In this work, Molecular Dynamics (MD) simulation is employed to investigate femtosecond laser ablation of copper, with an emphasis on the understanding of the mechanism of phase change during laser ablation. Laser induced heat transfer, melting, surface evaporation, and material ablation are studied. Theoretically, it has been suggested that under intense femtosecond laser irradiation, the material undergoes a volumetric phase change process; its maximum temperature can be close to or even above the thermodynamic critical point. The MD simulations allow us to determine the transient temperature history of the irradiated material and to reveal the exact phase change process, which explains the mechanisms of femtosecond laser ablation. A finite difference calculation is also performed, which is used to compare results of heating and melting prior to a significant amount of material being ablated.
