Retroreflex ellipsometry for isotropic substrates with nonplanar surfaces

Ellipsometry is a widely-used and highly-accurate method for characterizing materials and thin films, though conventional ellipsometry restricts the geometric shape of samples to flat or nearly flat surfaces. For nonplanar surfaces, the beam path of the reflected or transmitted light will be altered owing to the curvature of the surfaces. The concept of retroreflex ellipsometry was developed at Fraunhofer IOSB to overcome the limitation of conventional ellipsometry via a retroreflector (retroreflective sheet). However, prior information regarding the samples is still necessary. In this paper, retroreflex ellipsometry is combined with reflectance measurements to derive the optical properties for isotropic substrates with nonplanar surfaces using the reflectance R and the ellipsometric data (PS, D) without prior knowledge of incident angles. The experimental results show that this retroreflex ellipsometry prototype has excellent accuracy and precision for the full Mueller matrix measurement and is capable of measuring refractive indices of nonplanar surfaces.