Combined plasma lens and rephasing stage for a laser wakefield accelerator

Abstract Electrons from a laser wakefield accelerator have a limited energy gain due to dephasing, and are prone to emittance growth causing a large transverse divergence. In this paper, we experimentally show that both of these issues can be addressed in a single step, by adjusting the plasma density profile. Shock-assisted ionisation injection is used to produce 100 MeV quasi-monoenergetic electron bunches in the primary part of the accelerator. Downstream from accelerator, a second, independently tuneable density region is added which can be used to both boost the energy of the electron bunches, and as a plasma lens for significant divergence reduction. An additional energy gain of 25% and a 40% divergence reduction is obtained. The effects are validated by theoretical models.