Thulium-doped channel waveguide laser with 1.6 W of output power and exceeding 80% slope efficiency

Dielectric channel waveguide lasers are of great interest because of their low pump thresholds and, even more so, high slope efficiencies resulting from the excellent overlap between pump and laser modes and the small transverse channel cross-sections which reduce the volume of active medium that needs to be pumped. Slope efficiencies up to 75% in a femtosecond-written YAG:Yb³⁺ channel waveguide with an output power of 800 mW [1], 76% in a LiYF₄:Tm³⁺ planar waveguide with an output power of 560 mW [2], as well as 70% and 76% in Tm³⁺ - and Yb³⁺ -doped potassium double tungstate channel waveguides with output powers of 300 mW [3] and 650 mW [4], respectively, are state of the art.