The Duc de Chaulnes image-displacement method for determining the refractive indices of solids and liquids has the distinct advantage of yielding the local values of the indices at any specified site on the specimen. This has special importance in the case of ferroelectric crystals in which the measurements are to be made within a region occupied by a given type of domain. Lawless et al. and Miller have suggested some refinements of the method that improve its accuracy to 0.2%. However, these are inadequate to determine the extraordinary-ray indices. This paper reports refinements that give better accuracy (∼0.05%) and that can be used even in the case of biaxial crystals of which large size (∼10 mm) prisms cannot be obtained.
© 1980 Optical Society of America
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