Nonlinear competing processes in multifrequency Raman generation

We investigate the extent to which the Raman generation of ultrabroad-band light will be affected by nonlinear competing processes. The model equations are generalized to incorporate an off-axis competing signal and a quantitative study is undertaken of its affect on the primary process. An effective gain-length product for the parasitic process is introduced and its characteristics examined. A simple analytical model has been developed for the case of a competing process generated from background noise or amplified spontaneous emission. Predictions of this model are found to be in good agreement with numerical simulations. We find that the efficiency and character of ultrabroad-band multifrequency Raman generation, with resonant and symmetric pumping, effectively drives such nonlinear competing processes below threshold. The roles played by dispersion, transiency and the initial intensity of the competing process are all systematically investigated. Multifrequency conversion is also found to be robust when the competing signal grows from a strong seed, as could arise from scattering of a pump beam.