Eigenfunctions of the Vector-Potential Operator of the Electromagnetic Field and Semiclassical Electrodynamics
Eugeni P. Gordov, Stanislav D. Tvorogov · Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D. Particles and fields · 1973
A complete orthonormal set of eigenfunctions of the vector-potential operator is introduced. It is shown that the semiclassical approximation is naturally determined in the basis of the functions introduced. The extraction of the semiclassical approximation from nonrelativistic quantum electrodynamics allows the determination of the limits of applicability of the semiclassical approach. It is shown that the semiclassical approximation is inapplicable at sufficiently large photon densities. The advantages of using our set of eigenfunctions for the description of the interaction of a strong quantized field with a quantum system are discussed.