Effect of optical properties on the thermal responses of copper films induced by ultrafast lasers

The optical properties of metal targets subject to ultrafast laser irradiation are dynamically changing. A hybrid method coupling the two-temperature model with molecular dynamics has been used to simulate the femto-and pico-second laser-induced thermal responses of copper films considering the dynamic and constant optical properties. The constant optical properties include an equivalent average reflectivity calculated by setting equally deposited laser energy and an absorption coefficient at room temperature. The results show that the electron and lattice temperatures are little different in both femtosecond and picosecond laser cases, especially for the femtosecond laser with a pulse width far less than electron-lattice relaxation time. As the laser pulse width is comparable to or greater than the relaxation time, e.g., the picosecond laser, the influence of the dynamic change of the optical properties on the melting and re-solidification of the material becomes more significant.