Refraction and birefringence of beta-BaB2O4 crystals in the temperature range between 20 and 850 degrees C

Temperature dependences of refractive indices of beta-BaB2O4 crystals are s tudied at three wavelengths of a mercury emission spectrum in the temperatu re range from 20 to 850 degrees C. It is found that the dependence n(o,e) = f(t) is linear over the entire temperature range, except for the interval between 150 and 300 degrees C, where some deviation from linearity was obse rved. The temperature dependence of the birefringence Delta n(0,e) = f(t) o f beta-BaB2O4 crystals is measured, and coefficients Delta n(o,e)/Delta t a re found.