%0 Journal Article
%A Yashchuk, Valeriy V.
%A Samoylova, Liubov
%A Kozhevnikov, Igor V.
%T Specification of X-ray Mirrors in Terms of System Performance: new Twist to an old Plot
%J Optical engineering
%V 54
%N 2
%@ 0091-3286
%C Bellingham, Wash.
%I SPIE
%M PUBDB-2015-01502
%P 025108
%D 2015
%Z OA
%X In the early 1990s, Church and Takacs pointed out that the specification of surface figure and finish of x-ray mirrors must be based on their performance in the beamline optical system. We demonstrate the limitations of specification, characterization, and performance evaluation based on conventional statistical approaches, including root-mean-square roughness and residual slope variation, evaluated over spatial frequency bandwidths that are system specific, and a more refined description of the surface morphology based on the power spectral density distribution. We show that these limitations are fatal, especially in the case of highly collimated coherent x-ray beams, like beams from x-ray free electron lasers (XFELs). The limitations arise due to the deterministic character of the surface profile data for a definite mirror, while the specific correlation properties of the surface are essential for the performance of the entire x-ray optical system. As a possible way to overcome the problem, we treat a method, suggested by Yashchuk and Yashchuk in 2012, based on an autoregressive moving average modeling of the slope measurements with a limited number of parameters. The effectiveness of the approach is demonstrated with an example specific to the x-ray optical systems under design at the European XFEL.
%F PUB:(DE-HGF)16
%9 Journal Article
%U <Go to ISI:>//WOS:000350481900026
%R 10.1117/1.OE.54.2.025108
%U https://bib-pubdb1.desy.de/record/208017