Energy coupling in intense laser solid interactions: material properties of gold

In the double-cone ignition inertial confinement fusion scheme, high density DT fuel is rapidly heated with high-flux fast electrons, which are generated by short and intense laser pulses. Gold cone target is usually used to shorten the distance between the critical surface and the compressed high density DT core. The material properties of solid gold may affect the generation and transport of fast electrons significantly, among which the effects of ionization and collision are the main concerns. In this work, the effects of ionization, collision and blow-off plasma on laser energy absorption rate are investigated using the LAPINS code: A three-stage model is adopted to explain the mechanism of fast electron generation and the change in laser energy absorption rate. With the increase of the charge state of Au ions, the laser-plasma interaction transfers to the later stage, resulting in a decrease in laser energy absorption rate. Collision has both beneficial and harmful effects. On one hand, collision provides a thermal pressure that makes it easier for electrons to escape into the potential well in front of the target and be accelerated in the second stage. On the other hand, collision increases stopping power and suppress electron recirculation within the target in the third stage. The vacuum sheath field behind the target enhances the electron circulation inside the target and thus improves the laser energy absorption, however this effect will be suppressed when the blow-off plasma density behind the target increases or collision is considered.