Open AccessAlignment of the aberration‐free XUV Raman spectrometer at FLASH
Author(s) -
Biednov Mykola,
Brenner Günter,
Dicke Benjamin,
Weigelt Holger,
Keitel Barbara,
Rübhausen Michael,
Dziarzhytski Siarhei
Publication year - 2019
Publication title -
journal of synchrotron radiation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.172
H-Index - 99
ISSN - 1600-5775
DOI - 10.1107/s160057751801576x
Subject(s) - optics , monochromator , spectrometer , beamline , physics , extreme ultraviolet , laser , stray light , beam (structure) , wavelength
An extreme‐ultraviolet (XUV) double‐stage Raman spectrometer is permanently installed as an experimental end‐station at the PG1 beamline of the soft X‐ray/XUV free‐electron laser in Hamburg, FLASH. The monochromator stages are designed according to the Czerny–Turner optical scheme, adapted for the XUV photon energy range, with optical elements installed at grazing‐incidence angles. Such an optical scheme along with the usage of off‐axis parabolic mirrors for light collimation and focusing allows for aberration‐free spectral imaging on the optical axis. Combining the two monochromators in additive dispersion mode allows for reaching high resolution and superior stray light rejection, but puts high demands on the quality of the optical alignment. In order to align the instrument with the highest precision and to quantitatively characterize the instrument performance and thus the quality of the alignment, optical laser interferometry, Hartmann–Shack wavefront‐sensing measurements as well as off‐line soft X‐ray measurements and extensive optical simulations were conducted. In this paper the concept of the alignment scheme and the procedure of the internal optical alignment are presented. Furthermore, results on the imaging quality and resolution of the first monochromator stage are shown.