Fast electron transport and induced heating in aluminium foils

Beams of fast electrons have been generated from the ultra-intense laser interaction with Aluminium foil targets. The dynamics of the fast electrons propagation and the level of induced in-depth heating have been investigated using the optical emission from the foils rear side. Important yields of thermal emission, consequence of high target temperatures, were detected for targets thinner than 50 μm. We precisely characterized the targets in-depth temperature profile in order to reproduce the emission yields. At shallow depth, we show the important heating (estimated to > 100 eV till 15 μm depth) has a resistive origin upon the neutralizing return current. For deeper regions, because of the bulk component divergence, the fast electron energy losses and induced heating are due to collisions. Coupling the model to the experimental measurements, we were able to quantify the bulk of the fast electron population, corresponding to 35% of the laser energy and a 500 keV temperature