IMAGING CONOSCOPE FOR INVESTIGATION OF OPTICAL INHOMOGENEITY IN LARGEBOULES OF UNIAXIAL CRYSTALS

The name ''conoscope'' in Greek suggests that this tool should be used for observing interference patterns of birefringent crystals in the c onvergent beam of light. As such, the conoscope has been frequently us ed in laboratories for quick and usually qualitative estimation of opt ical inhomogeneity of crystals. In this paper we have described detail s of the computer-controlled imaging conoscope used for quantitative i nvestigation of optical inhomogeneity in uniaxial crystals. To the bes t of our knowledge, this is the first conoscope used in an automated a rrangement. Its working is based on equations derived for a plane-para llel uniaxial crystal plate cut out obliquely to the optical axis, whi ch is next applied for two specific plate orientations practically inv estigated, i.e. for plates cut out perpendicularly and parallelly to t his axis. It was found that these equations are more accurate than tho se published by other investigators. A practical investigation of a Li NbO3 crystal pulled by the Czochralski method from a congruent melt ha s been presented. Two birefringence inhomogeneity maps acquired for th e above-mentioned two specific orientations in this crystal were used for eliminating its inhomogeneous areas from further use in optics. A theoretical error analysis carried out also in this work has shown tha t the optical inhomogeneity could be detected with a relative error us ually not exceeding a small fraction of a percent. (C) 1998 American I nstitute of Physics.