An Interferometric Measurement of Index of Refraction

Author: Shumate, Michael Stewart

Year: 1964

Degree: Engineer's thesis

Advisor: George, Nicholas A.

Committee Member: Unknown, Unknown

Option: Electrical Engineering

DOI: 10.7907/RYZC-8410

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.

Of the several common methods for measurement of the index of refraction of solid optical materials, only one, the minimum deviation method, can conveniently be used for materials whose refractive index exceeds 1.8. The minimum deviation method requires that a large prism of the optical material be constructed; this is not always possible or feasible for some crystalline optical materials that are of current interest. A method for measurement of index of refraction is presented which requires a thin flat plate of the optical material and is unlimited in the range of refractive index it can cover.

The method uses a two-beam interferometer to determine the optical path length through the flat plate by tipping away from normal incidence through a measured angle. It may be used in the visible portion of the spectrum directly, or extended to other spectral regions with the use of a suitable detector. The technique is shown to have an overall accuracy of [plus or minus] 2 x 10[superscript -4] in the refractive index. An error analysis is presented which shows that sample plates that have a small wedge angle may be used with only slight deterioration in the accuracy. The method is applied to the measurement of the principal indices of refraction of crystalline barium titanate at several wavelengths in the visible spectrum.

An analysis of methods for using an interferometer to determine gradients of refractive index as well as refractive index dispersion is also presented.

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