Measurement of relativistic electron beam bunch length by electro-optic sampling method
Electro-optic sampling measurement of relativistic electron pulses is promising.In this paper the theory and the experiment setup of the measurement are introduced.The coulomb field of electron bunch is analyzed and simulated.The relation of this field with the electro-optic effect of ZnTe crystal is studied.The polarization change of the probe light and the relation of the electron bunch length and the detected signal are calculated by Jones calculus.The results show that the coulomb field of electron bunch should be perpendicular to the axis of ZnTe crystal,the initial polarization of probe light should lie at an angle of 45° or 135° with y″ axis of ZnTe crystal and the fast axis of 1/4 wave plate should lie at an angle of 45° with z″ axis of ZnTe crystal.In such situation,the signal of balance detector will be directly proportinoal to the coulomb field of electron bunch Eb.The purpose of 1/4 wave plate is to move the working point from the nonlinear region to the linear region.The balance detector is used to simplify the relation of the signal of Eb and enhance the SNR.This paper provides a reference for the experiment.