Close look on cubic Tm:KY3F10 crystal for highly efficient lasing on the 3H4 → 3H5 transition

We report on Czochralski growth, detailed ground- and excited-state absorption and emission spectroscopy and highly-efficient mid-infrared (∼2.3 µm) laser operation of a cubic potassium yttrium fluoride crystal, Tm:KY 3 F 10 . The peak stimulated-emission cross-section for the 3 H 4 → 3 H 5 ransition is 0.34×10 -20 cm 2 at 2345 nm with an emission bandwidth exceeding 50 nm. The excited-state absorption spectra for the 3 F 4 → 3 F 2,3 and 3 F 4 → 3 H 4 ransitions are measured and the cross-relaxation is quantified. A continuous-wave 5 at.% Tm:KY 3 F 10 laser generated 0.84 W at 2331-2346 nm by pumping at 773 nm, with a record-high slope efficiency of 47.7% (versus the incident pump power) owing to the efficient action of energy-transfer upconversion leading to a pump quantum efficiency approaching 2. The first Tm:KY 3 F 10 laser with ESA-assisted upconversion pumping (at 1048 nm) is also demonstrated. Due to its broadband emission properties, Tm:KY 3 F 10 is promising for ultrashort pulse generation at ∼2.3-2.4 µm.