Highly efficient resonantly pumped Er:YAG large area waveguide laser with diffraction limited output

We demonstrated nearly a quantum defect limited CW operation of a 41-mm-long Er:YAG large area crystalline waveguide laser with a diffraction limited output, which was resonantly pumped by a fiber laser at 1532 nm. Using a Er(0.25%):YAG, 62 μm x 62 μm waveguide, surrounded by a 3 x 5 mm rectangular cladding of undoped YAG, an output power of 9.1 W with slope efficiency of 92.8% has been achieved. The output laser beam had a Gaussian profile with a ~ 2.8 x 10^-2 rad divergence, which is in good agreement with the divergence expected from a waveguide with a low NA value. The waveguide laser operated simultaneously at two wavelengths, 1617 nm and 1645 nm, when the transmission of the laser cavity output coupler was less than 20-25%, and operated only at 1617 nm when the laser output mirror had a higher transmission.