A relativistic electron bunch with a large charge $(>2\mathrm{nC})$ was produced from a self-modulated laser wakefield acceleration configuration. For this experiment, an intense laser beam with a peak power of $2\mathrm{TW}$ and a duration of $700\mathrm{fs}$ 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 $0.25\mathrm{mrad}$ $(f∕70)$ were selected. The beam clearly showed a narrow-energy-spread behavior with a central energy of $4.3\mathrm{MeV}$ and a charge of $200\mathrm{pC}$. The acceleration gradient was estimated to be about $30\mathrm{GeV}∕\mathrm{m}$. 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.

• Received 14 September 2005

DOI:https://doi.org/10.1103/PhysRevE.73.016405