Polarization switching in a mid-infrared Er:YAlO₃ laser

We report on a polarization-resolved study of mid-infrared emission properties of Er³⁺-doped orthorhombic yttrium aluminum perovskite YAlO₃ single crystal. For the ⁴I_11/2→ ⁴I_13/2 Er³⁺ transition, the stimulated emission cross section is 0.20 × 10^-20cm² at 2919 nm for light polarization E ‖ c. Pumped by an Yb-fiber laser at 976 nm, the 10 at.% Er:YAlO₃ laser delivered 1.36 W at 2919 nm with a slope efficiency of 31.4%, very close to the Stokes limit, a laser threshold as low as 33 mW and a linear polarization. Pump-induced polarization switching between E || b and E || c eigen states was observed and explained by excited-state absorption from the terminal laser level.