The two-photon absorption by a pair of two-level atoms interacting with an incident field is examined. If the laser field is weak, then the existence of the dipole-dipole interaction-induced two-photon resonance follows from the higher-order Fermi golden rule. The effects of spontaneous emission and intense fields on the dipole-dipole interaction-induced two-photon resonance is studied using density-matrix methods. The presence of an intense field is shown to result in a significant enhancement of the two-photon resonance. Numerical results for the probability of simultaneous excitation of two atoms, for the atomic correlations, and for the radiated field intensity are presented.

• Received 5 August 1991

DOI:https://doi.org/10.1103/PhysRevA.45.6721