High-Yield High-Efficiency Positron Generation in High-Z Metal Targets Irradiated by Laser Produced Electrons from Near-Critical Density Plasmas**Supported by the National Basic Research Program of China under Grant No 2013CBA01502, the National Natural Science Foundation of China under Grant Nos 11575011 and 11535001, the National Grand Instrument Project under Grant No 2012YQ030142, and the UK EPSRC under Grant Nos EP/G054950/1, EP/G056803/1,

Abstract

An improved indirect scheme for laser positron generation is proposed. The positron yields in high-Z metal targets irradiated by laser produced electrons from near-critical density plasmas and underdense plasma are investigated numerically. It is found that the positron yield is mainly affected by the number of electrons of energies up to several hundreds of MeV. Using near-critical density targets for electron acceleration, the number of high energy electrons can be increased dramatically. Through start-to-end simulations, it is shown that up to positrons can be generated with state-of-the-art Joule-class femtosecond laser systems.