Sunset on Mars. Mars mountains, view from the valley | Image Credit: © Peter Jurik - stock.adobe.com

These spectral bandwidths, which are influenced by both intrinsic Raman bands (IRB) and instrumental artifacts, play a key role in helping us understand the precise chemical composition of Martian samples. The novel approach proposed by Jakubek and team involves modeling the observed Raman bands as a convolution of a Lorentzian IRB and a Gaussian instrument slit function (1).

In their study, the researchers closely examined the calibration target data. By doing so, they were able to determine that SHERLOC possesses a slit function width of 34.1 cm^–1 (1). Knowing this information influenced how they conducted the rest of their experiment. First, they were able to deconvolve the IRB from the observed Raman band, providing a clearer and more accurate representation of the intrinsic bandwidth, free from instrumental artifacts (1). The correlation between the observed Raman bandwidth and intrinsic Raman bandwidth was presented in a concise table, offering a quick estimation tool for spectroscopists working with SHERLOC data (1).

The researchers also delved deeper into their study by applying the calibration to model the SHERLOC spectrum of olivine. Olivine is a mineral rich in magnesium and iron, and it has been identified on Mars through spectroscopic analysis, offering insights into the planet's geological history (1). The presence of olivine suggests past volcanic activity and helps scientists piece together the narrative of Mars' ancient surface composition.

Importantly, the researchers discuss the limitations of the model and provide a quantitative method for calculating associated errors, emphasizing the transparency and rigor applied in their calibration approach. As Mars continues to be a focus of scientific exploration, these advancements in spectroscopic precision promise to deepen our understanding of the Red Planet's geology and potential habitability.

This research not only contributes to the evolving field of planetary spectroscopy but also exemplifies the ingenuity and dedication of the scientific community in unraveling the mysteries of our solar system.

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Reference

(1) Jakubek, R.S.; Bhartia, R.; Uckert, K., et al. Calibration of Raman Bandwidths on the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) Deep Ultraviolet Raman and Fluorescence Instrument Aboard the Perseverance Rover. Appl. Spectrosc. 2023, ASAP. DOI: 10.1177/000370282312108