Scattering of evaporation particles in ultrashort-pulse laser ablation

Abstract

Ablation phenomena when Gaussian beam of the fourth harmonics of Nd:YAG laser is irradiated to an aluminum substrate in picosecond were simulated using the modified molecule dynamics method that Ohmura and Fukumoto have developed. Scattering velocity of evaporation particles were displayed by vectors, and both molten pool and edge dislocations in the material were visualized. At the same time, the size and velocity distributions of the scattering particles, changes with time of the number of both evaporation atoms and particles, and angle distribution of them were examined quantitatively. Authors have already clarified that there are two types in ablation form. One is explosive ablation and the other is relatively calm ablation. The simulation results showed that the size and velocity of scattering particles and changes with time of the number of particles and atoms, and standard deviation of scattering angle and its transition depend on the ablation form. Even if ablation forms are different, it is common phenomena that ablation particles are divided during scattering process, therefore the number of particles increases gradually, and the scattering angle has a normal distribution.