Measuring Refractive Index Inhomogeneity Using Deflectometry

Abstract

Precisely knowing the refractive index of a piece of glass can be a complicated and expensive task and knowing it over a large area gets even more difficult. We are proposing a method that can measure the inhomogeneity of the refractive index of an optic while utilizing a large area and is cost effective.. We are proposing the use of multiple deflectometry measurements that will calculate the difference between two surface maps where the only change is the introduction of small variations to the refractive index under test. This system is based on the geometry of fringe reflection deflectometry to measure the slope of an object rapidly and accurately. By placing a fluid on top of the usual mirror used in a deflectometry system, we can measure the slope of a mirror that is equivalent to this “liquid lens”. Then introduce a piece of glass with a refractive index similar to the fluid and measure again. Subtracting the two images allows for the calculation of the difference in the refractive index thus allowing us to see the inhomogeneity across the glass in question.