156 / 2023-04-14 22:24:13

Dense polarized positrons generated by laser-plasma interactions

laser-plasma interaction,PIC simulation,strong-field QED,spin and polarization effects

极端光下的基础物理学 > QED效应和核物理-海报

Thanks to the rapid development of chirped pulse amplification (CPA) and other related technologies, several 10-PW-class and 100-PW-class lasers are being built or planned worldwide [1]. These high-power lasers can reach peak power densities of 10²¹⁻²⁴ W/cm² when tightly focused on the micron scale. In such a strong laser field, quantum electrodynamics (QED) will dominate [2]. Over the past decades, a lot of research has been carried out on strong-field QED physics, and several proposals have been put forward for generating high-quality sources of gamma photons or positrons. However, electron-positron spin and photon polarization effects have often been neglected. These spin and polarization effects on the photon emission and pair production in ultra-intense laser-plasma interactions are still unknown.



To self-consistently study strong-field QED processes in laser-plasma interactions, we have developed the polarized QED-PIC code, named YUNIC [3], which includes electron-positron spin and photon polarization effects. Using this code, we have also investigated the interaction of a 100-PW-class laser with the solid target. The simulation setup is common in real experiments, where a linearly polarized laser pulse and a solid target with micron-scale long preplasmas are adopted [4]. The simulation results show that the positron polarization becomes apparent when the laser intensity exceeds 10²⁴ W/cm². The polarization degree is dependent on the transverse deflection angle of positrons. For positrons with deflection angles greater than 20 degrees, the polarization can reach 30% with a density of 10¹² per steradian and a charge of 30 nanocoulomb. This implies that for future 100-PW ultra-intense laser interactions with solid targets, polarized positrons will be ubiquitous. The generated dense polarized positrons could be used in future electron-positron colliders and laboratory astrophysics.