Abstract:We present a variable line-space grating spectrometer for soft x-rays that covers the photon energy range between 130 and 650 eV. The optical design is based on the HettrickUnderwood principle and tailored to synchrotron-based studies of radiation-sensitive biological samples. The spectrometer is able to record the entire spectral range in one shot, i.e. without any mechanical motion, at a resolving power of 1200 or better. Despite its slit-less design, such a resolving power can be achieved for a source spot as large as (30 × 3000) µm 2 , which is important for keeping beam damage effects in radiation-sensitive samples low. The high spectrometer efficiency allows recording comprehensive two-dimensional resonant inelastic soft x-ray scattering (RIXS) maps with good statistics within several minutes. This is exemplarily demonstrated for a RIXS map of highly oriented pyrolytic graphite, which was taken within 10 min.

Blazed gratings are of dedicated interest for the monochromatization of synchrotron radiation when a high photon flux is required, such as, for example, in resonant inelastic X-ray scattering experiments or when the use of laminar gratings is excluded due to too high flux densities and expected damage, for example at free-electron laser beamlines. Their availability became a bottleneck since the decommissioning of the grating manufacture facility at Carl Zeiss in Oberkochen.To resolve this situation a new technological laboratory was established at the Helmholtz Zentrum Berlin, including instrumentation from Carl Zeiss. Besides the upgraded ZEISS equipment, an advanced grating production line has been developed, including a new ultra-precise ruling machine, ion etching technology as well as laser interference lithography. While the old ZEISS ruling machine GTM-6 allows ruling for a grating length up to 170 mm, the new GTM-24 will have the capacity for 600 mm (24 inch) gratings with groove densities between 50 lines mm À1 and 1200 lines mm À1. A new ion etching machine with a scanning radiofrequency excited ion beam (HF) source allows gratings to be etched into substrates of up to 500 mm length. For a final at-wavelength characterization, a new reflectometer at a new Optics beamline at the BESSY-II storage ring is under operation. This paper reports on the status of the grating fabrication, the measured quality of fabricated items by ex situ and in situ metrology, and future development goals.

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We modify groove profile of various blazed gratings with groove densities as great as 3600 lines/mm by dip coating with hardenable liquids with the aim of reducing the blaze angle. The groove profiles resulting from coatings with different layer thickness are measured by atomic force microscopy. A highly reproducible blaze angle reduction to as high as a factor of 6 is achieved with mechanically ruled as well as ion-beam-etched holographic blazed gratings. Blaze angles, to as small as 0.7 deg, which are required for vacuum-UV and soft-x-ray applications but can hardly be formed with sufficient groove profile accuracy by direct ruling, are realized with this coating technique.

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We have measured the topography and near-normal incidence EUV efficiency of five flat multilayer-coated polymerovercoated blazed ion-etched holographic test gratings. Blaze angles were in the range 2.0-4.1º. All gratings had a surface roughness <3 Å rms (20-4000 Å). The best grating had a measured efficiency of 29.9% in the second order at 157.9 Å and a derived groove efficiency of 53.0%. At the shortest wavelength investigated (100.0 Å) another grating produced a measured efficiency in the first order of 12.9% and a derived groove efficiency of 33.6%. In third order another grating produced a measured efficiency at 137.8 Å of 13.4% and a derived groove efficiency of 21.8%. To the best of our knowledge these values exceed previous published results. Some issues remain that may be associated with modification of the groove profile by the multilayer coating.