New results on the laser produced positrons using the TITAN and OMEGA EP lasers*

We performed new experiments and simulations on generating positrons with intense lasers [1]. A cone shaped positron jet is produced by irradiating a gold target with an intense picosecond duration laser pulse. The jet has $\sim $20 degree angular divergence and a quasi-monochromatic energy distribution with energy 4 to 20 MeV. The conversion efficiency from laser energy to positrons in the jet is $\sim $ 2x10$^{-4}$. The positron angular and energy distributions are controlled by the laser and target conditions. The positron acceleration mechanism is identified experimentally as the sheath electric field on the rear surface of target. This talk will present the details of these new experimental and simulation results.\\[4pt] [1] Hui Chen, S. C. Wilks, D. D. Meyerhofer et al., PRL 105,015003 (2010)