Investigation on Heat Transfer Mechanism of Ultrashort Laser Interaction with Metals

The purpose of this paper is to investigate and compare three kinds of two temperature models (TTMs) including the parabolic two-step (PTS) model, the hyperbolic two-step (HTS) model, and the dual-hyperbolic two-step (DHTS) model. First, the thin gold films subject to pico- to femtosecond laser pulses are simulated according to these three TTMs. Comparisons between the electron and lattice temperatures based on different models are presented. The results show that the differences can be neglected for the 20 ps laser, but for the 40 fs laser, the differences between PTS and the other two models are obvious. Then the numerical results are also compared with the experimental data of the damage thresholds for the 28 fs laser. It is found that the PTS model is invalid in simulating this case, and both the HTS model and the DHTS model coincide well with experimental data but the difference between them is still hard to discern. In addition, the interfacial tracking method is applied to the hyperbolic lattice temperature and a detailed comparison between the HTS model and the DHTS model on the beginning time of melting and the maximum ablation depth is presented. It is concluded that when the laser duration is less than 200 fs, the PTS model is invalid. And the beginning time of melting and the maximum ablation depth show remarkable differences between HTS and DHTS.