Generation of pre-bunched electron beams in photocathode RF gun for THz-FEL superradiation

A simple laser technology is proposed to generate a laser pulse sequence with a pulse rate of 2 THz frequency. The laser pulse sequence is used as the driving laser for a photocathode radio frequency (RF) gun. The RF gun generates the pre-bunched electron beams into an undulator for immediate superradiation. Terahertz (THz) radiation, based on a free electron laser (FEL) at a megawatt (MW) level, could be achieved from a compact FEL facility. We describe the laser handling technology for a 16-pulse laser. The detailed calculation of the bunching factor due to the injection phase, beam charge, and bunch number, as well as the differences in the time spacing and energy spread among the laser pulses, are also presented.