Near-diffraction-limited femtosecond laser based on ytterbium-doped yttrium aluminum garnet rod-type amplifiers with approximately 500 W average power and more than 50% power extraction efficiency

Abstract A high-power, efficient pulsed amplifier based on a laser diode end-pumped ytterbium-doped yttrium aluminum garnet (Yb:YAG) rod was demonstrated. The crystal’s reabsorption was effectively minimized by optimizing the amplifier’s parameters through numerical simulations, leading to a power extraction efficiency of up to 56%. A compensation method was applied to correct the beam distortion caused by thermally induced birefringence in the Yb:YAG rod. Furthermore, a remarkably low depolarization rate of 2.2% was achieved, along with an average power output of 483 W. The beam quality factor ( M 2 ) of the amplified signal was improved to below 1.3, following compensation of the thermally induced spherical aberration using a phase plate. To the best of our knowledge, this achievement represents the highest average power and efficiency for fundamental mode operation in an Yb:YAG rod amplifier at room temperature.