Near diffraction-limited in-band pumped Ho:YLF composite thin disk laser at 2 μm

A room-temperature composite thin disk laser is demonstrated based on a holmium-doped yttrium lithium fluoride (Ho:YLF) crystal. The composite thin disk structure was proposed and designed to enhance mechanical strength and suppress the ASE effect. The spectroscopic properties, including emission cross-section and fluorescence lifetime, of the 2 at.% doped Ho:YLF were investigated. In-band pumped by a 1940nm Tm-doped fiber laser, the system achieved a CW output of 26.5 W with a slope efficiency of 42.0%. The beam quality was near-diffraction-limited, with M²_x = 1.12 and M²_y = 1.09. This work demonstrates the potential of Ho:YLF composite thin disk lasers for high-quality, stable operation at 2 μm. To the best of our knowledge, this is the first report of a Ho:YLF composite thin disk laser at room temperature.