2.1 μm composite Tm/Ho:YAG laser.

We realize Ho laser operation in a composite Tm/Ho:YAG gain medium for the first time, to the best of our knowledge, which was integrated via diffusion bonding the Tm-doped and Ho-doped crystals into a single bulk structure. A maximum output power around 6 W was obtained with a slope efficiency of 40.1% and conversion efficiency (CE) of 33.6% from the absorbed 785 nm laser diode to 2122 nm Ho laser, which is comparable with CE in 1.9 μm LD pumped Ho lasers. Such a scheme is demonstrated to be another valid way for Ho laser generation here, which is of significance to be adopted in other host media or waveguide structures for an assessable, compact, and efficient Ho laser.