Continuous-wave 2.3-µm Tm³⁺:Lu₂O₃ ceramic laser with ultrabroad tunability between 1845 nm and 2328 nm

We report, for the first time to our knowledge, a 2.3-µm continuous-wave (CW) laser operation of trivalent thulium ion (Tm³⁺)-doped Lu₂O₃ ceramic. In the free-running laser operation, co-lasing could be observed at the wavelengths of 2096 nm and 2325 nm. The laser operation and power performance of the ³F₄→³H₆ and ³H₄→³H₅ transitions were investigated separately with a birefringent tuning plate. By using a double-end-pumped x-cavity, 134 mW of CW output power was obtained at the wavelength of 2309 nm with 4 W of pump power and with 7% slope efficiency. By using two sets of cavity optics, we further achieved the broadest, continuous tuning range, obtained to date for a Tm³⁺ laser, extending from 1845 nm to 2328 nm. We also investigated a 2-µm laser operation, where with a 1.3% output coupler, a maximum CW output power of 917 mW was obtained at 2094 nm with 3.93 W of pump power. By using the laser threshold and power efficiency data measured during the 2.3-μm operation, the emission cross section of the Tm³⁺:Lu₂O₃ ceramic gain medium was determined to be 3.24 × 10^-21 cm² at the wavelength of 2309 nm.