Femtosecond Electron Diffraction and its Application for Beam Characterization at the PAL

We are proposing a femtosecond electron diffraction (FED) proof of principle experiment at the Pohang Accelerator Laboratory (PAL). The proposed experiment will be performed at the PAL High-Brightness R&D facility using an S-band photocathode RF gun. This paper addresses one of the challenges of FED using photocathode RF gun – smearing of the diffraction patterns due to the beam divergence. Simulation studies for the testing sample -Aluminium are presented. It shows that, diffraction will be detectable if the beam divergence is smaller than 0.3 mrad. Further more, our studies also show that, the 50 μrad beam divergence can be easily observable using the Al diffraction pattern, which could be explored for high-brightness electron beam emittance characterization. The Richardson-Lucy algorithm was used to demonstrate the feasibility of structure reconstruction with FED.