Polarized Mid-Infrared Emission Properties of Er3+ and Ho3+ Ions in YAlO3

Yttrium orthoaluminate (
$\text{YAlO}_{3}$
, shortly YAP) is a well-known laser host matrix for doping with rare-earth ions. It crystallizes in the same binary system as
$\mathrm{Y}_{3}\text{Al}_{5}\mathrm{O}_{12}$
but possesses an orthorhombic structure (sp. gr.
$\mathrm{D}{}_{2\mathrm{h}}^{16}$
-Pnma). Thus, YAP is an optically biaxial with anisotropic absorption / emission properties of the dopant ions leading to polarized laser emission. It features good thermal properties and low phonon energies which are essential for laser operation in the mid-infrared spectral range. Recently, efficient lasers based on
$\text{Er}^{3+}$
and
$\text{Ho}^{3+}$
-doped YAP crystals operating at
$\sim 3\mu \mathrm{m}$
according to the
${ }^{4} \mathrm{I}_{11 / 2} \rightarrow{ }^{4} \mathrm{I}_{13 / 2} \text{Er}^{3+}$
and
${ }^{5} \mathrm{I}_{6} \rightarrow{ }^{5} \mathrm{I}_{7} \text{Ho}^{3+}$
transitions, see Fig. 1(a), were demonstrated [1], [2]. Still, the information on the polarization anisotropy of stimulated-emission (SE) properties of these ions is scarce. In the present work, we report on polarized SE properties of
$\text{Er}^{3+}$
and
$\text{Ho}^{3+}$
-doped YAP crystals at
$\sim 3\mu \mathrm{m}$
.