Modeling of ultrafast phase changes in metal films induced by an ultrashort laser pulse using a semi-classical two-temperature model

A semi-classical two-temperature (2T) model, together with the extended Drude model for temperature-dependent optical properties, is proposed to describe ultrafast thermal transport and phase changes in gold films irradiated by an ultrashort laser pulse. This model reduces to a classical 2T model when the electron momentum equation and the two terms related to electron drifting velocity in the electron energy equation are dropped off. It is found that the significant changes in reflectivity and absorption coefficient due to rapid temperature rise could drastically alter laser energy deposition and in turn, the thermal response in metal films. It is also found that the semi-classical 2T model could predict lower electron and lattice temperature and less severe solid-liquid and liquid-vapor phase change than the classical 2T model. The difference could be more distinct with increase of laser fluence and/or increase of laser pulse duration.