Watt-level diode-pumped Tm³⁺-doped sesquioxide crystals laser operating on the ³H₄→³H₅ transition at 2.3 µm

Tm³⁺-doped sesquioxide crystals represent promising gain media for 2.3 µm lasers owing to their low phonon energy and high thermal conductivity. However, the difficulty in obtaining high-quality crystals and the underdeveloped analysis of energy-transfer upconversion (ETU) processes significantly limit their application in the field of 2.3 µm lasers. To address the crystal quality challenge, we successfully grew Tm:Lu₂O₃ and Tm:LuYO₃ crystals with dimensions of Φ6 × 20-30 mm using the laser floating zone (LFZ) method. Subsequently, we investigated their laser performance at 2.3 µm. Under 793 nm wavelength-locked laser diode (LD) pumping and based on the ³H₄→³H₅ transition, continuous-wave (CW) 2.3 µm laser operation was demonstrated. The Tm:Lu₂O₃ crystal achieved a maximum output power of 1.1 W with a slope efficiency of 21.7%, while the Tm:LuYO₃ crystal yielded 1.0 W with a slope efficiency of 21%. To the best of our knowledge, these results represent the highest output powers achieved to date from sesquioxide crystals under LD pumping at 2.3 µm and also proves the potential for application in the 2.3 µm band.