LAUSR

In this paper, we propose to manipulate a nonrelativistic electron beam during its emission and acceleration to create nanobunched electrons. Specifically, we simulate the acceleration of a structured electron beam emitted from a multiring photocathode in a photoinjector and show that, after acceleration, such a transversely structured beam can be transformed into a hollow beam with a longitudinal density modulation in the petahertz frequency range. Our theoretical study shows that, in the far-field zone, the coherent radiation of the bunched hollow beam approaches that of a similarly bunched solid beam in the paraxial limit.