Precise optical constant determination in the soft X-ray, EUV, and VUV spectral range

Optical constants of materials are essential for predicting and interpreting optical responses, which is crucial when designing new optical components. Although accurate databases of optical constants are available for some regions of the electromagnetic spectrum, for the vacuum ultraviolet (VUV), the extreme ultraviolet (EUV), and soft X-ray spectral ranges, the available optical data suffer inconsistencies, and their determination is particularly challenging. Here, we present a selected example of ruthenium (Ru) for the determination of optical constants from the VUV to the soft X-ray spectral range using reflectivity measurements performed with synchrotron radiation. The subtleties of reflectivity measurements are discussed for a large wavelength range, from 0.7 to 200 nanometers.