Excited-state absorption in thulium-doped materials in the near-infrared

Abstract

Excited-state absorption (ESA) is a key process for upconversion pumping schemes of thulium (Tm³⁺) doped laser materials. We have systematically studied two ESA transitions in the near-infrared spectral range, namely ³F₄ → ³F_2,3 (at ∼1 µm) and ³F₄ → ³H₄ (at ∼1.5 µm), in various Tm³⁺-doped fluoride (ZBLAN glass, cubic KY₃F₁₀ and CaF₂, tetragonal LiYF₄ and LiLuF₄, monoclinic BaY₂F₈ crystals) and oxide (cubic Y₃Al₅O₁₂, orthorhombic YAlO₃ crystals) laser materials, using a pump-probe method with a polarized light. An approach to calculate the constants of energy-transfer upconversion (ETU) is also presented.