Scaling of Laser Produced Pair Plasmas And Comparison With Experimental   Data
  We report simulation results of pair production by ultra-intense lasers irradiating a gold target using the GEANT4 Monte-Carlo code. Certain experimental features of the positron and electron energy spectra are reproduced, as well as trends with regard to target thickness and hot electron temperature Te. For Te in the range 5-10 MeV, the optimal target thickness for pair production is found to be about 3 mm. Further Monte-Carlo simulations may aid in the optimization of laser-driven positron sources. 
Alexander Henderson, Edison Liang, Pablo Yepes, Hui Chen, Scott Wilks
physics.plasm-ph astro-ph.HE