Photocathode Design
The aim of this program is to improve the beam quality through development of a cathode that produces a beam with very low thermal emittance. We also aim to increase the quantum efficiency up to the point at which conventional laser technology can be used to produced tailored electron pulses at MHz repetition rate. As a first step, we have investigated metallic photocathodes, and determined that photo-current at the very low photon energies typically used is dominated by surface states. This directly has led to a prediction of the minimum transverse momentum, and to a direction for producing lower emittance though use of other crystalline surfaces. These studies will be extended to metallic systems in which the surface electric field is manipulated using plasmonic interactions, and to semiconductor systems. The latter have the advantage that some degree of thermalization can take place, resulting in colder emission. This work is based on understanding the near Fermi surface electronic structure, through use of very low energy photoelectron spectroscopy, and through electronic structure modeling.
