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.