Time Response Characteristics of Photodarkening-Induced Loss in Yb-Doped Fiber Amplifier

Photodarkening (PD) can degrade the output power and increase the thermal load in Yb-doped fiber lasers and amplifiers by increasing the propagation loss in the core [1,2]. PD can be attributed to color centers [3] and is reported to grow when the fiber is in use, over times from a few minutes to many hours (e.g., [2–4]). Typically, this is characterized in terms of a reduced output power of the operating device, but it is also possible to measure the transmission with non-resonant optical probes before, during, and after use. Although faster changes in the photodarkening are also possible [3], they have received little attention. Such fast changes can affect both the impact and the characterization of photodarkening.