Instantaneous approximation for the dynamical Casimir effect

The one-dimensional model for the dynamical Casimir effect, i.e. the effect of creation of photons in a nonstationary cavity, is studied in the framework of the instantaneous approximation. Different exact and approximate expressions for the energy distribution of created photons are derived. A region of applicability of the instantaneous approximation is established. In particular, it is shown that the instantaneous approximation predicts no more than the low-energy part of the energy distribution. Recent proposals for experimental realization of a cavity with fast variation of parameters are reviewed, and a new proposal based on fast creation of an additional mirror in the interior of the cavity by instant injection of dense electron plasma in thin semiconductor film is presented