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.