Determination and Analysis of Line-Shape Induced Enhancement of Stimulated Brillouin Scattering in Noise Broadened, Narrow Linewidth, High Power Fiber Lasers

We investigate the origin of line-shape induced enhancement stimulated Brillouin scattering (SBS) in narrow linewidth, noise broadened, high-power fiber lasers. A polarization-maintaining seed laser with continuously tunable linewidth (single frequency to >10 GHz), based on white modulation was developed for this study. With increasing linewidths, a substantial difference SBS thresholds observed depending end termination utilized. This observation can be explained by line-broadened source, having significant power Stokes at larger seeding process. Here, threshold system terminated an anti-reflection coated delivery cable is compared simple angle cleaved termination. The influence becomes increased showing >20% output between two cases ~10 GHz linewidth. experiments are complemented simulations, analyzing relative contributions Rayleigh and end-facet reflections SBS. At due overlap Stokes, low reflectivity, dominant mechanism, which gives way reflectivity. contribution negligible smaller reflectivity has weaker than linewidths.