A study of electro-optical crystal as a diagnostic tool for low energy electron beam

Abstract

The short, intense, and low emittance electron beams are crucial to make high quality X-ray beam for X-ray free electron laser (XFEL). A RF photo-cathode (RF PC) gun of 1.6 cell cavity is installed at Gun Test Stand (GTS) in Pohang Accelerator Laboratory (PAL). For the successful construction of PAL-XFEL, the bunch length of the beam should be measured accurately at the exit of the gun where the beam energy is 4.5 MeV. Electro-Optic Sampling (EOS) is a very promising method to measure the bunch length non-destructively. An experiment with D.C. voltage setup is done to verify the electro-optic (EO) crystal can be used as a diagnostic tool for low energy beam. A simulation study is also done with a pulse propagation method which is based on the Fourier transform that allows us to investigate the dynamical evolution of electromagnetic pulse in the EO crystal. The simulation result shows that the signal level can be about 20 % of the initial laser pulse signal. From the experiment and the simulation, we have convinced that the EOS can be a non-destructive diagnostic tool for low energy beam for XFEL.