Quantum radiation in external background fields

A canonical formalism is presented that allows for investigations of quantum radiation induced by localized, smooth disturbances of classical background fields by means of a perturbation theory approach. For massless, nonself-interacting quantum fields at zero temperature, we demonstrate that the low-energy part of the spectrum of created particles exhibits a nonthermal character. Applied to QED in varying dielectrics, the response theory approach facilitates the study of two distinct processes contributing to the production of photons: the squeezing effect due to space-time varying properties of the medium and the velocity effect due to its motion. An alternative quantization method of the electromagnetic field in linear, inhomogeneous but nondispersive dynamical dielectrics is proposed. The generalization of this approach to finite temperatures as well as the relation to sonoluminescence is indicated.