Efficient fiber-laser pumped Ho:LuLiF 4 laser

We present results for an efficient Ho:LuLiF4 laser in-band pumped by a cladding-pumped Tm-doped silica fiber laser. The polarized, tunable Tm-doped silica fiber-laser operates at 1938 nm, ideally suited for in-band pumping the 40 mm long weakly-doped (0.25 at.%) Ho:LuLiF4 crystal. Using a simple laser resonator a maximum output power of 5.1 W was achieved at a wavelength of 2066 nm for 8.0 W of absorbed pump power, when using an output coupling mirror with 20% transmission, corresponding to a slope efficiency of 70%. At a higher cavity output coupling of 37%, the lasing wavelength shifted to a higher gain peak at 2053 nm, where a maximum output power of 5.4 W was obtained with a slope efficiency of 76%. Beam quality was measured to be M2~1.1 at the maximum output power for each resonator configuration. The spectroscopy, lifetime of the upper laser level, and the laser performance will be discussed in terms of future prospects for power scaling and further improvements in the laser efficiency.