Holmium thin-disk laser based on Ho:KY(WO₄)₂/KY(WO₄)₂ epitaxy with 60% slope efficiency and simplified pump geometry

We report on the first holmium (Ho³⁺) monoclinic double tungstate thin-disk laser. It is based on a 250 μm thick 3 at. % Ho:KY(WO₄)₂ active layer grown on a (010)-oriented KY(WO₄)₂ substrate. When pumped by a Tm-fiber laser at 1960 nm with a single-bounce (single double-pass) pump geometry, the CW Ho:KY(WO₄)₂ thin-disk laser generated 1.01 W at 2057 nm, corresponding to a slope efficiency η of 60% and a laser threshold of only 0.15 W. Implementing a double-bounce (second double-pass) for the pump, the output of this laser was scaled to 1.57 W with η=55%. The maximum stimulated emission cross section σ_SE of the Ho³⁺ ions in the epitaxial layer reaches 2.5×10^-20  cm² at 2056.5 nm for E‖N_m. The Ho:KY(WO₄)₂ epitaxial structures are promising for multi-watt mode-locked thin-disk lasers at ∼2.06  μm.