Intense, directional and tunable γ-ray emission via relativistic oscillating plasma mirror.

A mechanism for high energy γ-photon generation based on laser-plasma accelerator is proposed. The laser pulse with a peak intensity of 1022W/cm2 accelerates the electron beam to GeV by the laser wakefield effect. A solid Aluminium target serves as a plasma mirror which is located at the rear side of a gas jet and reflects the laser pulse. High order harmonics are generated due to the Doppler effect experienced by the incident laser. The collisions of the reflected attosecond pulses and the energetic electron beam provide a large cross section for nonlinear Compton scattering and produce a collimated γ-photon flux. The mechanism generates GeV photons with a pulse duration given by the duration of the electron beam.