Laser conoscopy of large-sized optical crystals

Abstract

Conoscopic interferometry provides a simple method of non-destructive control of the quality of a number of ferro-piezoelectric and optical crystals. Standard optical microscopes, including some commercial instruments, are easily adapted for implementation of conoscopic studies, though limited to small handy samples with a thickness of the order of 0.5 mm. In the present work we show that the usage of wide convergent or divergent conical laser beams in a simple benchtop configuration makes it possible to examine large-sized optical crystals by the method of conoscopy, including samples elongated along the optical axis direction. As distinct from traditional optical microscopy the conoscopic figures obtained with the aid of the laser installment may contain tens and hundreds of isochrome fringes thus increasing the informative capabilities of the method. Large-sized crystals of LiNbO3 (Ø57×95 mm), TeO2 prisms (44×41×14mm) were examined experimentally at different angles between the optical axis and normal to the crystal surface. The experimental studies of different optical anomalies are confirmed by calculations based on the theoretical analysis given in a previous work of the authors.