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.11Nsciescopu

Investigation of Nonequilibrium Electronic Dynamics of Warm Dense Copper with Femtosecond X-Ray Absorption Spectroscopy

Ultrafast optical excitation of matter leads to highly excited states that are far from equilibrium. In this study, femtosecond x-ray absorption spectroscopy was used to visualize the ultrafast dynamics in photoexcited warm dense Cu. The rich dynamical features related to vacancies are observed on femtosecond timescales. Despite the success in explaining x-ray absorption data in the picosecond regime, the new femtosecond data are poorly understood through the traditional two-temperature model based on the fast thermalization concept and the static electronic structure for high-temperature metals. An improved understanding can be achieved by including the recombination dynamics of nonthermal electrons and changes in the screening of the excited block. The population balance between the and bands is mainly determined by the recombination rate of nonthermal electrons, and the underpopulated block is initially strongly downshifted and recovered in several hundreds of femtoseconds.11Nsciescopu