Chapter Four - Generation of Ultrashort Electron Bunches for Time-Resolved Electron Diffraction Experiments

Abstract

Chapter 4 considers the results of the design of 500 fs photoelectron gun with electrostatic focusing to be used in time-resolved electron diffraction experiments. The photoelectron gun represents a source of photo-induced, well-collimated (divergence <0.5°), sharp (effective diameter < 0.7mm), ultrashort (duration about 500 fs) bunches of electrons. Demonstration experiments in transmission mode with an aluminum sample of 300 A thicknesses resulted in diffraction pattern of reasonable quality under accumulation of up to 4 × 104 electron bunches with about 1500 electrons per each single bunch. Theoretical and experimental aspects of temporal focusing of electron bunches in time-dependent electric fields are also considered. Main essence of this approach is based on the fact that a real temporal focusing of photoelectron bunch can be attained using a properly chosen electric ramp. This new technology allows a real breakthrough in time resolution of photoelectron guns and diffractometers designated for time-resolved electron diffraction experiments.