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-critical-density 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 γ -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/mm 2 /mrad 2 /0.1%BW (at 100 MeV) and 1.8 × 10 23 photons/s/mm 2 /mrad 2 /0.1%BW (at 2 GeV) are obtained at a laser intensity of 8.5 × 10 22 W/cm 2 when the plasma density is equal to the critical plasma density n c . 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.