Cooperative and interference effects in the resonance fluorescence of two identical three-level atoms at high photon densities

Numerical calculations are presented for the excitation spectrum of two identical three-level atoms interacting with a strong resonant laser field. The atoms interact through their dipole-dipole interaction and radiate to each other as well. The spectrum of the symmetric and antisymmetric modes due to the radiative decay from the higher to the lower excited state of the interacting atoms is considered without and with taking into account the effects of the strong pumping process. In the absence of strong pumping, the dipole-dipole interaction in the spectrum of the symmetric modes gives rise to an asymmetric doublet whose ratio of intensities is 2:1, while the spectrum of the antisymmetric modes consists of two peaks one of which represents a stable mode indicating the trapping of a photon between the atoms and a radiative one which has a lifetime one-half that of the isolated atom. In the presence of strong pumping, asymmetries due to the dipole-dipole interaction arise enhancing certain peaks while diminishing the intensity of others and a new pair of sidebands is induced as well. The computed spectra are presented graphically for different values of the Rabi frequencies and the dipole-dipole interaction, respectively.