A numerical model for laser ablation with plasma characterization

In this paper a 3-D transient model for laser ablation modelling with plasma plume characterization is presented. The plasma plume was considered in local thermodynamical equilibrium (LTE) and the energy balance permits to evaluate the plume temperature, ion distribution and pressure under the assumption that the gas expansion, from the surface target, produces a sonic front. The plume energy balance is influenced by the energy lost for irradiation from the plume and by the quantity of laser beam energy reflected from the target surface. Then, the physical state of the plasma plume was evaluated by means of the energy balance into the plume which makes it possible to determine the plasma temperature, the plasma ionization and, subsequently, the optical thickness of the plasma. This model predicts the time dependent laser energy delivered to workpiece according to the process parameters and it represents a part of a laser milling simulator previously developed by the authors. A simplified model of the plume geometry is also performed. Numerical simulations have been conducted to quantify this influence on the plasma plume physical state. Several simulation runs are presented in order to show the LAS accuracy and facilities.