Experimental characterization of a continuous-wave Tm³⁺:LiYF₄ waveguide laser simultaneously operating at 1.9 µm and 2.3 µm with 1.8 W of output

We provide a detailed experimental characterization of watt-level continuous-wave (CW) operation of a co-lasing Tm³⁺:LiYF₄ channeled waveguide laser at 1.9 µm and 2.3 µm. Waveguide fabrication was performed by femtosecond laser direct writing. Two Tm³⁺:LiYF₄ crystals with 1 at. % and 2 at. % Tm³⁺ doping were compared by inscribing 70-µm-diameter and 100-µm-diameter channeled waveguides. The best co-lasing power performance was obtained with a 100-µm-diameter waveguide inside the 1 at. % Tm³⁺:LiYF₄ crystal by using resonator mirrors with an effective output coupling of 30.2% at 1.9 µm and 3.2% at 2.3 µm. In this configuration, output powers of 1.12 W and 692 mW were generated at 1.9 µm and 2.3 µm, resulting in a total CW output power of 1.8 W with 4 W incident pump power, and a total slope efficiency of 46.7% with respect to incident power. The central lasing wavelengths were measured as 1881 nm and 2305 nm. The experimental co-lasing power efficiency data were further analyzed with a rate-equation model by accounting for cross relaxation and energy transfer upconversion, and simulations were performed to investigate the variation of the co-lasing threshold pump power as a function of doping concentration.