Experimental investigation of laser operation in a depressed cladding Tm³⁺:KY₃F₁₀ waveguide laser near 2.3 µm and 1.9 µm

We present a detailed investigation of a femtosecond laser written depressed cladding Tm³⁺:KY₃F₁₀ waveguide laser at 2.3 µm and 1.9 μm. Lasing of the Tm³⁺:KY₃F₁₀ channeled waveguide at 2.3 μm was demonstrated for the first time. A circular depressed cladding waveguide with a core diameter of 70 µm was fabricated inside an 8 at. % Tm³⁺:KY₃F₁₀ crystal by femtosecond laser writing. The fabricated waveguide had a measured propagation loss of 0.55 dB/cm and refractive index contrast of 9.5 × 10^-4. Using a Yb-fiber laser operating at 1064 nm as the pump source and a 4 % output coupler, upconversion pumped waveguide laser operation was achieved at 2331 nm with a power slope efficiency of 6.3 %. With a different set of cavity optics and a 33 % output coupler, upconversion pumped waveguide laser operation was also demonstrated near 1.9 µm, where as high as 303 mW of continuous-wave power was generated at 1849 nm with 2 W of pump power and power slope efficiency of 17.7 %. The temporal stability of the waveguide laser was high with a power fluctuation of only 0.2 % over one hour. Passively Q-switched operation was further obtained with a Cr:ZnSe saturable absorber at 1852 nm, giving 110 mW of average output power, power slope efficiency of 6.7 % and pulses as short as 22.4 ns at a pulse repetition rate of 11 kHz, yielding a peak power as high as 448 W.