Laser-accelerated electron beams at 1 GeV using optically-induced shock injection

Abstract

In recent years, significant progress has been made in laser wakefield acceleration (LWFA), both regarding the increase in electron energy, charge and stability as well as the reduction of bandwidth of electron bunches. Simultaneous optimization of these parameters is, however, still the subject of an ongoing effort in the community to reach sufficient beam quality for next generation’s compact accelerators. In this report, we show the design of slit-shaped gas nozzles providing centimeter-long supersonic gas jets that can be used as targets for the acceleration of electrons to the GeV regime. In LWFA experiments at the Centre for Advanced Laser Applications, we show that electron bunches are accelerated to 1 GeV using these nozzles. The electron bunches were injected into the laser wakefield via a laser-machined density down-ramp using hydrodynamic optical-field-ionization and subsequent plasma expansion on a ns-timescale. This injection method provides highly controllable quasi-monoenergetic electron beams with high charge around 100 pC , low divergence of 0.5 mrad , and a relatively small energy spread of around 10 % at 1 GeV . In contrast to capillaries and gas cells, the scheme allows full plasma access for injection, probing or guiding in order to further improve the energy and quality of LWFA beams.