Electro-optic 3D snapshot of a laser wakefield accelerated kilo-ampere electron bunch

Abstract

Laser wakefield acceleration, as an advanced accelerator concept, has attracted great attentions for its ultrahigh acceleration gradient and the capability to produce high brightness electron bunches. The three-dimensional (3D) density serves as an evaluation metric for the particle bunch quality and is intrinsically related to the applications of an accelerator. Despite its significance, this parameter has not been experimentally measured in the investigation of laser wakefield acceleration. We report on an electro-optic 3D snapshot of a laser wakefield electron bunch at a position outside the plasma. The 3D shape of the electron bunch was detected by simultaneously performing optical transition radiation imaging and electro-optic sampling. Detailed 3D structures to a few micrometer levels were reconstructed using a genetic algorithm. The electron bunch possessed a transverse size of less than 30 micrometers. The current profile shows a multi-peak structure. The main peak had a duration of < 10 fs and a peak current > 1 kA. The maximum electron 3D number density was ~ 9 × 1021 m -3. This research demonstrates a feasible way of 3D density monitoring on femtosecond kilo-ampere electron bunches, at any position of a beam transport line for relevant applications.

Snapshot imaging of ultrashort electron bunches

“…Now, writing in Light: Science & Applications , Kai Huang and co-workers from the Kansai Institute for Photon Science, Osaka University, and RIKEN in Japan have succeeded in measuring the three-dimensional (3D) density distribution of a laser-wakefield accelerated electron pulse with femtosecond temporal resolution and micrometer spatial resolution 13 . This single-shot measurement was enabled by combining imaging of optical transition radiation (OTR) - which encodes the transverse profile—with electro-optic (EO) sampling of the OTR—which provides information about the temporal structure (Fig.…”