Excited-state absorption (ESA) is a key process for upconversion pumping schemes of thulium (Tm) doped laser materials. We have systematically studied two ESA transitions in the near-infrared spectral range, namely F → F (at ∼1 µm) and F → H (at ∼1.5 µm), in various Tm-doped fluoride (ZBLAN glass, cubic KYF and CaF, tetragonal LiYF and LiLuF, monoclinic BaYF crystals) and oxide (cubic YAlO, orthorhombic YAlO 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.
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