Quantum emission of a medium with a time-dependent refractive index

Quantum emission of photons caused by sudden change of the refractive index of a medium is considered. This emission appears due to time dependence of the zeroth quantum state of the field and is a non-stationary analogue of the Casimir effect. A model-exact solution of the problem is presented. If sudden changes of the refractive index are caused by excitation of a semiconductor near to a band-to-band transition by a synchroneously pumped subpicosecond dye laser the intensity of the quantum emission is approximately 10-9 W in the infrared. The analogy of the effect with and its difference from, the Hawking and the Unruh radiations are discussed.