EN
A simple theoretical approach based on Kramers-Krönig relations predicts well the dispersion and birefringence of BaLaGa_{3}O_{7} and SrLaGa_{3}O_{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_{3}O_{7} and SrLaGa_{3}O_{7} is stable with respect to the temperature region of 300-550 K. The refractive indices increase linearly at a rate of 2 × 10^{-5} K^{-1} with increasing temperature.