A computer-controlled polarimeter–macroscope has been developed to measure birefringence (phase retardation), the principal azimuths and transmission in large area (up to 6 in. diameter) wafers. It consists of two HR-type linear polarizers which can be rotated simultaneously by a stepper motor versus an immobile wafer. The transmission axes of the polarizers can be set at either 90° or 0° (polariscopic mode) or at 45° (polarimetric mode). The ability of observing samples’ images in the polariscopic mode can be useful for, e.g., quick detection of macroscopic defects. In the polarimetric mode the arrangement is capable of collecting input data through a video frame grabber (VFG)/TV camera detecting system and calculate three maps as stated above within a fraction of a minute. In usual circumstances, using a VFG with 256 grey levels enables determination of birefringence with an error not greater than approximately 5×10−7, whereas errors of azimuths and transmission are of a fraction of a degree and of a percent, respectively. In this part of the work a theory of the method and a detailed error analysis are presented.

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The name “conoscope” in Greek suggests that this tool should be used for observing interference patterns of birefringent crystals in the convergent beam of light. As such, the conoscope has been frequently used in laboratories for quick and usually qualitative estimation of optical inhomogeneity of crystals. In this paper we have described details of the computer-controlled imaging conoscope used for quantitative investigation of optical inhomogeneity in uniaxial crystals. To the best of our knowledge, this is the first conoscope used in an automated arrangement. Its working is based on equations derived for a plane–parallel uniaxial crystal plate cut out obliquely to the optical axis, which is next applied for two specific plate orientations practically investigated, i.e. for plates cut out perpendicularly and parallelly to this axis. It was found that these equations are more accurate than those published by other investigators. A practical investigation of a LiNbO3 crystal pulled by the Czochralski method from a congruent melt has been presented. Two birefringence inhomogeneity maps acquired for the 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 that the optical inhomogeneity could be detected with a relative error usually not exceeding a small fraction of a percent.

A new technique has been developed for investigation of optical dispersion of either natural or stress-induced birefringence. A spectropolarimeter containing a computer-controlled monochromator and two plane polarizers records polariscopic images of a sample via a TV-camera and a video frame grabber in two polarizer configurations: parallel and crossed. From this technique, one may calculate a map of a certain dispersion parameter over the entire sample area, and can plot it as a function of the wavelength for an arbitrary sample point. This technique has been found to be useful for investigation of optical inhomogeneities involved in crystals by gamma and proton irradiation, as well as by the native crystallographic imperfections.

in many optical applications of anisotropic ciystals birefringence dispersion (BD) is at least so important as birefringence spatial inhoinogeneity itself in this work a new technique of 2-D mapping of paratneten related to BD in plane-parallel wafers of optical materials is reported. A computer-controlled imaging spectro-poiariineter is used for recording the wafers' images for consecutively varying wavelengths. Examples of practical measurements carried out on undoped and Cu-doped LiNbO3 are presented.1 ThITRODUCTION DBD(AJ) RDBD(A1) Optical inhomogeneity (01) is defined as a refractive index (isotropic materials) or birefringence (anisotropic materials) change per unit length. However, in frequent cases birefringence is not a sole parameter of the material that should be considered. It seems that birefringence dispersion (BD) rather than birefringence itself is a key parameter in manufacture of e.g. retardation plates, 2nd harmonic generators, or polarizers [ 1]. It is a well known fact that BD depends on composition in mixed crystals of the LiNhO3-type structure [2]. It is therefore possible that BD can be also influenced by stoichiornetry and crystalline imperfections in homogeneous crystals, although this hyphothesis needs stronger experimental verification. It seems then that definition of the 01 effect in crystalline materials should be reconsidered, and that BD ought to play here an important role.In this work a method of BD testing on the entire area of plane-parallel plate of crystalline material is presented and illustrated by measurement of undoped and Cu-doped LiNbO3 wafers. A TV camera and video frame grabbing (VFG) techniques are used for collecting the input data from the whole surface of the investigated wafer, and hence BD inhomogeneity (BDI) maps can be obtained in short time. Since one can not map a physical phenomenon, i.e. a curve showing birefringence changes with wavelength, a set of parameters characterizing the BD effect, including their values for the extreme wavelengths used in experiment, an average value, etc. , has been proposed. This technique can be also used for calculating the piezooptic (photoelastic) coefficients' dispersion in isotropic materials, i.e. when birefringence is involved by residual stresses. SPIE Vol. 3729 • 0277-786X/991$1O.OO 2 PRINCIPLES OF TIlE METHOD Only a brief account of the method will be given here, since it has been described with full detailes elsewhere [3],including also its error analysis. Before one begins describing the method it should be precisely defined what exactly has to be measured. At first sight it might be expected that the BD phenomenon could be most correctly defined by differential birefringence dispersion, i.e.An(A.)-An(A.where n is birefringence, X is wavelength (an increasing subscript denotes longer wavelength). However, it will be shown later that relative differential birefringence dispersion, i.e.(2) yields less erroneous results in practical measurements, and this parameter will be further considered in this work. It should b...