Transfer and trapping of resonance radiation in a two-level system

The population kinetics of a two-level system has been theoretically investigated taking into account the transfer of spontaneous radiation under continuous optical pumping. It is shown that, when the photon mean free path in a resonantly absorbing medium is smaller than the characteristic size of this medium or comparable to it, the spontaneous radiation may become an additional pump source. The contribution of spontaneous photons to the kinetics of level has been considered within two approaches. The first approach consists of solution of the radiation transfer equation within the diffusion approximation. The second approach is related to solution of the Biberman–Holstein equation.