We present the classical and quantum theory of time refraction in a generic nonstationary medium. The classical approach leads to expressions for the temporal refraction coefficient, and the temporal Fresnel laws are given. The quantum formulation leads to the derivation of instantaneous Bogoliubov transformations and the evaluation of the number of photon pairs created from vacuum by the temporal changes in the medium. The influence of boundary conditions, the connection of this model with the dynamical Casimir effect, and radiation from superluminal nonaccelerated optical boundaries is also discussed.

• Received 19 July 2005

DOI:https://doi.org/10.1103/PhysRevA.72.063805