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We discuss the method of parametric excitation of electromagnetic waves in a cavity by creating a dense plasma layer (which represents the "mobile" wall of the cavity) due to irradiation of a semiconductor film with femtosecond laser pulses. The effect is analysed for various initial states including an initial vacuum state. The state of the field produced by this method from an initial vacuum state is different from an electromagnetic field of another origin because only even quantum levels are populated (similar to Schrödinger cat states) and specific distributions of wave packets in phase space takes place. Besides, the parametrically excited field has a specific angle distribution and appears in shorter time scales than the ones required for appearance of radiation of other origin. The instantaneous and adiabatic slow excitation of eigenmodes of the cavity are described. Estimations for experimental detection of the effect are made.

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