Convenient interferometric method for refractive index determination

A Mach-Zehnder interferometer is used for the determination of refractive indices by measuring the change in optical path length through a sample as it is rotated about a vertical axis. The apparatus works equally well with low index as well as high index transparent optical materials. Interference orders are counted electronically. The refractive index of routinely processed samples that are moderately wedge shaped with non-flat surfaces can be measured to better than 1% accuracy.