Abstract
For photon energies of 1 - 5 keV, blazed gratings with multilayer coating are ideally suited for the suppression of stray and higher orders light in grating monochromators. We developed and characterized a blazed 2000 lines/mm grating coated with a 20 period Cr/C- multilayer. The multilayer d-spacing of 7.3 nm has been adapted to the line distance of 500 nm and the blaze angle of 0.84° in order to provide highest efficiency in the photon energy range between 1.5 keV and 3 keV. Efficiency of the multilayer grating as well as the reflectance of a witness multilayer which were coated simultaneously have been measured. An efficiency of 35% was measured at 2 keV while a maximum efficiency of 55% was achieved at 4 keV. In addition, a strong suppression of higher orders was observed which makes blazed multilayer gratings a favorable dispersing element also for the low X-ray energy range.
Highlights
Crystals and gratings are used in monochromators at synchrotron radiation sources since about five decades to filter out wavelengths for experiments in the hard and soft x-ray photon energy range
Very interesting is the strong suppression of higher orders which for grating monochromators working at lower photon energies might be a very attractive feature
The material choice Cr/C turned out to be optimal for the tender x-ray range
Summary
Crystals and gratings are used in monochromators at synchrotron radiation sources since about five decades to filter out wavelengths for experiments in the hard and soft x-ray photon energy range. It was about 30 years ago that the gap between grating and crystal monochromators has been closed at 2 keV, the performance of both types of monochromators is still problematic in this range. 1 keV, grating monochromators require very shallow grazing angles of incidence in order to keep a high reflectivity This means the gratings have a small acceptance and they are working close to the total external reflection angle, which pulls off intensity from +/− 1st and other diffraction orders. The amount of stray light increases above 1.5 keV when the angular spacing between first and zero order becomes very small
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