Evidence of photodarkening mitigation in Yb-doped fiber lasers by low power 405 nm radiation

In this letter, we investigate the impact of a 405 nm radiation on photodarkening generation in Yb- doped fiber laser. Simultaneous photodarkening and photobleaching effects induced by 976 and 405 nm radiations, respectively, were investigated in a 1070 nm laser and compared with the loss induced in an irradiated active fiber. We observed a significant photobleaching effect due to 405 nm radiation but not a complete recovery. A strong absorption of the 405 nm radiation by the excited ions was also observed and could be the limiting factor for the bleaching performance. We also observed for the first time, to the best of our knowledge, ground-state absorption induced photodarkening in pristine fiber irradiated at 405 nm. This effect could generate additional residual losses in the laser system.