QUANTUM RADIATION IN EXTERNAL BACKGROUND FIELDS

A canonical formalism is presented that allows for investigations of q uantum radiation induced by localized, smooth disturbances of classica l background fields by means of a perturbation theory approach. For ma ssless, nonself-interacting quantum fields at zero temperature, we dem onstrate that the low-energy part of the spectrum of created particles exhibits a nonthermal character. Applied to QED in varying dielectric s, the response theory approach facilitates the study of two distinct processes contributing to the production of photons: the squeezing eff ect due to space-time varying properties of the medium and the velocit y effect due to its motion. An alternative quantization method of the electromagnetic field in linear, inhomogeneous but nondispersive dynam ical dielectrics is proposed. The generalization of this approach to f inite temperatures as well as the relation to sonoluminescence is indi cated.