The 6th International Conference on Matter and Radiation at Extremes (ICMRE2023)

188 / 2023-04-15 16:12:00

Generation of dense and highly polarized positrons by an ultrastrong laser irradiating a solid foil

Fundamental Physics at Extreme Light > Fundamental Physics at Extreme Light-poster

Relativistic spin-polarized positrons play a crucial role in high-energy physics and laboratory astrophysics, yet current techniques face challenges in achieving high polarization and density simultaneously. In this study, we propose a novel scheme for producing ultrarelativistic, dense, and highly polarized positrons. The scheme involves irradiating a solid foil with an ultrastrong laser beam in the strong-field quantum electrodynamics regime.  A directed quasi-static magnetic field $\mathbf{B}^{\rm S}$ is generated by the return current of cold electrons and the fast electron current formed by vacuum heating or $\mathbf{J} \times \mathbf{B}$ heating. This magnetic field $\mathbf{B}^{\rm S}$ dominates the positron production and provides a polarization axis for positrons. Photon polarization effects in polarized positron-electron pair creation are also considered, and this effect is utilized to enhance the polarization degree of positrons. Spin-resolved 3D particle-in-cell simulations demonstrate that dense ($\sim$ 10$^{18}$ cm$^{-3}$) and highly polarized ($\sim$ 70\%) positrons can be obtained utilizing a laser with a peak power of 3.4 $\times$ $10^{23}$ W/cm$^2$. This method shows promise as an alternative polarized positron source for related fields.