Generation of good-quality relativistic electron beam from self-modulated laser wakefield acceleration

A relativistic electron bunch with a large charge (similar to 2 nC) was produced from a self-modulated laser wakefield acceleration configuration. In this experiment, an intense laser pulse with a peak power of 2 TW and a duration of 700 fs was focused in a nitrogen gas jet, and multi-MeV electrons were observed from the strong laser-plasma interaction. By passing the electrons through a small pinhole-like collimator of cone f/70, we observed a narrowing in the electron beam's energy spread. The beam clearly showed a small energy-spread behavior with a central energy of 4.8 MeV and a charge of 115 pC. The acceleration gradient was estimated to be about 20 GeV/m.