A Study of the Energy Spread Effect for an Electron Diffraction Experiment

Abstract

A 2.5 MeV electron beam for femtosecond electron diffraction is generated from a RF photocathode gun with the Brookhaven National Laboratory (BNL) gun IV type at the Pohang Accelerator Laboratory. We use a Ti:Sapphire laser system to illuminate the Cu photocathode with a 100 fs laser pulse. The energy spread of the electron beam is measured to be lower than 0.2% with a 23 degrees RF phase for oblique laser injection. Beam charge is estimated to be its low as 1 pC. The chromatic coherence length is estimated to be 0.106 angstrom. The diffraction patterns for polycrystalline aluminium are studied numerically with several electron beam energies with finite, energy spread. The blurred pattern is quantified to investigate the effect; of the energy spread on the diffraction pattern. A higher energy electron beam blurs the diffraction image more than a lower energy one.