Experimental investigations on the TMI thresholds of low-NA Yb-doped single-mode fibers.

In this contribution we investigate the transversal mode instability behavior of a ytterbium-doped commercial 20/400 fiber and obtain 2.9 kW of output power after optimizing the influencing parameters. In this context, we evaluate the influence of the bend diameter and the pump wavelength within the scope of the absorption length and the length of the fiber. Furthermore, with a newly developed fiber we report on 4.4 kW of single-mode output power at 40 cm bend diameter.