Abstract

In recent years, the development of compact all solid-state lasers has attracted the scientific community because of their vast scientific and technological applications. In particular, ytterbium (Yb³⁺) laser sources have been developed with a great number of hosts, due to the promise of the Yb³⁺ ion related to the very simple energy level structure and absence of higher energy levels, as well as a small quantum defect. However, at room temperature (RT) these materials behave as quasi three-level lasers due to a finite population of the ground state leading to reabsorption limited power scaling [1]. To overcome this issue, the material has to be cooled to cryogenic temperatures, where four-level operation is accomplished. The monoclinic potassium lutetium double tungstate crystal, KLu(WO₄)₂, considered here exhibits favourable spectroscopic properties when doped with Yb³⁺, characterized by large absorption and stimulated-emission cross sections and attractive thermo-optic properties for certain “athermal” crystal cuts (e.g., along the N_g-axis). It is very suitable for moderate power levels as demonstrated with Yb³⁺ and Tm³⁺ doping at RT [2]. In this work, we studied the continuous-wave laser characteristics of Yb:KLu(WO₄)₂ (Yb:KLuW) at cryogenic temperatures pumped by a VBG-stabilized fiber coupled diode laser at 981 nm.

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