Parametric coupling of frequency components at stimulated Raman scattering in solids

We analyze the effect of parametric coupling of different frequency components at the stimulated Raman scattering threshold depending on the four-wave mixing phase mismatch and material dispersion. A fundamental difference is observed in the way parametric processes affect the generation of Stokes and anti-Stokes waves. We show that as a result of parametric coupling of Stokes components, their generation thresholds strongly decrease and come closer to each other because they originate from an intense parametric rather than a spontaneous seed radiation. The theoretical analysis refines and extends the commonly accepted concept of stimulated Raman scattering in nonlinear crystals and demonstrates good agreement with new experimental data.