High-sensitivity IR to UV broadband ellipsometry and transmission characterization of high-purity glasses

Abstract

Glasses are widely used as transparent substrates in thin-film and optical applications, but also as window materials in devices and operando cells. Determining the dielectric properties of the glass over a wide spectral range is often the crucial first step for the subsequent quantitative spectroscopic analysis, design and application of layer stacks and complex sample systems. Reflection-based ellipsometry—the method of choice for this task—is challenging for thick transparent substrates because of backside reflections that influence the optical response. Here, we extend the methodological treatment of backside reflections in ellipsometry by accounting for the spatial overlap—and its dependence on incidence angle, thickness and refractive index—between the light beams’ cross-sections and the detector aperture. We thereby demonstrate the incorporation of backside reflections in high-sensitivity multi-instrument, multi-angle ellipsometry and transmission for both measurement and quantitative modeling of glasses. Consolidating data from three instruments, we determine the dielectric function of two high-purity fused silica (Suprasil1) and quartz (Herasil102) glasses from the deep-ultraviolet to the mid-infrared (200–25000nm), with a sensitivity to absorption features as small as 10–7. Our non-destructive approach obviates the need for sample modifications like backside roughening, thus laying the foundation for future detailed ellipsometry studies on lower-purity glasses such as soda–lime- and borosilicate-based substrates for thin-film applications.