Optical characterization of surfaces by robust reflectance determination based on air-gap interference

In this work we present an optical tool for characterizing the reflectance and polarimetric properties of surfaces. It uses only the image of the interference fringe pattern produced in a thin air-gap between the surface of interest and a glass surface acting as a reference. From only the contrast of the fringe pattern captured with a CCD we may obtain the reflectance of the surface, no need of measuring a reference beam. By taking two images with polarized light, we may get then the polarized reflectance Rp and Rs, but also the ellipsometric magnitude D, simply as a phase shift between fringes in p and s polarization. A sample of silicon with a thin layer of thermally grown silica is used to test the method.