Emission properties of Tm3+-doped CaF2, KY3F10, LiYF4, LiLuF4 and BaY2F8 crystals at 1.5 μm and 2.3 μm

Abstract

Thulium ions (Tm3+) are known for their emissions in the near- and mid-infrared spectral ranges suitable for efficient laser operation. We systematically study the stimulated-emission crosssections σSE for the 3H4 → 3F4 (at ~1.5 μm) and 3H4 → 3H5 (at ~2.3 μm) Tm3+ transitions in five low-phonon energy fluoride singlecrystals, namely, cubic Tm:CaF2 and Tm:KY3F10, tetragonal Tm:LiYF4 and Tm:LiLuF4 and monoclinic Tm:BaY2F8. A promising material is Tm:BaY2F8 which offers broad and intense polarized emission spectra in the mid-infrared (2251–2452 nm); the maximum σSE is 0.39 × 10−20 cm2 at 2289 nm (for E ||Z) and the emission bandwidth is exceeding 100 nm (for E ||X). We also revise the transition probabilities for Tm3+ ions in LiLuF4 and BaY2F8 crystals using the Judd-Ofelt formalism and accounting for an intermediate configuration interaction (ICI).