Electro-optical measurements of picosecond bunch length of a 45 MeV electron beam

We have measured the temporal duration of 45 MeV picosecond electron beam b unches using a noninvasive electro-optical (EO) technique. The amplitude of the EO modulation was found to increase linearly with electron beam charge and decrease inversely with distance from the electron beam. The rise time of the temporal signal was limited by our detection system to similar to 7 0 ps. The EO signal due to ionization caused by the electrons traversing th e EO crystal was also observed. It has a distinctively long decay time cons tant and signal polarity opposite to that due to the field induced by the e lectron beam. The electro-optical technique may be ideal for the measuremen t of bunch length of femtosecond, relativistic, high energy, charged, parti cle beams. (C) 2001 American Institute of Physics.