New insights into the laser produced electron-positron pairs

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.