Investigation of Photo-Darkening-Induced Thermal Load in Yb-Doped Fiber Lasers

We report on our investigation of photo-darkening (PD)-induced thermal load in Yb-doped fiber lasers and the effective suppression by H
₂
-loading. Compared with a quantum defect, the contribution of heat produced by PD was evaluated, indicating PD may become the primary heat source. To reduce the heat generation, the effect of H
₂
-loading on thermal load was quantitatively analyzed. The experimental results showed that 86% of PD loss was mitigated and 82% of PD-induced thermal load was eliminated by H
₂
-loading. In contrast, due to the presence of extra heat source, only 14% heat decreased in the Ce-doped fiber at similar PD loss level. The results indicate that H
₂
-loading is promising for further improving the stable operation of fiber lasers.