Radiation Electrodynamics of the Photo-Electron Cloud Produced By an ArbitraryPhoton Pulse Incident on a Planar Emitting Surface in Vacuum

摘要

The electromagnetic radiation field produced by the cloud of acceleratingelectrons induced at a planar photoelectron emitting surface in vacuum by a photon pulse of arbitrary time profile incident upon that surface is derived analytically in the nonrelativistic, small-spot-size regime. This derivation provides scaling relations for the radiated fields explicit in the pulse and surface parameters. Electron cloud dynamics are discussed and integral expressions for the electric and magnetic fields at large but finite (i.e., 'finitely-remote') distances from the cloud are derived. The fields are calculated by directly summing contributions over individual electron trajectories, using exact small-spot retarded times, rather than by the usual technique of first forming the electron charge and current densities and integrating them. The resulting integral representation of the finitely-remote fields are correct to first order in v/c and are valid for all time and for somewhat spatially extended charge clouds. These finitely-remote fields are then used to compute asymptotic radiation fields in the limit of the field point going to infinity in a suitable fashion. From these asymptotic radiation quantites in which all the integrations have been fully carried out are then derived. Illustrations of the general results for some sample pulses (constant, linear ramp, triangular, parabolic, and sq sin) are provided.