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.

Superfluidity of spatially separated electrons and holes and unbalanced twolayer electron system in high magnetic field is considered. The temperature T c of the Kosterlitz-Thouless transition to a superfluid state is obtained as a function of magnetic field H and interlayer separation D. The equation of state for magnetoexciton system in quasi-classical regime is analyzed. The transition from excitonic phase to electron-hole phase is considered. Possible experimental manifestations of the predicted effects are briefly discussed.

No abstract

No abstract