BROAD-BAND FREE-ELECTRON LASER BY THE USE OF PREBUNCHED ELECTRON-BEAM

Using prebunched electrons of 35 MeV from a linear accelerator, we hav e constructed a new type of free electron laser (FEL) which has a quas icontinuous spectrum in the millimeter wave region. The FEL consists o f an open resonator and a bending magnet. Wave packets of coherent rad iation from electron hunches are stored in the resonator to stimulate the radiation from the following bunches. The accumulated radiation is composed of overtones of the radio frequency of the accelerator and i s quasicontinuously distributed over a wide region; By tuning the reso nator, either all overtones or a part of them are amplified.