  The ultrafast laser-induced solid-liquid phase transition in metals is still
not clearly understood and its accurate quantitative description remains a
challenge. Here we systematically investigated, both experimentally and
theoretically, the melting of gold by single femto- and picosecond
near-infrared laser pulses. Two laser systems with wavelengths of 800 and 1030
nm and pulse durations ranging from 124 fs to 7 ps were used and the damage and
ablation thresholds were determined for each irradiation condition. The
theoretical analysis was based on two-temperature modeling. Different
expressions for the electron-lattice coupling rate and contribution of
ballistic electrons were examined. In addition, the number of free electrons
involved in the optical response is suggested to be dependent on the laser
intensity and the influence of the fraction of involved electrons on the damage
threshold was investigated. Only one combination of modelling parameters was
able to describe consistently all the measured damage thresholds. Physical
arguments are presented to explain the modeling results.
