Hundred-watt-level phosphosilicate Raman fiber laser with less than 1% quantum defect

Quantum defect (QD)-induced high thermal load in high-power fiber lasers can largely affect the conversion efficiency, pose a threat to the system security, and even prohibit the further power scaling. In this Letter, we investigate evolutions and influences of the reflectivity of the output coupler, the length of phosphosilicate fiber, and the pump bandwidth, and demonstrate a hundred-watt-level low-QD Raman fiber laser (RFL). The RFL enabled by the boson peak of phosphosilicate fiber achieves a maximum power of 100.9 W with a reduced QD down to 0.97%; the corresponding conversion efficiency reaches 69.8%. This Letter may offer not only an alternative scheme for a high-power, high-efficiency fiber laser, but also great potential on the suppression of thermal-induced effects such as thermal mode instability and the thermal lens effect.