Nonlinear fluence dependencies in femtosecond laser ablation of metals and dielectric materials

Abstract

We address the peculiarities of femtosecond laser ablation of both metallic and dielectric materials. The ablation process is investigated using two numerical models. For metals, a hydrodynamic model is used that describes the laser light absorption together with heat and pressure wave propagations and the material motion. This model is used to study laser ablation at different fluences for two metals with different strengths of the electron-ion coupling. In these calculations, the role of the temperature-dependent electron heat conduction is demonstrated. For dielectrics, material ionization and laser light absorption processes are modeled in both one and two dimensions. The saturation of the light absorption, and, hence, of the ablation depth, is shown to take place in dielectric materials at sufficiently large laser intensities. The role of this effect on the shape of the craters is examined. This saturation effect is demonstrated to be a consequence of the interplay between the ionization and the light absorption processes.