Effect Of Hot Electron Kinetics On Self-Reflectivity Of Warm Dense Gold Irradiated With Femtosecond Laser Pulses

Above the damage threshold of Au nanofoil, experimental and theoretical investigations of the fluence-dependent self-reflection of intense femtosecond laser pulses are presented. Measured reflectance shows not only the fluence-dependency, but also the laser pulse duration dependency, which is barely described by the calculation of dielectric function of high-temperature Au, based on the traditional two-temperature model. A simple hot electron kinetic model, which contains a nonthermalized electronic subsystem cooperated with the two-temperature model, is considered to determine transient electron densities and temperature to calculate the dielectric functions and self-reflection of femtosecond laser pulses. Comparison to experimental data shows the effect of hot electrons with a relaxation time of a few hundreds of femtoseconds on the transient optical properties of gold under a strong excitation.