Hot electron generation at a steep interface in super intense laser-matter interaction

Super intense laser light (> 1020 W/cm2) is able to sweep preplasma over short times and compress the preplasma density gradient typically generated by the prepulse of today's high-intensity, high energy laser systems. Hot electron generation at steep plasma density gradients has been studied in a previous paper [Kemp et al., Phys. Rev. Lett. (2008)], which identified a mode of hot electron acceleration that is characterized by the formation of low-density shelf in front of the target. In this paper, we study the direct interaction mode, which appears after the shelf plasma interaction. We propose an analytical model to describe the absorption, explain electron energy spectra, and identify the parameter regime where the direct interaction mode becomes important.