A 2 mu m holmium laser

A comparison of the CW laser performance of the /sup 5/I/sub 7/-/sup 5/I/sub 8/ transition at 2 mu m in erbium-thulium-sensitized Ho:YLF and Ho:YAG ( alpha beta Ho:YLF and alpha beta Ho:YAG) crystals at liquid nitrogen temperature is reported. Multimode-laser output power above 60 W was obtained with two compositions of alpha beta Ho:YLF (with a rod size of 5 mm in diameter and 75 mm in length) with 4.1% efficiency and 4.75% slope efficiency. Thermal load measurements on alpha beta Ho:YLF and alpha beta ZHo:YAG laser rods and effects of the pumping lamp on the laser yield are presented. Preliminary results on single-pulse operation of both alpha beta Ho:YLF and alpha beta Ho:YAG lasers in free-running mode threshold in both YLF and YAG is constant up to 100 K and increases with temperature above 11 degrees K. The laser slope efficiency in YAG is constant up to 150 K, above which it decreases with temperature, while in the ULF the slope efficiency has a broad maximum around 150 K. The net result in YLF is a broad maximum of the laser output power around 130 K at high pumping levels. >