Colorimetry-based retardation measurement method with white-light interference

A colorimetry-based retardation measurement (CBRM) method is presented. The specimen, between crossed polarizers, is illuminated with a white-light source. The retardation that is due to the birefringence of the specimen produces a white-light interference color. The x, y chromaticity coordinates of the color produced are measured with a spectrophotometer. The resulting x, y values are compared with a retardation x, y database that we obtained by measuring the retardation with an accurate Senarmont compensator and the x, y chromaticity values along the length of a 0-4-order quartz wedge. The technique was validated by the measurement of a variety of retardation plates. The retardation accuracy (mean error) of the CBRM method is shown to be 3.6 nm. The resolution is +/-0.2 nm, and the measurement range is 5-2150 nm. The method substitutes for a polariscope and eliminates errors associated with quarter-wave plates. The CBRM method does not utilize any moving parts and thus is fast and can be automated.