Impact of Beam Profile on Raman Spectroscopy Measurements

ABSTRACT Characterisation and optimisation of the laser beam profile in Raman spectroscopy is critical to ensure accuracy and reproducibility of measurements, especially for heterogeneous or sensitive samples. The laser beam profile has a significant effect on the axial resolution and energy distribution on the sample, thus influencing the focal spot size and excitation volume. An optimal profile minimises the focal volume, improving signal‐to‐noise ratio (SNR) and confidence in spectral contributions. Understanding and addressing distortions in the beam profile can aid optimisation of the optical alignment or mitigate spectral artefacts, increasing SNR and confidence in data quality. In this study, three Raman instruments with eight different light paths were analysed to evaluate their beam profiles. The results showed that most instruments exhibited beam profile aberrations generated during propagation from the laser source to the objective. Theoretical models were used to assess how ideal and distorted beam profiles affect the resulting focal volume. A simple practical guide for measuring the X–Y spatial characteristics of the beam profile in a confocal Raman microscope was also developed to aid researchers in measuring the quality of their beam delivery. This work highlights the importance of identifying beam distortions and aids awareness of the implications on the optical characteristics of the focal spot; ultimately, how this may impact the quality of Raman spectroscopy data.