EXPERIMENTAL-OBSERVATION OF FEMTOSECOND ELECTRON-BEAM MICROBUNCHING BY INVERSE FREE-ELECTRON-LASER ACCELERATION

An electron beam microbunched on the optical wavelength scale of appro ximate to 2.5 mu m by an inverse free electron laser accelerator was o bserved. The optimum bunching was achieved for a 1% energy modulation of a 32 MeV electron beam with 0.5 GW CO2 laser power. The microbunchi ng process was investigated by measuring the coherent transition radia tion produced by the energy modulated electron beam. A quadratic depen dence of the transition radiation signal on the electron beam charge w as observed. The observed shortest wavelength of coherent transition r adiation is less than 2.5 mu m. The debunching process of the microbun ched electron beam was experimentally investigated.