Dispersion and anisotropy of thermo-optic coefficients in tetragonal GdVO4 and YVO4 laser host crystals

A detailed experimental study of dispersion and anisotropy of thermo-optic coefficients dn/dT and thermal coefficients of the optical path W = dn/dT + (n - 1)alpha is performed for tetragonal YVO4 and GdVO4 laser host crystals by a laser beam deviation method. It is supported by theoretical description of thermo-optic effects, taking into account the volumetric thermal expansion effect and the temperature dependence of electronic bandgap E-g. Linear thermal expansion coefficients a were also determined by a dilatometric technique. Thermo-optic dispersion formulas describing temperature variation of the refractive index and the thermal lens effect are derived for a wide spectral range of 0.4-2 mu m. It allows us to estimate the values of Eg and dEg/dT for the studied crystals. The influence of materials parameters and pumping conditions on thermal lens properties is discussed, revealing the significant impact of anisotropic and temperature-dependent thermal conductivity. (C) 2013 Optical Society of America