Thermoelastic Vibration of Nickel Film Irradiated by Femtosecond Laser: Molecular Dynamics Study

A detailed understanding of the physical essence of the interaction between a femtosecond laser and its target material remains an important and challenging goal. In this paper, the thermoelastic vibration behavior of nickel films irradiated by a femtosecond laser is studied by a molecular dynamics method combined with a two-temperature model. The model fully defines the spatial distribution of laser energy, the photoelectron coupling, and the electron-lattice coupling, and elucidates the temperature and stress evolution within the nickel film under femtosecond laser irradiation. Furthermore, the whole process and the mechanism of thermoelastic vibration is revealed at the atomic level. The thermoelastic vibration is divided into two stages, including continuous expansion during the process of energy relaxation and periodic expansion and contraction after reaching thermal equilibrium. The elastic oscillation of thin films is driven by periodic changes in energy, including the energy of atomic thermal motion and collective atomic motion. The effect of pulse fluence on thermoelastic vibration is also discussed in detail to provide reasonable suggestions for limiting this effect. This study provides the theoretical foundation and a feasible method for a deeper understanding of the interaction mechanisms between femtosecond lasers and materials.