Efficient Raman frequency conversion in liquid nitrogen

The single-pass efficiency of stimulated Raman scattering in liquid N2has been investigated under tight-focusing and collimated-beam conditions keeping the gain-length products approximately constant. In collimated-beam geometry, the gain-length is much greater than important four-wave mixing phasematching coherence lengths, and a 92 percent quantum (80 percent energy) efficiency for generation of the first Stokes Raman output is reported. In the much shorter confocal parameter tight-focusing geometry, parametric processes couple the scattered energy into a number of higher order Stokes components and limit the conversion efficiency into any single component.