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2 μm lasers are in demand for a number of practical applications, such as environmental monitoring, remote sensing, medicine, material processing, and are also used as a pump sources for optical parametric generators. Crystals of double potassium tungstates doped with ions of rare-earth elements were shown to be promising materials both for  the  creation  of  classical  solid-state  lasers  and  waveguide  lasers. The aim of this work was to develop a tunable pump laser in the spectral region of 1.9 µm based on double tungstate crystals doped with thulium ions and to study the lasing characteristics of a Ho:KY(WO4)2 crystal and a Ho:KGdYbY(WO4)2 single-crystal epitaxial layer under in-band pumping.With a Ho(1at.%):KY(WO4)2  crystal, continuous wave low-threshold lasing with an output power of 85 mW with a slope efficiency of 54 % at 2074 nm was achieved. For the first time to our knowledge, continuous wave laser  generation  in  a  waveguide  configuration  is  realized  in  a  single-crystal  layer of potassium tungstate doped with holmium ions grown by liquid-phase epitaxy. The maximum output power at a wavelength of 2055 nm was 16.5 mW.

We report on the composition of Er-doped KGdYbY(WO) layers to be grown onto undoped KY(WO) substrate providing fine lattice matching and high refractive index contrast with the substrate and fabrication of high optical quality Er(1.3  at. %):KGdYbY(WO) epitaxial layers with thickness up to 180 μm. Absorption and luminescence properties of the layer were measured and laser action under direct in-band pumping was reported for the first time, to our knowledge, in a non-waveguide configuration. A maximum output power of 16 mW with slope efficiency of 64% was achieved at 1606 nm.

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