Hundred-watt-level high-brightness multimode fiber laser

High-power fiber lasers are widely used in various fields due to their high efficiency, flexible light transmission, and excellent beam quality. Further power enhancement in fiber lasers is hindered by two critical issues: nonlinear effects and the transverse mode instability effect. To address this bottleneck, a promising strategy is to utilize multimode fibers combined with wavefront shaping techniques. Multimode fibers alleviate the nonlinear constraints while the wavefront shaping techniques convert the output speckle beam profile into a single concentrated spot to ensure brightness. However, to date, the performance of high-power multimode fiber laser systems based on wavefront shaping schemes has not been systematically investigated, and the average power of demonstrations based on this scheme remains at the watt level. To explore the feasibility of this scheme under a high-power regime, a high-power multimode fiber laser amplifier based on wavefront shaping is constructed and investigated in this study. The system achieves a focused beam profile at 168 W output power, demonstrating an eightfold brightness enhancement compared to the uncontrolled state. The design of the objective function and the effects of wavefront shaping on fiber coupling and of the seed laser linewidth on the system performance are also investigated. This work provides a reference for further exploring the potential of multimode fibers in improving the brightness of fiber lasers.