Generation and ballistic transport of ultra-short high energy electron bunches in laser-matter interaction at high intensities

Optical transition radiation and proton emission are used to diagnose the fast electrons accelerated during laser-solid target interaction with 300 fs, 1.057 μm, 1019 W/cm2 pulses. The presence of the laser light harmonics in the transition radiation, due to electrons crossing the solid-vacuum interface at the back side of the target, is mainly due to ultra-short electron bunches accelerated by vacuum heating and vxB heating, and separated in time by respectively 1x and fracrm 12 x the laser period. The data show that this emission is consistent with a 2 MeV electron temperature and a ballistic transport from a small spot at the front of the target, comparable to the laser focal spot. The proton emission is used as a complementary diagnostic of all the electrons from the back surface propagating through the target.