The effect of spatial dispersion and boundaries of a medium on resonance radiation transfer

An integral equation is derived for the spectral density of excited atoms using optically dense bounded dispersion media as an example. It is found that the inclusion of the thermal motion of atoms and of the effects due to the existence of a boundary brings about a nonlocal correlation between the concentration of excited particles and the intensity of electromagnetic field in the medium. It is demonstrated that, when the spatial dispersion of permittivity and the boundary effects are disregarded, the obtained result transforms to the well-known Biberman-Holstein equation. The problem on the spectral intensity of radiation of a heated half-space is also investigated.