Diffraction gratings metrology and ray‐tracing results for an XUV Raman spectrometer at FLASH. (6th December 2017)

• Record Type: Journal Article
• Authors: Dziarzhytski, Siarhei; Siewert, Frank; Sokolov, Andrey; Gwalt, Grzegorz; Seliger, Tino; Rübhausen, Michael; Weigelt, Holger; Brenner, Günter
• Is Part Of: Journal of synchrotron radiation. Volume 25:Part 1(2018)
• Page Start: 138
• Page End: 144
• Publication Date: 2017-12-06
• Subjects: X‐ray optics -- XUV Raman spectrometer -- metrology for synchrotron optics -- NOM -- reflectometry -- ray tracing; Synchrotron radiation -- Periodicals; Free electron lasers -- Periodicals; 539.73505
• DOI: 10.1107/S1600577517013066
• Languages: English
• ISSNs: 0909-0495

Abstract

Abstract : Investigations of the diffraction gratings for the high‐resolution XUV Raman spectrometer at FLASH via both ex situ and in situ metrology and ray tracing. Abstract : The extreme‐ultraviolet double‐stage imaging Raman spectrometer is a permanent experimental endstation at the plane‐grating monochromator beamline branch PG1 at FLASH at DESY in Hamburg, Germany. This unique instrument covers the photon energy range from 20 to 200 eV with high energy resolution of about 2 to 20 meV (design values) featuring an efficient elastic line suppression as well as effective stray light rejection. Such a design enables studies of low‐energy excitations like, for example, phonons in solids close to the vicinity of the elastic line. The Raman spectrometer effectively operates with four reflective off‐axial parabolic mirrors and two plane‐grating units. The optics quality and their precise alignment are crucial to guarantee best performance of the instrument. Here, results on a comprehensive investigation of the quality of the spectrometer diffraction gratings are presented. The gratings have been characterized by ex situ metrology at the BESSY‐II Optics Laboratory, employing slope measuring deflectometry and interferometry as well as atomic force microscopy studies. The efficiency of these key optical elements has been measured at the at‐wavelength metrology laboratory using the reflectometer at the BESSY‐II Optics beamline. Also, the metrology results are discussed with respect to the expected resolving power of the instrument by including them in ray‐tracing studies of the instrument.