RESUMEN
A novel method for mitigating photo-darkening and the effective photo-bleaching phenomenon by 532â nm cladding pump in Yb-doped fiber were herein reported. Compared with the pristine fiber, beyond 30% of photo-darkening induced excess loss was suppressed by 532â nm pretreatment. Moreover, the excess loss in the photo-darkened fiber was completely bleached with 532â nm pump. Additionally, the bleached fiber exhibited better photo-darkening resistance. Therefore, for high power application, a 20/400 gamma irradiated fiber was bleached in situ by 532â nm pump and the laser properties were explored. The output power restored to 421W accounting for 82% of the pristine fiber, with the mode instability threshold rising to over 2.6 times and the efficiency increasing from 37% to 63%. The results indicate 532â nm pump has bright prospects for the stable operation of high power fiber lasers.
RESUMEN
A gain-tailored Ge-free Yb/Ce codoped aluminosilicate fiber is fabricated by MCVD combined with solution doping technique. Through regulating the temperature in the tube and designing the solution doping process, the refractive index profile of this fiber is close to a step-index without any center dip. The laser performance of this fiber is proved through contrast experiments with conventional fiber in a kW-level MOPA setup. The gain-tailored fiber amplifier presents a beam quality of M2 ~1.43 at 1.2 kW. Its MI threshold is 1.25 kW, about 1.74 times as much as that of the conventional fiber amplifier. The laser slope efficiency of the gain-tailored fiber amplifier is 86.75%. Stabilized at an output power of 1.1 kW for 15 hours, the MI threshold does not decrease after this long-term operation, demonstrating a strong resistance to photodarkening effect. These results have confirmed that MCVD-fabricated gain-tailored Yb/Ce codoped aluminosilicate fibers have great potential in power scaling and output stability of high-power fiber lasers and amplifiers.