Transition of dominant heating process from relativistic electron beam heating to thermal diffusion in an over picoseconds relativistic laser-solid interaction

Abstract

A mechanism of isochoric heating of a solid density plasma by a kilojoule (kJ) class laser with relativistic intensity and a ten picosecond (ps) pulse duration is delineated by collisional Particle-in-Cell (PIC) simulations. Before an emergence of kJ class lasers, plasma heating by the laser-accelerated relativistic electron beam (REB) has been studied as the dominant isochoric heating process by intense lasers. A recent experiment using a kJ class laser indicates that the thermal diffusion from the hot plasma surface becomes the dominant process of the isochoric heating in the ps scale laser irradiation. In this article, we demonstrate that a transition of the dominant isochoric heating process from the REB heating to the thermal diffusion happens in the 10 ps laser irradiation. The diffusion heat front propagates with the speed approximately 2 μm/ps in an Aluminum target. Additionally, the hot dense plasma expands to create a steep laser-plasma interface, which is found to reduce REB energy.