Coherent terahertz radiation from optically pre-bunched electron beams

A bunched electron beam is an efficient source of coherent radiation at wavelengths longer than the bunch length. We describe an experiment demonstrating electron density modulation at 0.8 THz using an optically modulated drive laser to extract a prebunched beam from an RF photoinjector, which is preserved through acceleration to 75 MeV. Measurements of coherent THz transition radiation (CTTR) are presented at the prebunch frequency showing enhanced production over that produced from an unmodulated beam.