The effect of high temperature heat treatment on the directional homogeneity of LiNbO3 crystal studied through transmission ellipsometry

Pure and doped lithium niobate (LiNbO
3
) crystals heat treated at temperatures up to 1000°C under reduced/oxidized atmospheres were studied through normal incidence transmission ellipsometry in which a laser with a wavelength of 632.8 nm was employed. The differences in refractive indices between two orthogonal directions were calculated. Results show that the birefringence varies depending on thermal history of the samples.