Positron creation using the Titan short pulse laser

Using ultra-intense lasers to generate positrons was theoretically some time ago and demonstrated in principle in two previous experiments where small numbers of positrons were measured. Recently we performed new positron experiments on LLNL Titan laser where we varied laser pulse length, pre-plasma condition, target material and thickness. Using a newly built magnetic spectrometer, we observed copious positrons with good signal-to-background ratio. In addition to positrons, we also simultaneously measured MeV electrons out to 100 MeV and bremsstrahlung photons, in order to confine models for the experiments. This talk will present the detailed experimental results and their comparison with theory and previous experimental data.