Deciphering in situ electron dynamics of ultrarelativistic plasma via polarization pattern of emitted γ -photons

Understanding and interpretation of the dynamics of ultrarelativistic plasma is a challenge, which calls for the development of methods for in situ probing the plasma dynamical characteristics.We put forward a new method, harnessing polarization properties of γ -photons emitted from a non-prepolarized plasma irradiated by a circularly polarized pulse.We show that the angular pattern of γ -photon linear polarization is explicitly correlated with the dynamics of the radiating electrons, which provides information on the laser-plasma interaction regime.Furthermore, with the γ -photon circular polarization originating from the electron radiative spin flips, the plasma susceptibility to quantum electrodynamical processes is gauged.Our study demonstrates that the polarization signal of emitted γ -photons can be a versatile information source, which would be beneficial for the research fields of laser-driven plasma, accelerator science, and laboratory astrophysics.