Raman response of polar molecules to quasiresonant radiation

A theoretical investigation is reported of the Raman scattering in the rf range by polar molecules. It is shown that an increase in the Stokes frequency ω_s (from zero) results in an increase in the imaginary part of the susceptibility, which governs the spontaneous Raman scattering cross section and the stimulated Raman scattering increment. This increase in the susceptibility is faster than in the optical range by a factor of ω_s². The susceptibility maximum occurs at the Stokes frequency and its width is of the order of the width of the transition line at which the Raman scattering takes place. A further increase in the frequency reduces the resonant contribution to the Raman scattering, and the frequency dependences of the parameters of this contribution approach the dependences typical of the optical range. The influence of the saturation effects on the resonant Raman response is pointed out.