Nanosecond laser ablation modeling of silicon and tungsten as support activity for LIBS diagnostic

Laser-Induced Breakdown Spectroscopy (LIBS) analyzes the optical emission of a laser-induced plasma to determine the elemental or isotopic composition of a material. In nuclear fusion research, LIBS is a promising diagnostic for remote monitoring of Plasma-Facing Components (PFCs). Accurate interpretation of LIBS measurements, especially for depth profiling and fuel retention studies, requires the knowledge of ablation rate and laser-induced thermal effects. This work presents a two-dimensional thermal model, developed with COMSOL Multiphysic, to simulate nanosecond laser ablation of tungsten, a fusion-relevant metal, and silicon, selected for its different thermophysical properties. The model solves of the heat conduction equation considering temperature-dependent material properties, phase change, latent heat consumption, and plasma plume shielding included via an exponential attenuation factor. Material removal is implemented through a mesh deformation velocity dependent on the assumed ablation regime. Model validation was performed by comparing computations with laser ablation experiments in vacuum, using a 10 ns Nd:YAG laser. Ablation craters were characterized by optical microscopy, mechanical profilometry, and Scanning Electron Microscopy (SEM). For tungsten, normal evaporation was considered to describe ablation for 0.4 − 2mJ pulse energy (∼ 4 − 20 J/cm2 considering central crater); for silicon phase explosion dominated at 4 − 20mJ (∼ 25 − 60 J/cm2). The model reproduced ablated volume, depth, and crater diameter, obtaining relative discrepancies on depth resolution prediction around 20%. These results demonstrate the potential of a physics-based model to predict LIBS crater features, supporting parameter optimization