Watt-level diode-pumped Tm-doped sesquioxide crystals laser operating on the H→H transition at 2.3 µm.

Tm-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:LuO and Tm:LuYO 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 H→H transition, continuous-wave (CW) 2.3 µm laser operation was demonstrated. The Tm:LuO crystal achieved a maximum output power of 1.1 W with a slope efficiency of 21.7%, while the Tm:LuYO 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.