Bruno Nelles

Mo/Si multilayer coated laminar phase and ruled blaze gratings for the soft X-ray region

Abstract MoSi multilayer coated laminar and blaze gratings with about 1200 L/mm have been manufactured for near normal incidence operation at soft x-ray wavelengths above the Si L-edge λ ≥ 12.4 nm. Higher diffraction efficiencies (up to 11% at λ = 13.6 nm), as opposed to simple amplitude gratings, are achieved for a soft x-ray laminar phase grating coated with 24 Mo/Si bilayers. Two mechanically ruled blaze gratings have been coated with Mo/Si multilayers. The maximum 1st order efficiency of 32% at λ = 13.8 nm has been achieved for one of them due to a refined groove forming technique and an optimum matching of the blaze angle (0.8°) and the bilayer thickness (10.5 nm).

ComIXS on BACH: a compact soft x‐ray spectrometer operating at Elettra

To accommodate increasing interest in soft x‐ray inelastic scattering, a new spectrometer has been designed, constructed and commissioned at Elettra. This instrument uses as the dispersive element one of two interchangeable Variable Line Spacing (VLS) spherical gratings. The energy scan is performed by a 7 cm linear translation of a back illuminated CCD which also collects the zero order light, facilitating alignment and calibration. The two gratings have the same radius of curvature while the groove densities and the groove density variations differ by a factor four. Thus the energies focused by the gratings at a particular position differ by a factor of four. The total length of the instrument is 60 cm, the energy range covered is roughly 25–1000 eV and the expected resolving power ranges from 1000 to 5000. The spectrometer is now operating on the beamline Bach. It takes advantage of the small size of the photon spot in the experimental chamber and of the possibility to control the polarization of the i...

Groove profile modification of blazed gratings by dip coating with hardenable liquids

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.

A plane grating with single-layer coating for the sub-nanometer wavelength range

A diffraction plane grating with single-layer coating able to reach photon energy up to 3 keV (possibly 4 keV) will be adopted at the TwinMic beamline at ELETTRA. The TwinMic beamline will exploit the unique capabilities of the novel twin X-ray microscope, which combines scanning and full-field imaging microscopes in a single multipurpose end-station. The needed moderate energy resolving power will be provided by a variable included angle plane grating monochromator working in a collimated light mode (also known as collimated SX700). This configuration allows freely selection of the incidence and diffraction angles at the grating, therefore permitting, for instance, to optimize its efficiency. This monochromator uses two mechanically ruled gratings to cover a very wide working energy range. The first grating goes from 150 eV to 1000 eV while the second goes from 600 eV to 4 keV. The two gratings were ruled using the CARL ZEISS Grating Ruling Engine GTM6, which is operated under interferometric control. The high-energy plane grating, with a line density of 600 lines/mm, has a triangular profile with a blaze angle of 0.4° and an apex angle of 178°. The grating profile is ruled on a silicon substrate and is covered with a 30 nm thick gold film. The small blaze angle permits one to work in blaze condition at very grazing incidence angles and therefore allows reaching high photon energies not accessible by means of conventional gratings.

Design, manufacturing and testing of gratings for synchrotron radiation

The grating is one of the most important components of a monochromator. Figure accuracy and microroughness of the substrate, accuracy of the groove pattern, shape and uniformity of the groove profiles, and the reflection coating are to be brought to the technological limits, if optimum performance is requested. Precise testing is as important as accurate manufacturing. Some new aspects for these topics are presented. # 2001 Published by Elsevier Science B.V. PACS: 07.85

Design and efficiency characterization of diffraction gratings for applications in synchrotron monochromators by electromagnetic methods and its comparison with measurement

For the design and characterization of synchrotron monochromators in the XUV region it is advantageous to know the performance of the mirrors and gratings as exact as possible within the wavelength range of operation to get performance results under realistic conditions. For that reason, monochromator gratings for dipole radiation as well as for undulator radiation at BESSY II are investigated in their wavelength range of operation by two different methods of electromagnetic grating theory. The IESMP, developed at BIFO, is a special boundary integral method, while the other, LUMNAB, developed by M. Nevière and available at BESSY, is based on the differential equation method. Both methods are compared with measurements on a plane grating in fixfocus condition for an energy range from 150 eV to 1000 eV. The observed differences between both methods and between the numerical results and measurement are discussed. For a grating monochromator in a variable included angle scheme efficiencies from the IESMP calculations for the first and higher orders are compared with scalar theory. Because of significant differences in the predictions of both methods this has to be verified by measurement.

Gratings with Blaze Angles Down to 0.1° for Photon Energies up to 10 keV

A new technique for the patterning of blazed gratings with extremely small blaze angles down to 0.1° is described. Mechanically ruled gratings are transferred from the gold ruling layer into the silicon substrate by reactive ionbeam etching. The primarily ruled blaze angle can be reduced by a factor of up to 28. The plane blaze facets are maintained during the etching process resulting in high blaze efficiency. The rms micro roughness on the blaze facets, that affects the efficiency as well as the diffuse straylight is reduced to below 0.2 nm by this technique. Groove profiles of such gratings with various groove densities and blaze angles measured by atomic force microscopy are presented. Calculated diffraction efficiency and resolving power and the impact of grating imperfections on the monochromator and spectrometer design are discussed [1] and [2]. Plane blazed gratings patterned by this technique were delivered to BESSY and to Sincrotrone Trieste. The results of efficiency measurements of these grati...

High-efficiency multilayer-coated polymer-overcoated blazed ion-etched holographic gratings for high-resolution EUV astronomical spectroscopy

We have measured the topography and near-normal incidence EUV efficiency of five flat multilayer-coated polymer-overcoated blazed ion-etched holographic test gratings. Blaze angles were in the range 2.0-4.1°. 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.

Mo/Si multilayer-coated ruled blazed gratings for the soft-x-ray region

Two Mo/Si multilayer-coated blazed gratings have been fabricated for operation at soft-x-ray wavelengths above the Si L edge, λ ≥ 12.4 nm, at (near) normal incidence. The sawtooth profile of the grating structure was mechanically ruled into a 200-nm Au film that was deposited onto a plane glass substrate. To smooth the rough Au surface and to prevent interdiffusion of the Au film with the upper Mo/Si multilayer, a carbon film was evaporated onto the Au grating surface of one of the gratings before the deposition of the multilayer coating. We matched the multilayer grating, working on blaze in the third diffraction order, in which an absolute diffraction efficiency of 3.4% at a wavelength of 14 nm was measured, whereas only 1.1% was achieved for a similar grating (without a carbon interlayer). These efficiencies are higher than those obtained for other ruled blazed gratings reported in the literature. As a result of the multilayer and grating periodicity, the wavelength of diffraction can be tuned bya rotation of the grating, which is important for application in a soft-x-ray monochromator.

The Optical Components of the NIRSPEC Wheel Mechanisms

The Near-Infrared Spectrograph (NIRSPEC) on board the James Webb Space Telescope can be reconfigured in space for astronomical observation in a range of NIR sub-bands as well as spectral resolutions. Reconfiguration of the NIRSpec instrument will be achieved using a Filter Wheel Mechanism (FWA) which carries 7 transmission filters and one reflective mirror and a Grating Wheel Mechanism (GWA) which carries six gratings and one prism. The dispersive components on the grating wheel (GWA) cooperate with the edge transmission filters mounted on the filter wheel (FWA) which block the higher dispersion orders of the gratings. The paper gives an overview on the design of all optical elements, their key requirements and the employed manufacturing approach. Test results from breadboard and component level qualification phase are also given.