Single-movement fixed-exit channelcut x-ray monochromator based on profiled surfaces

A fixed-exit channelcut monochromator, which requires only a single rotational movement, has been developed. It is based on profiled reflecting surfaces machined into a Si monocrystal. Two geometries have been evaluated theoretically: one for the energy range from 5 to 30 keV and another for the energy range from 3 to 8 keV. The latter was designed to fulfil the requirements at an x-ray microscopy beamline, where the monochromator must not introduce any change in the phase space of the x-ray beam in order to limit aberrations when microfocusing the beam with a Fresnel zone plate. A monochromator with a very simple and compact mechanical design has been built with this crystal and successfully tested under ultrahigh vacuum. The measured energy resolution (<1 eV at 5 keV) and throughput are close to the theoretical figures, and the monochromator’s suitability for spectroscopic investigations has been demonstrated. The measured beam exit stability was 150 μm over a 3.5–8 keV range. The influence of the crystal geometry on its energy acceptance, phase space degradation, throughput, and acceptable heat load is discussed.