Electron Beams as Carriers of Optical Coherence

Abstract

Recently there was reported an unusual experiment in which an electron beam appears to be able to transport laser light from one place to another.[1] In this experiment an electron beam first interacts with a laser field in the presence of a thin dielectric film and then subsequently emits light at the laser frequency when it impinges on a second (non-flourescent) dielectric film. While this result is still unconfirmed, it has stimulated much theoretical interest in the possibility of using electrons as carriers of optical coherence. The fact that electron beams can carry coherence in the microwave region has been known since the advent of the kylstron. In this frequency region the coherence time of the electrons is short compared to the period of oscillation of the electromagnetic waves, and the classical theory which treats the electrons as point charges is completely satisfactory. In the optical region, however, the electron coherence time can be long compared to the period of the oscillation and the electron wave packets are modified by the presence of the field. Thus the classical point charge approximation is no longer valid.