Collisional Relaxation of Super Thermal Electrons Generated by Relativistic Laser Pulses in Thin Solid Targets

The interaction of intense fs laser pulses with matter generates energetic electrons that penetrate deeply into solid targets and deposit energy on sub-ps time scales. Experiments at LLNL's Comet laser facility have used a ps time-resolved K-alpha diagnostic for hot electrons, allowing us to study the highly transient energy transfer between hot and thermal electrons. For hot populations with temperatures of $\sim $500 keV generated by 0.5 ps laser pulses interacting with 12.5 $\mu $m thick Titanium slabs, relaxation times were found to be of the order of 20 ps [1]. Motivated by the discrepancy between the laser- and the K-alpha time scales, we study the roles of various effects that determine the generation of K-alpha radiation: collisional coupling between hot and thermal electrons, plasma expansion, and ionization. [1] H.Chen et al, this conference