2001 Volume 19 Issue 4 Pages 641-648
An ultrashort-pulse laser is expected as a useful tool for precision microfabrication. The ablation phenomena due to an ultrashort-pulse laser irradiation occur in the period of picosecond order. Therefore, it is very difficult to observe the phenomena insitu. The authors have been conducting the molecular dynamics simulation for many years. In this paper, picosecond-pulse laser ablation phenomena of aluminum were analyzed by the modified molecular dynamics methods, which was developed in last report. Mainly obtained results are summarized as follows: (1) Evaporation does not occur immediately from the beginning of laser irradiation, but starts several picosecond later. (2) There are two types in laser ablation process. One is explosive evaporation which occurs when pulse width is extremely short, and the other is calm evaporation which occurs when pulse width is comparatively long. (3) In the former process, relatively large particles also scatter, and in the latter process, the size of scattering particles is relatively small. Scattering velocity of evaporated particles is several kilometer per second. (4) A shock wave induced by the Gaussian beam irradiation propagates radially from the irradiated center of the prior surface to the interior of the material. It was shown that its propagation velocity is equal to one of elastic wave.
