Bose-Einstein Condensation of Excitons in the Presence of Laser Radiation

Abstract

The exciton absorption and emission bands in the presence of the Bose-Einstein condensation (BEC) of excitons induced by the coherent laser radiation is considered. The laser radiation creates the coherent macroscopic polarization of the crystal, which is described as a virtual BEC of excitons. The energy spectrum of the elementary excitations as well as the probabilities of the quantum transitions depend essentially on the frequency detuning ${\tilde \Delta }$.

In the neighbourhood of the regions where the new waves arise, the peculiarities of the absorption and emission bands appear. They are related with the properties of the nonequilibrium occupation numbers $n_{\vec q}^{ex}$ arising in the presence of virtual BEC and of coherent polarization of the crystal. In the vecinity of the instability region the ocupation numbers $n_{\vec q}^{ex}$ are finite but anomalous large values. This fact influences on the forms of absorption and emission bands.