Influence of Temperature on Refractive Indices of BaLaGa$\text{}_{3}$O$\text{}_{7}$ and SrLaGa$\text{}_{3}$O$\text{}_{7}$

A simple theoretical approach based on Kramers-Krönig relations predicts well the dispersion and birefringence of BaLaGa$\text{}_{3}$O$\text{}_{7}$ and SrLaGa$\text{}_{3}$O$\text{}_{7}$. In the whole transparency region the birefringence of both compounds is too low to offset dispersion in the process of a second harmonic generation, thus the crystals cannot be made phase matchable. Birefringence of BaLaGa$\text{}_{3}$O$\text{}_{7}$ and SrLaGa$\text{}_{3}$O$\text{}_{7}$ is stable with respect to the temperature region of 300-550 K. The refractive indices increase linearly at a rate of 2 × 10$\text{}^{-5}$ K$\text{}^{-1}$ with increasing temperature.