Quasimonoenergetic electron beam generation by using a pinholelike collimator in a self-modulated laser wakefield acceleration

A relativistic electron bunch with a large charge (>20.3em0exnC) was produced from a self-modulated laser wakefield acceleration configuration. For this experiment, an intense laser beam with a peak power of 20.3em0exTW and a duration of 7000.3em0exfs was focused in a supersonic He gas jet, and relativistic high-energy electrons were observed from the strong laser-plasma interaction. By passing the electron bunch through a small pinholelike collimator, we could generate a quasimonoenergetic high-energy electron beam, in which electrons within a cone angle of 0.250.3em0exmrad $(f∕70)$ were selected. The beam clearly showed a narrow-energy-spread behavior with a central energy of 4.30.3em0exMeV and a charge of 2000.3em0expC. The acceleration gradient was estimated to be about 300.3em0exGeV∕m. Particle-in-cell simulations were performed for comparison study and the result shows that both the experimental and simulation results are in good agreement and the electron trapping is initiated by the slow beat wave of the Raman backward wave and the incident laser pulse.