Numerical simulation and experimental study of femtosecond laser ablation of copper: A two-temperature model with temperature-dependent properties and multiple phase transitions

A fundamental study of the interaction between femtosecond laser and copper will be useful in optimizing laser parameters and processing quality in practice, and it faces challenges due to very short action time, complex energy transport and phase transition processes of this interaction. In this paper, A 2D two-temperature model was established and improved to include temperature-dependent optical and thermophysical properties and three phase transitions including melting, vaporization, and phase explosion. The temperature evolution of both the top surface and the sub-surface were simulated, thereafter, ablation experiments with different laser peak fluences were conducted using a femtosecond laser. It was found that the interface reflectivity would decrease rapidly, while the optical penetration depth and the ballistic electron penetration depth would increase significantly during laser irradiation. The temperature evolution of electron and lattice subsystems of the top surface could be divided into, respectively, 4 and 5 stages with different temperature trends in each stage. The variation of subsurface temperature was different from that of surface temperature and the temperature distribution showed that there was a temperature peak at near surface. A comparison of the experimental and simulation results showed that the simulated ablation depths were consistent with the experiment results.