A simple finite element model to study the effect of plasma plume expansion on the nanosecond pulsed laser ablation of aluminum

摘要

In this paper, a simple model was proposed using finite element analysis (FEA) with a commercial FEA software ABAQUS to simulate the two-dimensional (2-D) laser heat transfer in an aluminum material. Without relying on the conventional hydrodynamic model, the proposed model not only predicts the evolutions of the temperature field and ablation profiles in the target material, but also provides an estimation on the evolutions of electron density, plasma temperature, and plasma absorption coefficient. The assumptions used in the model include the local thermal equilibrium and additional assumptions regarding the average plasma temperature and vapor density. The assumptions allowed the laser heat transfer equation to be solved together with the Saha-Eggert equation and conservation equations of matter and charge. When compared to the existing hydrodynamic models, the proposed model solves a less number of nonlinear equations and hence is computationally more efficient. The proposed FE model was employed to study the plasma-shielding effect on PLA produced by a 193 nm Excimer laser and a 266 nm Nd:YAG laser. The predictions of ablation depths, electron density, and plasma temperature agree well with the experimental data. Moreover, effects of the laser intensity and the average plasma temperature on the efficiency of the plasma shielding during PLA were also investigated and discussed in this study.