Various embodiments set forth techniques for characterizing films on optically clear substrates using ellipsometry. In some embodiments, a spectroscopic ellipsometer is configured to generate a light beam that has a relatively small spot size and is substantially absorbed by an optically clear substrate, thereby reducing or eliminating reflections from an interface between the substrate and air. Optical simulations can be performed to determine values for various parameters associated with the ellipsometer that minimize the reflections from the interface between the substrate and air and maximize reflections from an interface between a film and the substrate. In addition, graded films that include multiple layers can be analyzed using models of multiple layers.