Diode-pumped cryogenic Yb:KLu(WO<inf>4</inf>)<inf>2</inf> laser

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(WO 4 ) 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 Ng-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(WO 4 ) 2 (Yb:KLuW) at cryogenic temperatures pumped by a VBG-stabilized fiber coupled diode laser at 981 nm.