Abstract
In the Stark representation, in third-order perturbation theory with respect to fluorescence, it is shown that probability of the ωa + 4Ω harmonic emission in the cooperative fluorescence of two two-level atoms is small and proportional to γ2 / Ω2, Ω2 / ω2 a, contributions to this probability from non-resonant processes being of the order of γ2 / ω2 a.