  The optical constants of ruthenium in the spectral range 8 nm to 23.75 nm
with their corresponding uncertainties are derived from the reflectance of a
sputtered ruthenium thin film in the Extreme Ultraviolet (EUV) spectral range
measured using monochromatized synchrotron radiation. This work emphasizes the
correlation between structure modelling and the reconstructed optical
parameters in a detailed inverse-problem optimization strategy. Complementary
X-ray Reflectivity (XRR) measurements are coupled with Markov chain Monte Carlo
(MCMC) based Bayesian inferences and quasi-model-independent methods to create
a model factoring the sample's oxidation, contamination, and surface roughness.
The sensitivity of the modelling scheme is tested and verified against
contamination and oxidation. A notable approach mitigating the high
dimensionality of the reconstruction problem is elaborated with the results of
this work compared to two previously published datasets. The presented dataset
is of high interest for the continuing development of Extreme Ultraviolet
Lithography (EUVL) and EUV astronomy optical systems.
