Effect of intensity noise on stimulated Raman scattering in high power fiber lasers and amplifiers

Stimulated Raman Scattering is one of the primary nonlinearities limiting power scaling of high power fiber lasers and amplifiers. Conversion of signal light into the Raman generated Stokes component can result in several undesirable consequences such as temporal instabilities, spurious pulsing, beam quality degradation, focusing errors etc. most of which are catastrophic for the laser system. In this work, we investigate a novel and important aspect of Raman scattering in fiber lasers and amplifiers. Owing to intrinsic intensity noise at high powers, we demonstrate that the actual Raman gain can be substantially higher than the expected values calculated from mean powers. Using a physical model for intensity noise, we demonstrate very interesting connections between the laser bandwidth, dispersion in fiber and the actual Raman gain. This work enables further power scaling by providing design methodologies to control Raman scattering in fiber lasers and amplifiers.