Lawrence Berkeley National Laboratory

Using higher-order transverse laser modes as drivers for plasma wave excitation, and, in particular, using a ring laser beam with maximum intensity off-axis, results in reversal of the focusing anddefocusing phase regions in a laser wakefield accelerator. This results in improved performance of self-trapping and laser injection schemes. Specifically, the trapping threshold required for opticalinjection is decreased and the maximum energy gain of the trapped electrons is increased. This scheme could also be of interest for the generation of ring electron beams or for beam conditioning.