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Optical constants

Optical Constants in the EUV and Soft X-ray Spectral Range

Scattering and absorption of photons are the basis of many scientific, industrial and medical applications. For the metrological reconstruction of nanostructures or the optimization of functional surfaces, knowledge of the optical constants and their fundamental parameters is of crucial importance. Every simulation of the photon-matter interaction is based on the optical constants. Especially in the soft X-ray range, however, significant differences to already known literature data sets can occur. The reasons for this are manifold. Some of them are extrapolated values calculated from atomic scattering factors. Often differences between the optical constants of thin nm layers compared to bulk like materials can be observed. Oxidations or other impurities that occur in production processes can be further causes for deviating optical constants. Measuring the absorption, i.e. the loss of photons passing through a medium, is one of the easiest ways to measure the optical constants directly. Especially in the EUV range this approach is mostly not practical due to the strong absorption and the extremely thin samples required. The measurement of the EUV reflection and the subsequent modeling in a forward calculation is a possible alternative to determine the optical constants.

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