Polarized spectroscopy and laser operation of Tm3+:YAlO3 crystal on the 3H4 → 3H5 transition

Yttrium orthoaluminate (YAlO₃) is an attractive laser host crystal for doping with thulium (Tm³⁺) ions. We report on the absorption and stimulated-emission (SE) cross-sections of this orthorhombic (sp. gr. Pnma) Tm:YAlO₃ crystal for the principal light polarizations, E || a, b and c. Polarized absorption data lead to the Judd-Ofelt parameters Ω₂ = 1.46, Ω₄ = 2.82 and Ω₆ = 1.09 [10^-20 cm²]. In particular, for the ³H₄ → ³H₅ transition, it is found a stimulated emission cross section of 0.86×10^-20 cm² at 2278 nm corresponding to an emission bandwidth of ~12 nm (for E || b). Continuous-wave laser operation on this ³H₄ → ³H₅ transition is achieved with an 1.8 at.% Tm:YAlO₃ crystal under laser-pumping at 776 nm. The mid-infrared Tm:YAlO₃ laser generated 0.96 W at ~2274 nm with a slope efficiency of 61.8% and a linear laser polarization (E || b). Tm:YAlO₃ is promising for mode-locked lasers at ~2.3 μm.