25 W continuous-wave Yb:LiLuF4 single-crystal-fiber laser oscillator

We present the first demonstration of a solid-state laser oscillator based on a Yb-doped, birefringent single crystal fiber grown by the micro-pulling-down method. Pumping a 42-mm-long, 2%-at. Yb3+:LiLuF4 crystal with a 105-W maximum power fiber coupled laser diode, we obtained a maximum output power of 10.4 W, with diffraction limited beam quality (M2<1.1), in a simple plane-concave resonator. By modifying the resonator layout to increase the laser efficiency, we obtained output power up to 25 W, with still fairly good beam quality (M2?2). Thermal lensing effect and laser intrinsic slope efficiency and losses were characterized in both resonator configurations. © 2021 Elsevier B.V.