Klaus Heidemann

Optics and mechanisms for the Extreme-Ultraviolet Imaging Spectrometer on the Solar-B satellite.

The Extreme-Ultraviolet Imaging Spectrometer (EIS) is the first of a new generation of normal-incidence, two-optical-element spectroscopic instruments developed for space solar extreme-ultraviolet astronomy. The instrument is currently mounted on the Solar-B satellite for a planned launch in late 2006. The instrument observes in two spectral bands, 170-210 A and 250-290 A. The spectrograph geometry and grating prescription were optimized to obtain excellent imaging while still maintaining readily achievable physical and fabrication tolerances. A refined technique using low ruling density surrogate gratings and optical metrology was developed to align the instrument with visible light. Slit rasters of the solar surface are obtained by mechanically tilting the mirror. A slit exchange mechanism allows selection among four slits at the telescope focal plane. Each slit is precisely located at the focal plane. The spectrograph imaging performance was optically characterized in the laboratory. The resolution was measured using the Mg iii and Ne iii lines in the range of 171-200 A. The He ii line at 256 A and Ne iii lines were used in the range of 251-284 A. The measurements demonstrate an equivalent resolution of ~2 arc sec? on the solar surface, in good agreement with the predicted performance. We describe the EIS optics, mechanisms, and measured performance.

Electron-beam-deposited Mo/Si and MoxSiy/Si multilayer x-ray mirrors and gratings

For the wavelength region above the Si- L edge normal incidence, soft x-ray mirrors are produced with peak reflectivities close to 60%. The multilayer systems consist of molybdenum and silicon and are fabricated by electron beam evaporation in ultrahigh vacuum. A smoothing of the boundaries, and thereby a drastic enhancement of the reflectivity, is obtained by thermal treatment of the multilayer systems during growth. The thermal stability of the multilayer stacks could be improved considerably up to 850° C by mixing Mo and Si in the absorber layers and producing thus Mo x Si y /Si multilayers with x and y denoting the amounts of Mo and Si in the absorber layer, respectively. First attempts are reported to produce mirrors with a bilayer thickness of 2.6 nm. An improvement in the quality of these interfaces can be obtained by bombardment with Ar + ions. We report on normal incidence reflectivity measurements of the mirrors with synchrotron radiation and finally on the normal incidence diffraction efficiencies of a Mo/Si multilayer coated grating, for which values of 5.5% are achieved for the + 1st and - 1st diffraction orders.

Efficiency of a multilayer-coated, ion-etched laminar holographic grating in the 14.5–16.0-nm wavelength region

The efficiency of an ion-etched laminar holographic grating was measured at near-normal incidence in the 14.5-16.0-nm wavelength range. The grating had an electron-beam-evaporated Mo/Si multilayer coating matched to the grating groove depth. The efficiency peaked at 16.3% in the first inside order at 15.12 nm and 15.0% in the first outside order at 14.94 nm. These are believed to be the highest efficiencies obtained to date from a multilayer-coated laminar grating at near-normal incidence in the EUV (lambda<30.0nm) . Zero and even orders were almost completely suppressed. The grating groove efficiency in the first order approached the theoretical limit of 40.5%.

EUV spectral purity filter: optical and mechanical design, grating fabrication, and testing

The radiation emitted from an EUV source is collected and focused by a suitable collector system. A reflective blazed grating is used in -1st diffraction order to select a definite spectral band around 13.5 nm wavelength from the broad-band emission spectrum of the source. The effective grating area is segmented into a set of different plane gratings, mounted on a common base plate. In order to focus the light from the collector system, the grating segments are tilted and form a best-fit polygon surface. A specific groove density variation on the grating segments significantly improves the imaging performance. In this paper, we report on design, fabrication and testing of the grating system.

Record high extreme-ultraviolet efficiency at near-normal incidence from a multilayer-coated polymer-overcoated blazed ion-etched holographic grating.

We have measured the extreme-ultraviolet (EUV) efficiency of a polymer-overcoated blazed ion-etched holographic test grating. The grating had a magnetron-sputtered Mo2C/Si multilayer coating matched to the grating blaze angle of 2.78 degrees. At an angle of incidence of 5.6 degrees and a wavelength of 15.79 nm, the measured efficiency peaks in the second outside order at 29.9%. The derived groove efficiency is 53.0%. To the best of our knowledge these are the highest values obtained yet at EUV wavelengths from a holographic ion-etched blazed grating.

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.

Proposed multilayer-grating designs for the Astrophysical Plasmadynamic Explorer (APEX): an EUV high-resolution spectroscopic SMEX

APEX is a proposed mission for a Small Explorer (SMEX) satellite. The instrument is a suite of 8 near-normal incidence EUV spectrometers and is the outgrowth of 17 years of research at NRL on multilayer coatings and holographic ion-etched diffraction gratings. A prototype spectrometer has been flown successfully on a sounding rocket. We have examined different multilayer and gratings designs and produced a configuration optimized for the proposed science. APEX will achieve a peak effective area of at least 30-50 cm2 in the range 90-275 Å with resolution ~10,000, significant improvements on Chandra and EUVE.

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

The joint astrophysical plasmadynamic experiment (J-PEX) high-resolution EUV spectrometer: diffraction grating efficiency

We have fabricated five new holographic ion-etched polymer-coated gratings for a reflight on a sounding rocket of the J-PEX high-resolution EUV spectrometer. The gratings are parabolic (nominal 2000-mm focal length), large (160 mm x 90 mm), and have a blazed groove profile of high density (3600 grooves/mm at the vertex). They have been coated with a high-reflectance multilayer of Mo/Si/C. Using an atomic force microscope, we examined grating topography before multilayer coating. The surface roughness is 2 angstrom rms and the blaze angle is near the target value of 2.4°. Using synchrotron radiation, we completed an efficiency calibration map of each multilayer-coated grating over the wavelength range 220-245 angstrom. At an angle of incidence of 5°, the average efficiency in the first inside order peaks near 234 angstrom. The average peak efficiency is 12.3 ± 1.0% for Grating 1, 12.6 ± 2.4% for Grating 2, 12.6 ± 1.8% for Grating 3, 14.1 ± 3.0% for Grating 4, and 13.0 ± 1.0% for Grating 5. The derived groove efficiency averaged over all gratings is approximately 50%, which meets our goals. Refined models of the multilayer gratings are required to resolve remaining issues.