Resonant Λ medium as a converter of the laser radiation frequency

A theoretical investigation is made of the propagation of two-frequency laser radiation in an optically dense Λ medium in the presence of an rf field which is in resonance with a transition between the lower levels of a Λ-like system of an atom. It is shown that, depending on the phase and amplitude of the rf field and on the initial phases and intensities of the laser waves, one laser wave may be amplified at the expense of the energy of the other wave, or coherent bleaching of the medium (propagation of both waves without intensity losses) may take place.