Ultrabright γ-ray emission from the interaction of an intense laser pulse with a near-critical-density plasma

An efficient scheme for generating ultrabright γ-rays from the interaction of an intense laser pulse with a near-criticaldensity plasma is studied by using the two-dimensional particle-in-cell simulation including quantum electrodynamic effects.We investigate the effects of target shape on γ-ray generation efficiency using three configurations of the solid foils attached behind the near-critical-density plasma:a flat foil without a channel(target 1),a flat foil with a channel(target 2),and a convex foil with a channel(target 3).When an intense laser propagates in a near-critical-density plasma,a large number of electrons are trapped and accelerated to GeV energy,and emit γ-rays via nonlinear betatron oscillation in the first stage.In the second stage,the accelerated electrons collide with the laser pulse reflected from the foil and emit high-energy,high-density γ-rays via nonlinear Compton scattering.The simulation results show that compared with the other two targets,target 3 affords better focusing of the laser field and electrons,which decreases the divergence angle of g-photons.Consequently,denser and brighter γ-rays are emitted when target 3 is used.Specifically,a dense γ-ray pulse with a peak brightness of 4.6×10^(26) photons/s/mm2/mrad2/0.1%BW(at 100 MeV)and 1.8×1023 photons/s/mm2/mrad2/0.1%BW(at 2 GeV)are obtained at a laser intensity of 8.5×10^(22) W/cm2 when the plasma density is equal to the critical plasma density nc.In addition,for target 3,the effects of plasma channel length,foil curvature radius,laser polarization,and laser intensity on the γ-ray emission are discussed,and optimal values based on a series of simulations are proposed.