Simulation study of positron production from laser-solid interactions

Positron production from ultra-intense laser-solid interactions is investigated using the Monte Carlo code Geant4. The dependence of the positron production on hot electron energy distribution, angular emission and target thickness is examined. The results show that there is at most a 3 times discrepancy in yield comparison if different distribution functions of the hot electrons are used. It is also found that there is no obvious changes in positron yield when different hot electron emission models are used, but the positron beam divergence increases obviously with the hot electron divergence when a Gaussian angular distribution is assumed. In addition, the results indicate that the positron divergence increases with target thickness below 2 mm, above which a saturated trend shows up. The influences of the hot electron divergence, the target thickness and the sheath field on the angular distribution of e+/e- (ratio of positron to electron) and e+/ (ratio of positron to gamma) are studied.