High flux of relativistic electrons produced in femtosecond laser-thin foil target interactions: Characterization with nuclear techniques

We present a protocol to characterize the high energy electron beam emitted in the interaction of an ultraintense laser with matter at intensities higher than 1019 W cm-2. The electron energies and angular distributions are determined as well as the total number of electrons produced above a 10 MeV threshold. This protocol is based on measurements with an electron spectrometer and nuclear activation techniques, combined with Monte Carlo simulations based on the GEANT3 code. The method is detailed and exemplified with data obtained with polypropylene and copper thin solid targets at a laser intensity of 2× 1019 W cm-2. Special care is taken of the different sources of uncertainties. In particular, the reproducibility of the laser shots is considered.