Heat transfer and phase change during picosecond laser ablation of nickel

This work investigates heat transfer and phase change during picosecond laser ablation of nickel. In this study, ablation of nickel is studied using a mode-locked 25 ps (FWHM) Nd:YAG laser. The threshold fluence for mass removal (ablation) is experimentally determined. Numerical calculations of the transient temperature distribution and kinetics of the solid–liquid and liquid–vapor phase change interfaces are performed. The results show that evaporation is negligible at the free surface, resulting in superheating of liquid to near 0.9Tcr, at which temperature homogeneous nucleation will result in an explosive phase transformation, removing part of the molten layer.