Imaging ellipsometry for curved surfaces

The authors propose a new design of an imaging return-path ellipsometer, which enables reflection-based measurements of both flat and curved surfaces. Return-path ellipsometry (RPE) based on mirrors cannot be applied to surface characterization of a specimen with a free-form shape. The authors circumvent this restriction by using microsphere-based retroreflectors instead of a mirror. The measurement equation for retro reflection-based RPE is very similar to that for mirror-based RPE. Therefore, the authors first outline the difference between conventional (unidirectional) and return-path (bidirectional) ellipsometry by focusing on Mueller-matrix ellipsometry. Furthermore, they present a new ellipsometer consisting of a rotating reflector to determine the surface inclination for almost arbitrary media when scattering and diffraction are negligible.