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

An electron beam microbunched on the optical wavelength scale of {approx}2.5 {mu} m by an inverse free electron laser accelerator was observed. The optimum bunching was achieved for a 1{percent} energy modulation of a 32MeV electron beam with 0.5GW CO{sub 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 {mu}m . The debunching process of the microbunched electron beam was experimentally investigated. {copyright} {ital 1998} {ital The American Physical Society}