The effect of stokes-antistokes coupling on the gain of resonant stimulated raman scattering

In non-resonant stimulated Raman scattering under phase-matched conditions the Stokes-antiStokes coupling results in suppression of the exponential gain of both the Stokes and the antiStokes fields to zero. This phenomenon, known as parametric gain suppression, leaves the intensity of the laser beam passing through the medium practically unchanged, as the Stokes and the antiStokes processes cancel each other. We consider the effect of Stokes- antiStokes coupling on the gain of these two fields in the case of resonant stimulated Raman scattering (rsrs), when the pump laser is resonant with one of the intermediate states. The analysis shows that as one approaches the conditions for rsrs, the gain suppression due to the Stokes-antiStokes coupling under phase-matched conditions becomes smaller and smaller, and the gain of the Stokes intensity approaches the value for zero Stokes-antiStokes coupling. Furthermore, one finds that sufficiently close to resonance the antiStokes gain is largest under complete phase-matched conditions (although considerably smaller than the gain for the Stokes field under the same conditions), and it decreases to zero with increasing mismatch with a Lorentzian dependence of the gain on the mismatch parameter Ak. The cancellation of the parametric gain suppression for rsrs is a result of the fact that near resonance the non-linear susceptibility at the Stokes frequency becomes much larger than that at the antiStokes frequency.