2.08 µm Ho:KLu(WO4)2 laser resonantly pumped by a diode laser

Infrared solid-state lasers based on the Ho³⁺ (Ho) ion operating slightly above 2 μm have potential applications in the fields of medicine, remote sensing and as pump sources for OPOs. A serious limitation with regard to all-solid-state systems is that the Ho ion does not exhibit suitable absorption features that match the existing commercial diodes and hence many researchers used Tm as sensitizer. However, up-conversion losses in the Tm ions lead to poor efficiency of the ⁵I₇ → ⁵I₈ transition in Ho. On the contrary, direct excitation of the ⁵I₇ level of Ho around 1.9 μm offers advantages to achieve higher efficiencies and higher output powers due to minimal thermal load. This is the ultimate solution for power scaling of Ho lasers. Many fluoride and oxide crystals were shown to be suitable as Ho hosts but little attention was paid to the monoclinic double tungstates with general formula KRE(WO₄)₂ (KREW) where RE=(Y, Gd, Lu), known as very efficient laser hosts at intermediate power levels. In this work we demonstrate continuous-wave (CW) laser action of Ho in KLuW crystal near 2.08 μm at room temperature using in-band pumping by recently developed laser diodes operating in the 1.9 μm range. The laser performance is compared with the other members of the same family of crystals.