Time-dependent models of field-assisted photoemission

Summary form only given. We describe a time-dependent photoemission model and apply it to modeling emission from structures where field variation occurs as a consequence of geometrical or local variations. A prolate spheroidal model may be used to obtain the field distribution along the surface of the emitter as well as the incident angle for laser light illuminating the apex. We present the results of an analysis modeling the quantum efficiency of a sharp metallic emitter illuminated by lasers of various wavelengths as a function of applied field, laser intensity, and parameters specific to the emitter. Such information is required to address energy distributions and emittance growth of the beam from a needle cathode or microfabricated structures, but the techniques may also be applied to, e.g., a dispenser cathode whose work function has been lowered by coatings.