Upconversion pumping of a 2.3 µm Tm³⁺:KY₃F₁₀ laser with a 1064 nm ytterbium fiber laser

We report efficient lasing of the isotropic Tm^{3 +}:KY₃F₁₀ crystal near 2.3 µm via upconversion pumping with a 1064 nm ytterbium fiber laser as the pump source. When pumped at 1064 nm, an x-cavity Tm^{3 +}:KY₃F₁₀ laser operated at the free-running wavelength of 2344 nm. Lasing was obtained with output couplers having transmissions in the range of 1–3%, and as high as 124 mW of continuous-wave (cw) output power was generated with 604 mW of absorbed pump power by using the 3% output coupler. Broadly tunable cw lasing could be obtained in the 2268–2373 nm wavelength range. An analysis of the experimental power efficiency data shows that nearly all of the absorbed pump photons were converted to 2.3 µm laser output after accounting for the quantum defect of the laser transition and resonator losses. We expect that higher lasing efficiency should be possible by using longer crystals to increase the pump absorption.