Short-Term and Long-Term Stability in Ytterbium-Doped High-Power Fiber Lasers and Amplifiers

In this paper we discuss recent progress in exploring short-term and long-term stability of high power Yb-doped fiber lasers and amplifiers. Long-term stability is associated with photodarkening effects that can significantly reduce operational lifetime of a high-power laser system. Short-term stability is associated with so-called transverse modal instabilities that degrade output beam quality at average powers above a certain threshold. In this paper we review ongoing studies that provide experimental characterization, and explore physical causes and mitigation strategies of the different physical phenomena involved. Those studies are critical for achieving stable operation of high power fiber lasers.