Longitudinal electron bunch profile measurement with electro optic sampling at the radiation source ELBE

At the ELBE Accelerator at the Forschungszentrum Dresden (FZD) we want to perform longitudinal electron bunch profile measurement with Electro Optic Sampling (EOS) technique. We present the preliminary measurement results. The EOS technique is based on the change in the optical characteristics of a birefringent crystal due to the electric field induced by the passage of electrons in the vicinity of the crystal. Therefore we use femtosecond laser (Ti:Sa) pulses to probe the change of birefringence in the electro-optic ZnTe crystal. The resolution in the experiment is limited to about 250 fs by the bandwidth of the detection equipment. One of the important steps in the measurement is to synchronize the Ti:Sa laser pulses emitted with a repetition frequency of 78 MHz with the 13 MHz radio frequency from the superconducting accelerator with low time jitter. The set-up required for determination of the temporal overlap of the femtosecond laser pulse with the real electron bunch was assembled with a OTR sensitive photodiode. The last synchronization step was tuning the time delay of the femtosecond laser relative to the electron bunch by an optical delay unit. By splitting the signal from the ZnTe crystal in a balance detector we achieve information about the longitudinal electron bunch profile.