Broadly tunable continuous-wave Tm:CALYO laser operating on the 3H4→3H5 transition.

We report broadly tunable diode-pumped laser operation of a disordered Tm:CALYO aluminate crystal on the 3H4 → 3H5 transition. By applying an intracavity birefringent filter, continuous tuning ranges of 258 nm (2254-2512 nm) and 225 nm (2235-2460 nm) were achieved for the π- and σ-polarized eigen polarization states of this uniaxial crystal, respectively. In the free-running regime, the Tm:CALYO laser delivered a maximum continuous-wave output power of 1.10 W at 2.3 µm with a slope efficiency of 6.4%. The polarized spectroscopic properties of Tm3+ ions in CALYO were systematically investigated to explain the observed laser behavior. The stimulated-emission cross section for π-polarized light reaches 0.23 × 10-20 cm2 at 2353 nm, corresponding to an emission bandwidth exceeding 250 nm, while the intrinsic luminescence lifetime of the 3H4 upper laser level is about 400 µs. Attention was devoted to crystal annealing conditions, which were found to play a critical role in optimizing laser performance and represent a pathway for further improvement. Owing to its exceptionally broad emission bandwidth and good thermal properties, Tm:CALYO emerges as a promising gain material for femtosecond pulse generation at 2.3-2.4 µm.