Determination of the refractive-index profile of light-focusing rods: Accuracy of a method using interphako interference microscopy

Two analysis procedures to determine the refractive-index profile using Interphako interference microscopy are compared for accuracy: (I) expressing the. profile as a five-nomial equation (proposed previously by Ohtsuka and Shimizu); (II) considering ray bending due to the index gradient and using Abel inversion (proposed by ga et al.). Computer simulations indicate that the errors of both procedures are comparable except for index mismatching between the specimen periphery (n_p) and immersion oil (n₂) where Analysis (I) is more accurate than Analysis (II). The partial splitting method is more practicable than total splitting for a rodlike specimen. In addition, the improved partial splitting procedure facilitates reduction of error. The index profiles of the two selected light-focusing plastic rods (LFR) were calculated with these two procedures in various conditions. The correlation between resulting profiles and measuring conditions agreed with the simulations. It is concluded that Analysis (I) is preferable to Analysis (II) when n_p ≠ n₂ and that the improved partial splitting procedure is a practicable method for determining the index profile of a LFR.