Bright attosecond polarized γ-ray emission from the interaction of an intense laser pulse with non-uniform near-critical-density plasma

We study a scheme for the generation of attosecond (as) polarized γ -rays in the interaction of an intense laser with non-uniform near-critical-density (NCD) plasma. Longitudinal and transverse non-uniform plasma channels are used to enhance the efficiency of the γ -ray emission. As the laser pulse propagates in a non-uniform plasma channel, a large number of electrons are first trapped and accelerated to GeV energies and then collide head-on with a laser pulse reflected from a convex plasma mirror; then, γ -rays with energies up to several GeV are emitted. For the longitudinal non-uniform plasma, the γ -ray cutoff energy reaches 2.3 GeV, while it reaches approximately 2 GeV for the transverse non-uniform plasma and only 1.2 GeV for the uniform case. We found that by counting the photons with energy above 1 GeV, a sub-femtosecond γ -ray with a duration of approximately 760 as and divergence angle of 6° is generated in the longitudinal non-uniform plasma. This γ -ray has an unprecedented peak brightness of 5 . 7 × 1 0 26 photons /( s mm 2 mrad 2 0.1%BW) (at 1 GeV). Based on the simulation data, we theoretically calculated the γ photon polarization probability and polarization degree. The results show that the photons are more likely to be emitted into a polarization state that is parallel to the polarization of the background field, and thus possess a positive polarization degree of approximately 0.6. • Attosecond γ -ray generation in a density tailored plasma by an intense laser pulse. • The effect of the plasma density profile on the γ -ray quality. • A theoretical method to γ -ray polarization. • PIC simulation method.