A scheme to produce mega-electron-volt- (MeV) level gamma rays with a high level of brilliance, a small divergence angle, and controllable angular momentum from Laguerre-Gaussian (LG) laser-pulse interactions with underdense plasma is proposed. Three-dimensional particle-in-cell simulations show that the gamma photon beam acquires angular momentum from the helically distributed relativistic electrons driven by the LG laser and the self-generated fields in the plasma bubble created by the laser. The divergence angle and the orbital angular momentum (OAM) of the gamma photons can be controlled by manipulating the laser parameters. It is found that a 1-MeV helical gamma-ray pulse with peak brightness 2.23×1024photons/s/mm2/mrad2/0.1%BW and angular momentum 7.1×10-15kgm2/s, as well as a

Astrophysical phenomena; Circularly polarized; Laser pulse interaction; Orbital angular momentum; Quantum electrodynamics; Relativistic electron; Three dimensional particle-in-cell simulations; Underdense plasmas

Institute of Applied Physics and Computational Mathematics