Precise measurement of thermal-induced refractive-index change in BaTiO₃ on the basis of anisotropic self-diffraction

We propose a method for precise measurement of the temperature-dependent refractive-index change in BaTiO₃ by use of anisotropic self-diffraction (ASD). In this method the refractive-index change corresponds to the angle deviation of the diffraction pattern. Because only the geometry of the ASD is used for measuring, the precision of measurement is independent of crystal thickness and environmental perturbation. The accuracy of the refractive-index change achieved is 10^-4 when the resolution of the measurement of the angle is ∼0.04°. Both the theory and the experiment are demonstrated.