Investigations on High Power Oscillators and Amplifiers Based on Birefringent Yb:LiLuF4 Single Crystal Fibers Grown by the Micro Pulling Down

In this talk, we will present our latest results obtained both in multi-pass amplification and laser oscillation, by pumping a 2%-doped, 42-mm long Yb:LiLuF4 SCF with a 135-W laser diode at 976 nm. For the amplification experiments we employed either a 1-W cw seeder, or a 150-μJ, 100-ns PQS seeder at 5 kHz repetition rate. Four passes small signal gain G0~40 was achieved at ~85 W of absorbed pump power with a maximum output power of 8 W in cw experiments and a 1- mJ amplified pulse energy, when seeding with the PQS laser. In both cases, diffraction limited beam quality was obtained at the maximum pump power. In laser oscillator experiment, we achieved up to 25 W, with M2~2 and ~40% slope efficiency in a simple confocal resonator layout