On the optical constants of cobalt in the M-absorption edge region

Abstract

Using monochromatized synchrotron radiation, the optical constants of cobalt are determined in the spectral range 8.0–25.0 nm. The optical constants are determined from Angle-Dependent Reflectometry (ADR) measurements of a multilayer sample. Since cobalt is prone to strong oxidation, carbon capping was used to stabilize the probed sample. The fine-structure of the optical constants in the M-absorption edge region is resolved with unprecedented resolution for the element. The determination of the optical constants from reflectivity data was conducted using Markov Chain Monte Carlo (MCMC) based Bayesian inferences, supported with X-ray Reflectivity (XRR) data. This work further demonstrates establishing MCMC-based Bayesian inferences for determining optical constants. Time-Frequency Analysis (TFA) methods are also used to solve the corresponding inverse problem by supporting initializing a model of the sample. The results here are highly relevant for developing Co-based Multilayer Mirrors (MLMs) targeting the Extreme Ultraviolet (EUV) range, particularly those MLMs dedicated for EUV astronomy.