Surface Shape Measurement for Small Lens Using Phase Shift Shearing Interferometer

Abstract

In discussing small-lens surface shape measurement, a shearing interferometer with a plane-parallel glass plate is used to shape a laterally sheared beam from an induced test beam, producing interferogramreflecting wavefront phase distribution. This approach is robust against disturbance thanks to common-path interferometry and to the single solid glass plate. The Degree Of Freedom (DOF) for the shape of targets is high because no reference surfaces are needed. These make our proposal practical for use in the actual factory environment. The phase shift we use to analyze the interference fringe is induced by tilting a shear plate in this configuration, which is far cheaper than conventional equipment using PZT actuators. Our interferometer’s phase distribution shows a differential image of the target wavefront, so detected phase distribution must be integrated to get the original surface shape, as confirmed in the sections that follow.