Improvement of the quality and stability of electron bunch using countercrossing laser beam

We demonstrate a highly reproducible acceleration of a high-quality electron bunch injected into the laser wake field accelerator with the help of a countercrossing laser pulse. In our experiments, the wake field is generated by a subrelativistic laser pulse; the second laser pulse collides with the first pulse at 135[degrees], realizing optical injection of electron bunch into the wake field. Because the second pulse is countercrossing, it cannot damage the laser system. The observed electron bunch has the energy of 14 MeV with an 11% (1.5 MeV) spread, the total charge of 22 pC, and a reproducibility of at least 50%. Index Terms--Countercrossing optical injection, laser wake field accelerator (LWFA), monoenergetic electron bunch.