Forster, PatrickPatrickForsterPanitzek, DieterDieterPanitzekRomano, ClémentClémentRomanoLorenz, DominikDominikLorenzSchneider, JulianJulianSchneiderEichhorn, MarcMarcEichhornKieleck, ChristelleChristelleKieleck2023-09-072023-09-072023https://publica.fraunhofer.de/handle/publica/45037710.1109/cleo/europe-eqec57999.2023.10232508Efficient high-power lasers emitting at a wavelength of around 2.12 μm are of increasing interest for applications taking advantage of a broad atmospheric transmission window. Typically, Ho 3+ -doped fiber lasers (HDFL) are used to address this wavelength region due to much higher emission cross sections compared to their 2 μm equivalent Thulium lasers [1], [2]. Recently, Tm 3+ :Ho 3+ -codoped fiber lasers were demonstrated with a slope efficiency as high as 56 % [3] and output powers up to 260 W [4], thus making them a sound substitute to HDFLs for operation above 2.1 μm . The free-space setup shown in [4] is now transferred to a more integrated and rugged all- fiber version. To the best of our knowledge, we show the first realization of a Tm 3+ :Ho 3+ -codoped all-fiber laser emitting at 2120 nm with a slope efficiency close to 50 %.enconference paper