Fast Electron Transport in Ultraintense Laser Pulse Interaction with Solid Targets by Rear-Side Self-Radiation Diagnostics

We report on rear-side optical self-emission results from ultraintense laser pulse interactions with solid targets. A prompt emission associated with a narrow electron jet has been observed up to aluminum target thicknesses of $400\ensuremath{\mu}\mathrm{m}$ with a typical spreading half-angle of $17\ifmmode^\circ\else\textdegree\fi{}$. The quantitative results on the emitted energy are consistent with models where the optical emission is due to transition radiation of electrons reaching the back surface of the target or due to a synchrotron-type radiation of electrons pulled back to the target. These models associated with transport simulation results give an indication of a temperature of a few hundred keV for the fast-electron population.