Coherent Fourier ellipsometry for characterization of thin films on transparent substrates

Non-contact quantitative characterization of nanostructures on transparent substrates is important for applications spanning flexible displays, photovoltaic devices, and advanced optical coatings. Conventional ellipsometric techniques, while widely used, often face limitations such as interference from backside reflection and insufficient spatial resolution for nanoscale mapping. In this study, we introduce coherent Fourier ellipsometry (CFE) as what we believe to be a novel approach enabling precise parameter estimation of thin films on transparent substrates with high spatial resolution. The core principle of CFE involves encoding multi-angle reflection coefficients for both s- and p-polarized light into spatially resolved reflected light field generated by a tightly focused beam. This rich optical information, extracted through quantitative analysis of phase and polarization diversity, facilitates inverse modeling and accurate determination of the sample's physical properties. We rigorously validated CFE's accuracy through comprehensive numerical simulation and experimental measurements of ITO films on transparent glasses. Owing to its high spatial resolution, non-invasiveness, and suitability for nanoscale probing, we believe CFE emerges as a powerful and versatile tool for thin film characterization on transparent substrates in optical and semiconductor industries.