Nanoparticle doping and molten-core methods towards highly thulium-doped silica fibers for 0.79 µm-pumped 2 µm fiber lasers – A fluorescence lifetime study

in: Journal of Luminescence (2024)
Varak, Petr; Leich, Martin; Kamrádek, Michal; Aubrecht, Jan; Podrazký, Ondřej; Barton, Ivo; Svejkarova, Bara; Michalcova, Alena; Wondraczek, Katrin; Jäger, Matthias; Kasik, Ivan; Peterka, Pavel; Honzátko, Pavel
We study the fluorescence lifetime of Thulium-doped silica fibers for efficient laser operation in the 2 μm “eye-safe” wavelength range pumped by 0.79 μm radiation. A large set of optical fibers prepared by Modified Chemical Vapor Deposition combined with solution doping or nanoparticle doping, and Molten-core method is investigated in terms of fluorescence lifetimes of the 3 F4 and 3 H4 excited levels, which contain information about the Tm3+ ion environment, the rate of unwanted processes, such as concentration quenching or multiphonon relaxation, as well as the inter-ionic energy-transfer processes, including the cross-relaxation. Maximum evaluated lifetime values are 778 μs for the 3 F4 level and 56 μs for the 3 H4 level. From the lifetime study, we conclude that for Tm3+ concentrations above 10,000 ppm and enhanced aluminum concentrations above 5 mol. % Al2O3, the cross-relaxation efficiency is enhanced and multiphonon relaxation is remarkably reduced due to the lower phonon energy of the resulting alumino-silicate glass.

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