Mid-infrared erbium waveguide laser with efficiency beyond the quantum-defect limit

We report a watt-level mid-infrared erbium-depressed-cladding waveguide laser operating beyond the quantum-defect limit. A 10 at.% Er³⁺-doped orthorhombic YAlO₃ single crystal was micro-structured by ultrafast-laser inscription, yielding strong refractive-index modulation (-2.6 × 10^-3) and low propagation losses (0.12 dB/cm). Under 976-nm pumping, the waveguide laser generated up to 1.12 W of linearly polarized output at 2920 nm, with a slope efficiency of 36.7% and an exceptionally low laser threshold of 15 mW. These outstanding performances demonstrate the strong potential of this platform for compact and power-scalable mid-infrared light sources.