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 (Tm 3+ ) doped laser materials. We have systematically studied two ESA transitions in the near-infrared spectral range, namely 3 F 4 → 3 F 2,3 (at ∼1 µm) and 3 F 4 → 3 H 4 (at ∼1.5 µm), in various Tm 3+ -doped fluoride (ZBLAN glass, cubic KY 3 F 10 and CaF 2 , tetragonal LiYF 4 and LiLuF 4 , monoclinic BaY 2 F 8 crystals) and oxide (cubic Y 3 Al 5 O 12 , orthorhombic YAlO 3 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.