A microinterferometric method for analysis of rotation-symmetric refractive-index gradients in intact objects

SUMMARY A new method for measuring refractive-index gradients in rotation-symmetric objects is described. Interference micrographs of intact objects, with the symmetry axis perpendicular to the optical axis of the microscope, are used to obtain a phase-shift profile, which is converted into a refractive-index profile by a computer program. The conversion calculations are based on iterative approximations of the gradient slope in a number of presumed shells in the object. The method is fast, convenient and yields highly accurate results even when only a small number of phase shift values can be obtained. The new method is especially advantageous for analysing many invertebrate eyes but it can also be used for measuring manufactured graded-index optical fibres.