Optical heterogeneity of a fused quartz disk

In preparing a refractive index standard of fused quartz, having the form of a 60°prism, it was considered advisable to investigate carefully the optical density of this glass since appreciable variations might be present because of nonuniform heat treatment or other factors.With this in view the standard, together with nine small auxiliary prisms, was cut from a disk 52 mm in diameter and 13 mm thick.The indices of these prisms were measured, for five different wave lengths, to an accuracy of a few units in the sixth decimal place.As a result, the standard is adjudged uniform within the limits of ±4X 10 -6 in its index of refraction.The optical heterogeneity distribution found within the whole disk is in accord with the hypothesis that the variations are caused mainly by temperature gradients which exist during the annealing or which change during the cooling procedures. CONTENTSPage I. Relative variations in certain properties of fused and crystalline quartz.619 II.Requirements for prismatic standards of refractive index 622 III.Preparation of an index standard and the auxiliary prisms 623 IV.The index data and their interpretation 624 I.