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Optical Engineering • Open Access

Specification of x-ray mirrors in terms of system performance: new twist to an old plot

Paper Abstract

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.

Paper Details

Date Published: 9 February 2015
PDF: 13 pages
Opt. Eng. 54(2) 025108 doi: 10.1117/1.OE.54.2.025108
Published in: Optical Engineering Volume 54, Issue 2
Show Author Affiliations
Valeriy V. Yashchuk, Lawrence Berkeley National Lab. (United States)
Liubov V. Samoylova, European XFEL GmbH (Germany)
Igor V. Kozhevnikov, A.V. Shubnikov Institute of Crystallography (Russia)

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