Efficient in-band pumped Ho:LuLiF_4 2 μm laser

Abstract

An efficient $\mathrm{Ho}:\mathrm{Lu}\mathrm{Li}{\mathrm{F}}_4$ laser in-band pumped by a cladding-pumped Tm-doped silica fiber laser operating at $1937\mathrm{nm}$ is reported. At low-cavity output coupling, the $\mathrm{Ho}:\mathrm{Lu}\mathrm{Li}{\mathrm{F}}_4$ laser yielded $5.1\mathrm{W}$ of output at a wavelength of $2066\mathrm{nm}$ for $8.0\mathrm{W}$ of absorbed pump power with a slope efficiency of 70%. At high-cavity output coupling, the lasing wavelength shifted to $2053\mathrm{nm}$ and the laser produced an output power of $5.4\mathrm{W}$ with a slope efficiency of 76%. The beam propagation factor $\left({\mathit{M}}^2\right)$ was measured to be $\sim 1.1$ at the maximum output power confirming fundamental transverse mode $\left({\mathrm{TEM}}_{\mathrm{oo}}\right)$ operation. The influence of resonator design on laser performance is discussed, along with prospects for further power scaling and improvement of the laser efficiency.