Abstract
A THz-pulse-train photoinjector is under construction at the High-energy OPtics and Electronics (HOPE) Laboratory, National Tsinghua University, Taiwan. A beat-wave laser with full tunability in its THz beat frequency is employed to induce the emission of the THz electron pulses from the photoinjector. We show in our study that such a photoinjector is capable of generating periodically bunched MeV electrons with a bunching factor larger than 0.1 at THz frequencies for a total amount of 1 nC charges in a 10-ps time duration. In a linac following the electron gun, velocity bunching compresses the 10-ps pulse width by 20 times and thereby increase the bunching frequency by a factor of 20.