超短パルスレーザによる材料加工現象 ４ ピコ秒パルスレーザアブレーションにおける微粒子の飛散シミュレーション

Abstract

Ablation phenomena when the fourth harmonics of Nd: YAG laser is irradiated to an aluminum substrate during picoseconds were simulated using the modified molecule dynamics method that Ohmura and Fukumoto have developed. Scattering velocity of ablation particles were displayed by vectors, and both molten pool and slip planes in the material were visualized. At the same time, the angle, size and velocity distributions of the scattering particles, both potential and kinetic energies per ablation atom, and ablation energy were examined quantitatively. Authors have already clarified that there are two types in ablation form under constant laser fluence. One is explosive ablation and the other is relatively calm ablation. The former occurs when pulse width is extremely short. The simulation results showed that the angle and size of scattering particles depend on the ablation forms. These differences appear because ablation energy in the explosive process is much larger than that in the relatively calm ablation, that is, kinetic energy per ablation atom becomes very large when the pulse width is extremely short. Velocity of particles also depends on the ablation forms, but the tendency is comparatively weak. Scattering angle in both ablation forms has almost a normal distribution, but the standard deviation in the explosive ablation is much smaller.