  We have measured the temporal duration of 45 MeV picosecond electron beam
bunches 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 risetime of the
temporal signal was limited by our detection system to ~70ps. The EO signal due
to ionization caused by the electrons traversing the EO crystal was also
observed. It has a distinctively long decay time constant and signal polarity
opposite to that due to the field induced by the electron beam. The
electro-optical technique may be ideal for the measurement of bunch length of
femtosecond, relativistic, high energy, charged, particle beams.
