Wilhelm Egle

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.

Manufacturing of Wolter-I mirror segments with slumped glass

In our ongoing studies of high precision glass slumping we have successfully formed the first Wolter-I X-ray mirror segments with parabola and hyperbola in one piece. It could be demonstrated that the excellent surface roughness of the 0.55 mm thick display glass chosen is conserved during the slumping process. The influence of several parameters of the process, such as maximum temperature, heating and cooling rates etc. have to be measured and controlled with adequate metrology. Currently, we are optimizing the process to reduce the figure errors down to 1 micrometer what will be the starting point for further, final figure error corrections. We point out that metrology plays an important role in achieving a high precision optics, i.e. an angular resolution of a few arcsec. In this paper we report on the results of our studies and discuss them in the context of the requirements for future X-ray telescopes with large apertures.

Production of the first mirror shell for ESA's XMM telescope by application of a dedicated large area replication technique

A large number of mirror shells are required for the European Space Agencys XMM telescope three mirror modules, each of which consists of 58 thin walled highly nested Wolter I mirrors. The specified performance of the XMM mirror modules requires new design concepts and application of new technologies for the production of the lightweight mirror shells. Under an ESA contract, Carl Zeiss is leading a European industrial/scientific consortium to develop technologies that allow production of real size XMM mirror shells by a dedicated metal/epoxy resin replication technique. In late 1988 the first full size XMM mirror shell was successfully replicated, having the following characteristics: total length 600 mm, maximum shell diameter 400 mm, carrier material/thickness graphite-epoxy/0.8 mm, replication layers gold/epoxy, and total replicated mirror surface 7500 cm2. The development, preparation, and mirror shell replication are described, and the first results of the performance of the mirror shell after measurements and x-ray testing are presented.

Source collection optics for EUV lithography

Next generation lithography is likely to deploy extreme UV (EUV) light at 13.5 nm wavelength for key manufacturing processes. Currently, all promising EUV light source concepts require efficient light collection optics in order to deliver sufficeintly high light power for profitable chip production. With densely nested Wolter-Type 1 reflective optics we designed, and fabricated such optics. In this paper we report on the latest achievements in design, development and on our first at wavelength testing results of such collection optics.

Mirror system for the German x-ray satellite ABRIXAS: I. Flight mirror fabrication, integration, and testing

The tight ABRIXAS program schedule requires 250 mirror shells to be produced, checked and accepted within one year. This means that the fabrication processes have to be fully understood and kept completely under control. This applies mainly for the major production steps, like gold-coating of the mandrels, Nickel electroforming, mirror shells release from the mandrels and mirror shells testing and acceptance. We will report about the way how we tackled these technical and logistic challenges. Another important step for the optical performance of ABRIXAS Mirror Modules is the integration of the 27 mirror shells in the structural parts. This process requires high skill and good control means, like optical collimator, CCD camera and sophisticated analysis tools in order to achieve optimal-co-alignment of the 27 mirror shells axes and best confocality. This is guaranteed by dedicated test-facilities and sophisticated analyses software. We will report about the results obtained on integrated single mirrors shells as well as on the assembly of all 27 mirror shells.

EUV collectors: design, development, fabrication, and testing

EUV sources are designed to emit radiation around 13.5 nm wavelength into a solid angle of up to 2π sr. With a suitable Wolter type 1 grazing incidence optic such EUV photons can be collected with high efficiency and focussed onto a preferred target. Such Wolter type 1 collectors are characterized by densely nested concentric and confocal mirror shells with fixed distance from the source and the intermediate image. In this paper we will report on optical and mechanical design, development, fabrication and testing of nested Wolter type 1 collectors, capable of collecting and imaging EUV photons at 13.5 nm wavelength with high efficiency.

Development and production of lightweight CFRP carriers for the XMM telescope x-ray mirrors

The European Space Agencys high throughput X-ray Telescope XMM (X-ray Multi Mirror Mission) has three modules each consisting of 58 highly nested monolithic Wolter I mirrors. The mirrors have diameters in the range between 300 and 700 mm, an axial length of 600 mm and a focal length of 7.5 m. Due to the high packing density within the mirror module the mirror shells have to be sufficiently thin, and due to the high number of mirrors the shells have to be as light as possible. In order to meet these requirements Carl Zeiss and Dornier have developed the CFRP/EPOXY mirror shell technology under ESA contract. In this paper the development and production of carriers of various sizes will be reported. It will be shown that the CFRP laminate with the lay-up chosen by Dornier is a good substrate for the replication of x-ray mirror shells.

Optical demonstration model for the XMM telescope based on lightweight CFRP/EPOXY x-ray mirrors

The ESA High Throughput X-ray Spectroscopy Mission (XMM) is a telescope with three modules each consisting of 58 highly nested Wolter I mirrors with a focal length of 7.5 m. Envisaged resolution for an XMM module is 27 arcsec Half Energy Width at 8 keV x-ray energy. Due to the high packing density of the mirror shells within such a telescope, thin walled and light weight mirrors are required. In this paper the results of production, integration and performance tests of XMM CRFP/EPOXY mirror shells of all sizes (diameters from 300 mm to 700 mm; length equals 600 mm; wall thickness from 0.7 mm to 1.3 mm) for the XMM telescope will be reported.

Development of technologies for production of high quality grazing incidence x-ray mirrors on graphite epoxy substrates

The design concept of the mirrors for the European Space Agencys high throughput x-ray spectroscopy mission XMM is characterized by thin (1 mm) graphite epoxy shells as the mirror structure and a replication technique to produce the mirror surface. The mirror microroughness is specified to r 0.5 nm (rms); profile errors should not exceed 2.5 arcsec. An ESA research study has been performed by Carl Zeiss and subcontractors (Dornier GmbH, Max Planck Institut fur Extraterrestrische Physik/Garching, University of Leicester, X-ray Astronomical Group, Dept. of Physics) to clarify whether graphite epoxy mirror structures are able to meet the tight XMM mirror figuring and surface requirements and to determine what measures have to be taken to overcome the typical problems associated with composite materials used as mirror substrates, such as print-through of fibers and inner structure, short term/long term stability, and water absorption and outgassing. The starting conditions and progress during development are described. The present status of optical and x-ray performance of replicated flat graphite epoxy mirrors is reported, and aspects for further improvement of graphite epoxy mirrors is discussed.

Fabrication of segmented Wolter type-1 mandrels for the Constellation-X mirror development program

Constellation-X is NASA’s next major X-ray observatory, planned to be launched in 2012-2013. Each of the four identical satellites contains a large diameter (1.6 m) spectroscopic X-ray telescope (SXT). The mirror assembly consists of many densely nested Wolter type 1 mirrors with segment angles of 30 and 60 degrees. The mirror segments will be made of thin, accurately shaped glass substrates onto which the reflective mirror surface is replicated from high precision, super polished mandrels. In this paper we report about design, fabrication, metrology and analyses of the optical performance of three prototype mandrels to be used by NASA in the constellation-X mirror development program. The prototype mandrels are characterized by the following features: Material: Zerodur; overall length: 1100 mm; segment angles: > 30°; radius at paraboloid-hyperboloid intersection: 800 mm, 600 mm and 500 mm; focal length: 10 000 mm.