Broadly tunable continuous wave 2.3-µm Tm³⁺:tellurite bulk glass laser

We report, for the first time to the best of our knowledge, a continuous wave trivalent thulium ion (Tm³⁺)-doped bulk glass near 2.3 µm. In the experiments, a bulk Tm³⁺-doped tellurite glass with the stoichiometric composition of 74TeO₂-12ZnO-4La₂O₃-10Na₂O (Tm³⁺:TZLN) was used. Lasing operation was achieved by using an x-fold cavity at the free-running wavelength of 2303 nm. The maximum slope efficiency of 6.2% was obtained with respect to the absorbed pump power with a 1% transmitting output coupler. In this case, as high as 100-mW output power was generated with 2.2 W of absorbed pump power. Continuous, broad tuning was achieved from 2233 nm to 2400 nm. The excitation spectrum of the laser was also investigated and 2.3-µm lasing was obtained by varying the pump wavelength over the 773-809-nm range. The absorption cross section was determined to be 4.4 × 10^-21 cm², based on open-aperture z-scan measurement. By using the laser efficiency data, the emission cross section of the Tm³⁺:TZLN glass was further determined to be 1.3 × 10^-20 cm² at 2.3 µm.