Knife-Edge Technique Using Raman Spectrometers to Determine the Effective Laser Spot Size on Powders: Implications...

Area of Science:

• Planetary Science
• Analytical Chemistry
• Geoscience

Background:

• Raman spectroscopy is vital for Earth and planetary sciences, with miniaturized instruments deployed on Mars missions (e.g., SuperCam, SHERLOC, RLS).
• Analysis of Mars analogue samples requires consistent spectrometer characterization, but laser spot size is often unreported.
• Inconsistent reporting of laser spot size hinders comparability of Raman spectrometer capabilities across studies.

Purpose of the Study:

• To develop an easy, fast, and universal experimental approach for determining the effective laser spot size in Raman spectroscopy.
• To characterize the effective laser spot size of different Raman spectrometers (benchtop and portable) using standard samples.

Main Methods:

• Developed and applied a universal experimental method to measure effective laser spot size.
• Characterized laser spot size using a silicon wafer and gypsum powders with varying grain sizes.
• Tested a benchtop micro-Raman system and two portable spectrometers.

Main Results:

• Successfully determined the effective laser spot size for diverse Raman spectrometer systems.
• Investigated the influence of sample grain size on the measured laser spot size.
• Provided a method to ensure comparability of Raman data for remote planetary missions.

Conclusions:

• The developed method offers a standardized approach to measure effective laser spot size, crucial for mission-relevant sample analysis.
• Understanding laser spot size dependence on sample grain size is important for accurate qualitative and quantitative analysis of solid dispersions.
• This work enhances the reliability and intercomparability of Raman spectroscopic data from planetary exploration.