Resonance effects in the interaction between a two-level system and intense polychromatic radiation

A theoretical investigation is made of the interaction between a two-level system and an electromagnetic field with an equidistant spectrum having arbitrary independent spectral-component phases (multimode laser radiation). The concept of the generalized Rabi frequencies of a two-level system situated in a polychromatic field is introduced, and the values of these frequencies are calculated. It is shown, that extrema (resonances) whose positions are independent of mode phases exist in the dependence of the population-difference harmonics and the absorption coefficients of individual modes on the intermode interval and the field intensity. The resonances correspond to the coincidence of mode-beat combination frequencies with the generalized Rabi frequencies.