Efficient in-band pumped Ho:LuLiF_4 2 μm laser

An efficient Ho:LuLiF_4 laser in-band pumped by a cladding-pumped Tm-doped silica fiber laser operating at 1937 nm is reported. At low-cavity output coupling, the Ho:LuLiF_4 laser yielded 5.1 W of output at a wavelength of 2066 nm for 8.0 W of absorbed pump power with a slope efficiency of 70%. At high-cavity output coupling, the lasing wavelength shifted to 2053 nm and the laser produced an output power of 5.4 W with a slope efficiency of 76%. The beam propagation factor (M^2) was measured to be ~1.1 at the maximum output power confirming fundamental transverse mode (TEM_oo) operation. The influence of resonator design on laser performance is discussed, along with prospects for further power scaling and improvement of the laser efficiency.