Experimental Observation of Femtosecond Electron Beam Microbunching by Inverse Free-Electron-Laser Acceleration

Abstract

An electron beam microbunched on the optical wavelength scale of $\ensuremath{\approx}2.5\ensuremath{\mu}\mathrm{m}$ by an inverse free electron laser accelerator was observed. The optimum bunching was achieved for a 1% energy modulation of a 32 MeV electron beam with 0.5 GW ${\mathrm{CO}}_{2}$ laser power. The microbunching process was investigated by measuring the coherent transition radiation produced by the energy modulated electron beam. A quadratic dependence of the transition radiation signal on the electron beam charge was observed. The observed shortest wavelength of coherent transition radiation is less than $2.5\ensuremath{\mu}\mathrm{m}$. The debunching process of the microbunched electron beam was experimentally investigated.