Gamma Radiation-Induced Darkening Effect on Ytterbium-Doped Fiber Oscillators

Under gamma irradiation, the output power of the fiber laser gradually decreases due to the rise of radiation-induced attenuation (RIA) also known as the radiation-induced darkening effect. This phenomenon may lead to a decreased threshold of transverse mode instability, reducing the stability and beam quality of the fiber lasers. Understanding the darkening effect on fiber lasers, particularly high-power oscillators, is necessary. This work comprehensively investigates the irradiation effect on the ytterbium-doped fiber (YDF) oscillator operating at around 200 W online and the annealing process afterward. During the irradiation process, we find that the RIA of the rare-earth-doped fiber increased linearly with the total radiation dose, due to the generation of color centers. The output power of the 1060-nm oscillator decreased by nearly 12% after 6 krad(Si) irradiation, which recovered to 90.6% after annealing for 15 min. For the 1080-nm oscillator, its power dropped by almost 13% under 3 krad(Si) irradiation, recovering to 91.2% after 30-min annealing. We further constructed a rate equation model and calculated the radiation sensitivity of the fiber irradiation position and fiber pumping scheme. We find that the radiation-resistant performance of the backward pumping is better than that of the forward pumping. Our result is valuable to understand the radiation-induced darkening effect and for the development of radiation-resistant fiber lasers.