Cascaded laser wakefield accelerators (LWFAs) provide a promising route to obtain controllable multi-GeV QM e beams. Furthermore, the ability to stage together multi-LWFAs is of vital importance for eventually implementing practical 10-GeV and higher-energy laser accelerators, whereby the electrons are repeatedly accelerated by the laser wakefields in a manner similar to the conventional accelerators.

Researchers at State Key Laboratory of High Field Laser Physics——Shanghai Institute of Optics and Fines Mechanics (SIOM/China) report on the first near-GeV QM e beams generation from an all-optical cascaded LWFA. Electron injection and acceleration are successfully separated and controlled in different LWFA stages by employing two gas cells filled with a He/O2mixture and pure He gas, respectively. [ PHYSICAL REVIEW LETTERS 107, 035001 (2011)] 

They have demonstrated the generation of near-GeV QM ebeams from an all-optical cascaded LWFA by using tunnel-ionization injection in the first LWFA and optimizing the electron seeding and self-guiding of the laser pulse in the second LWFA. A QM ebeam with peak energy of 0.8 GeV was obtained by the second LWFA from the seeded e beam with a continuum spectrum below 50 MeV, which was generated in the first LWFA.The cascaded LWFA scheme developed here can be scaled up to the generation of multi-GeV ebeams in a straightforward way by using a long preformed plasma channel as the second LWFA.

FIG.(color online). Measured transmitted laser spectra at the exit of LWFAs