The phase difference between s and p polarization of the light reflected from a material is used for measuring the material's complex refractive index. First, two phase differences that correspond to two different incidence angles are measured by heterodyne interferometry. Then these two phase differences are substituted into Fresnel's equations, and a set of simultaneous equations is obtained. Finally, the equations are solved by use of a personal computer by a numerical analysis technique, and the complex refractive index of the material can be estimated.

A new method for measuring the refractive index is presented. First, the phase difference between s and p polarizations that is due to the total internal reflection is measured by heterodyne interferometry. Then, substituting this phase difference into the Fresnel equations, we can obtain the refractive index of the test medium.

Based on the effect that the phase difference between s-and p-polarizations at the total-internal-reflection is changed with the variation of the air refractive index, which is related to the air pressure, a new optical method for measuring the air pressure of a vacuum cavity is proposed. From the experimental curve of the phase difference variation measured by the heterodyne interferometry and the calibrated pressure measurement of a vacuum cavity, an empirical formula is derived. With this empirical formula, the measurable range of this new optical method is 760 to 0.1 torr.

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In a new type of liquid refractometer, the phase difference variation between s and p polarizations produced by the total internal reflection is measured using a heterodyne interferometer with a specially designed probe. Substituting the phase difference variation into the Fresnel's equation, the refractive index can be calculated and displayed. The prototype is set up to demonstrate its feasibility.