Resonance fluorescence of localized multiatomic ensembles

The issue of fluorescing multiatomic ensembles is addressed in a somewhat unconventional fashion. We are concerned with the case of an ensemble being localized within a volume small compared to the wavelength. Collective phenomena in resonance fluorescence make its analytical description problematic. We employ the representation due to Holstein and Primakoff of atomic pseudo-spin operators. When the dispersion of the number of excited atoms is small, the kinetic equation turns into that for an effective quantum photonic mode. The new equation is nonlinear. Its stationary solution can easily be found nevertheless. The motion of two fluorescing ensembles is considered as well. Their interaction appears to have geometric nature.