EXCITON ABSORPTION AND OPTICAL-GAIN BANDS IN THE PRESENCE OF LASER-RADIATION

The absorption and gain bands of a weak probe signal in the presence o f the Bose-Einstein condensation of excitons, which appears under none quilibrium conditions in a field of coherent laser radiation, are cons idered. It is shown that the absorption of light is caused by a quantu m transition from the ground state of the crystal to the quasiexciton branch of the spectrum. Amplification of the signal occurs as a result of transitions from the quasiexciton branch of the spectrum to the gr ound state of the crystal. (C) 1998 American Institute of Physics.