ИСТИНА

MgWO4 has recently emerged as a suitable host for doping with rare-earth ions (RE3+) such as Yb3+, Tm3+, Er3+ or Ho3+ for applications in mode-locked lasers. MgWO4 belongs to the monoclinic class (sp. gr. P2/c); RE3+ dopant ions replace Mg2+ cations in a single type of sites (C2 symmetry). RE3+:MgWO4 crystals combine good thermo-mechanical properties of the host and attractive spectroscopic behavior of the RE3+ ions (intense and broad spectral bands for polarized light, large Stark splitting of the ground state). Up to now, the information about the anisotropy and dispersion of MgWO4 refractive indices is unavailable. However, it is a critical parameter for calculation the design of lasers optical schemes. The aim of our research was to fill this information gap. MgWO4 single crystal of was obtained by top seed solution growth method from Na2WO4 flux. The as-grown crystal was dark-red colored due to an uncontrolled Fe impurity; it was without cracks, growth striations and second phase precipitates. For refraction indices measurements, two prisms were cut from the MgWO4 boule with their input faces oriented along the (010) and (001) planes. MgWO4 is optically biaxial. Its optical properties are characterized in the frame of the optical indicatrix with three principal axes, Np, Nm and Ng. Nm is parallel to the b crystallographic axis, while another two ones are lying in a-c crystallographic plane. The angle between Np and c crystallographic axis is 37.1°, measured within the monoclinic angle β. The refractive indices were measured by the normal incidence method. MgWO4 has a high refractive indices and a strong natural birefringence, np = 1.981, nm = 2.016 and ng = 2.167 at 1064 nm. Single-pole Sellmeier equations are proposed to describe the material dispersion. Further work will focus on measuring the thermo-optic coefficients of MgWO4 for describing its expected “athermal” behavior.