Enhancing laser ablation inductively coupled plasma mass spectrometry analysis through empirical modeling of crater geometry

Abstract

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) systems are engineered to produce uniform, flat-top beam profiles for optimal surface sampling. In practice, however, rounder beam profiles are prevalent. Their geometrical characteristics can be mathematically described using the two-dimensional super-Gaussian or even a Gaussian function for smaller beam sizes, with the super-Gaussian factor (n) serving as a quantifier. Since the beam profile and the ablation grid have a direct influence on the amount of sampled surface material, the idea is to reduce the ablation grid by sub-pixel mapping to improve the accuracy of surface scanning, increase pixel density, improve spatial resolution, and increase signal-to-noise ratio (SNR). This paper explores the relationship between super-Gaussian order (n), beam size, and laser fluence for circular beams, using two laser ablation systems with different wavelengths – 193 nm and 213 nm nanosecond lasers. An empirical model was developed to yield the factor n, facilitating the determination of the contraction factor (k). Identifying the precise contraction factor for each beam size brings the beam profile closer to a flat-top shape, producing smoother post-ablation surfaces and enhancing image quality due to heightened pixel density. Ultimately, such models improve our understanding of crater geometry optimization, leading to better analytical outcomes in LA-ICP-MS analysis.