Generalized model of laser-induced peak asymmetry in Raman lines

The rate and precision at which samples can be scanned by Raman spectroscopy strongly depend on laser and material parameters. In this article, we describe the trade-off between parameters that increased laser intensities to improve resolution and reduce integration times, and its effect on thermally induced shift and asymmetric broadening of the line profile, especially in the case of resonant Raman. We present an analytical approximation to describe this phenomenon for all volumetrically absorbing materials and a wide range of laser parameters. This allows the determination of an optimal scan rate for the sample material and the required optical resolution, or vice versa, the determination and accurate correction for thermally induced shifts and asymmetries. This study provides an analytical quantification of this often-neglected line asymmetry and allows us to correct for its impact on the signal with few material properties and laser parameters. It may, in particular, allow us to discriminate this effect against other sources of peak asymmetry due to intrinsic properties. We obtain this analytical expression by condensing a parametrized finite element method model into a heuristic probability density function of temperature that describes the full parameter space. This function can be applied to any thermally undistorted line shape by convolution to determine a corrected line profile. This profile then provides a parameter-dependent optimized fitting function for an optimal determination of Raman signal parameters. Published under an exclusive license by AIP Publishing.

Automated summary

The article discusses the relationship between laser and material parameters and the rate and precision of Raman spectroscopy scanning. It also examines the effects of thermally induced shift and asymmetric broadening on the line profile. An analytical approximation is presented to describe this phenomenon and correct for its impact on the signal. The study provides a quantitative analysis of line asymmetry and allows for optimal determination of Raman signal parameters.