Evanescent waves in quantum electrodynamics with unquantized sources

Evanescent waves are studied for a free field satisfying the Helmholtz equation and the results are employed in studying the nature of these waves in the case of a quantized electromagnetic field interacting with a given external source. The identity of these evanescent waves with virtual photons is established, and the result is used to analyze the field due to a uniformly moving charge distribution.