Application of automated polarimeter macroscope for investigation of optical inhomogeneity in oxide single crystals

Optical inhomogeneity is one of the most important parameters of oxide crystals widely used in optics and electronics. A computer-controlled imaging polarimeter has been applied for studying the optical inhomogeneities in several oxide crystals pulled by the Czochralski technique (Nd:YAG, Nd:SrLaGa3O7, LiNbO3) or by the vertical Bridgman method (CaF2, BaF2). Three maps of the investigated sample-birefringence, the principal azimuth and transmission, are acquired within several seconds in a single measurement step. A quasiradial stress-induced birefringence distribution was observed in wafers cut out from the crystals pulled in the <111> direction and in Z-pulled LiNbO3. The maximum residual birefringence was found at or very close to the perimeters of the wafers with the exception of YAGs where this maximum occurred close to the core region. The absolute value of birefringence in wafers cut out from the bottom parts of the crystals was typically larger than in adequate samples descending from the top parts. Such measurements enabled selection of the best crystal areas used then for production of electro- optic modulators (LiNbO3) and lasers (YAG, SLGO).