Enhancement of Raman scattering by parametric mixing of the pump with its harmonic

A strong focusing of the pump laser is generally used to reduce the Stimulated Raman Scattering (SRS) threshold, but it also produces a phase matching condition in the region of strong gain. This causes a large threshold for SRS in the near infrared due both to the increased diffraction limit and to the destructive interaction of antiStokes-Stokes processes. However the phase matching condition can be used to reduce the threshold by Raman parametric mixing (RPM) of the pump with the second harmonic generated by a fraction of pump. It this way we have observed a lowering of the threshold of about a factor 2.3 and an increase of the SRS of the pump.