Hundred-watt-level cryogenic near diffraction-limited composite thin-disk Ho:YLF oscillator at 2 µm

We present a cryogenic composite thin-disk oscillator based on a holmium-doped yttrium lithium fluoride (Ho:YLF) crystal that we believe is for the first time, with a hundred-watt-level near diffraction-limited laser output. Integrating the multi-pass pumping configuration and the cryogenic cooling technique, a maximum power of 128 W was achieved with an optical efficiency of 62.5% at 2 µm. The spectroscopic properties of 2 at.% Ho:YLF at 80 K was systematically investigated, including fluorescence lifetime and emission cross section. The beam quality was measured to be M²_x = 1.55 and M²_y = 1.46 in the orthogonal directions.