Interferometric measurement of the refractive-index distribution in plastic lenses by use of computed tomography

A nondestructive measurement method that makes possible the measurement of a three-dimensional refractive-index distribution of any shape plastic lens is presented. In this method, a Mach-Zehnder interferometer and shearing interferometer are combined into a single optical system and are used selectively. Interference fringes of a test object that is immersed in matching liquid are detected at various rotation angles. And transmitted wave fronts are calculated with these interference fringes. Finally, the refractive-index distribution is obtained by computed tomography analysis. In addition, accurate control of the matching liquid temperature makes it possible to measure the absolute refractive index of the test object. This system has good performance with a measurement accuracy of 10(-4) or better peak to valley.