An alternative method for measuring the index profile of a gradient-index lens

Abstract

An alternative method for measuring the index profile of the GRIN lens is proposed based on Fresnel's equations and the common-path phase-shifting interfermetry. A light beam composing of the right- nd the left- ircularly polarized components is obliquely incident on the tested GRIN lens and the reflected light passes through an analyzer. The light is collected and imaged by an imaging lens to a CMOS camera. Four interferograms under different additional phases are taken and Carre's phase-shifting method is used to calculate the full-field phase distribution. Next, the estimated data are substituted into the special equations derived from the Fresnel's equations, and the index profile of the GRIN lens can be obtained. Its validity has been demonstrated. It has both merits of the common-path interferemetry and the phase-shifting interferemetry.