Ultrafast phase change during femtosecond laser interaction with gold films: Effect of film thickness

Effects of film thickness on ultrafast phase change during femtosecond laser interaction with gold films were studied numerically. The laser pulses were generated in the form of single pulse, multiple pulses, and pulse train. The results show that the melting depth will increase significantly when film thickness is smaller than 600nm, at the expense of a mild rise of the maximum temperature. When the thickness increases above 1100nm, the effect of thickness on the laser-materials interaction is very limited. For multiple pulse irradiations, the dependence of melting depth on pulse number and pulse interval is decided by film thickness. When the film thickness is less than 600nm, more pulses and larger intervals cause deeper melting, while for the thicker film the effects of pulse number and interval are opposite. For pulse train irradiation, the pulse number per train and repetition rate have very limited influence on temperature and melting depth. The pulse interval causes some change in temperature, but not in the melting depth.