Power Scaling of Diffraction-Limited, Narrow-Linewidth Fiber Lasers to Beyond 10 kW

Power scaling of near-diffraction-limited fiber lasers to the multi-kW level, especially with narrow linewidth, requires the suppression of a wide range of parasitic phenomena. This includes deleterious processes such as stimulated Brillouin and Raman scattering, which originate from nonlinear interactions with hypersonic acoustic and optical phonons, respectively. Transverse mode instability, an obstacle to maintaining good beam quality at high power, stems from the thermo-optic effect. Furthermore, as power scales, so too does the thermal load on the active fiber, necessitating more effectual removal of heat from the system. Finally, the fiber must be resistant to long-term photo-induced degradation. Approaches to managing these deleterious processes at high power are discussed, including targeted glass design used to optimize the magnitude of those material coefficients that drive these limitations.