Efficient in-band pumped Ho:LuLiF4 2 mu m laser

An efficient Ho:LuLiF4 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:LuLiF4 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 (M2) was measured to be ~1.1 at the maximum output power confirming fundamental transverse mode (TEMoo) operation. The influence of resonator design on laser performance is discussed, along with prospects for further power scaling and improvement of the laser efficiency.