New insights into the laser produced electron–positron pairs

Abstract

We report new results from the intense laser target interaction experiment that produces relativistic electron–positron pairs. Laser to electron energy transfer, inferred using x-ray and neutron measurements, was found to be consistent with the measured positrons. To increase the number of positrons, one needs to deliver a greater number of relativistic electrons from the laser–plasma interaction to the high Z gold target. A large preplasma was found to have a negative impact for this purpose, while the laser could produce hotter electrons in such preplasma. The peak energy shift in the positron spectrum is confirmed as the post-acceleration in the sheath potential behind the target. The results were supported by a collisional one-dimensional particle-in-cell code. This experiment was performed using the high-power LFEX laser at the Institute of Laser Engineering at Osaka University using a suite of diagnostics measuring electrons, positrons, x-rays and neutrons from the laser–target interaction at the relativistic regime.