Quantum Electrodynamics in Laser Fields

Abstract

The theory to be described here is a special case of quantum electrodynamics (QED) in presence of external (i.e. classical) fields. We shall therefore begin with a short review of this more general topic. The problem of interest is here the influence of given, classical electromagnetic fields on QED. These fields are supposed to be strong, i.e. the coupling of charged particles to the fields is not to be considered as a small perturbation. Some motivation for studying such a theory can be derived from the following reasoning. It is known that a formal solution of QED can be formulated in terms of the free Green’s function in presence of an arbitrary external field. Any approximation to this function implies a corresponding one for QED. The study of special external field problems might give some insight in the machinery, which could help in the general case. To learn what happens if an expansion parameter is no longer small should be easier in special cases than in general (nobody knows really how to sum perturbation theory for a quantum field theory with interaction).

Lecture given at XIV. Internationale Universitätswochen für Kernphysik,Schladming,Austria,February 24–March 7,1975.