Axel Matthes

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.

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.

Measuring large aspherics using a commercially available 3D-coordinate measuring machine

A CNC-controlled precision measuring machine is a very powerful tool in the optical shop not only to determine the surface figure, but also to qualify the radius of curvature and conic constant of aspherics. We used a commercially available 3D-coordinate measuring machine (CMM, ZEISS UPMC 850 CARAT S-ACC) to measure the shape of the GEMINI 1-m convex secondary mirrors at different lapping and polishing stages. To determine the measuring accuracy we compared the mechanical measurements with the results achieved by means of an interferometrical test setup. The data obtained in an early stage of polishing were evaluated in Zernike polynomials which show a very good agreement. The deviation concerning long wave rotational symmetrical errors was 20 nm rms, whereas the accuracy measuring of mid spatial frequency deviations was limited to about 100 nm rms.

Recent results on manufacturing of segmented x-ray mirrors with slumped glass

Future X-ray missions are aiming at large mirror collecting areas of the order of several square meters. This is obtained with mirror assemblies composed of a large number of segments. The angular resolution of each one must be measured separately down to 1 arcsec. The mass limits imposed by the launchers require low weight and high stiffness materials. In this context we have focused our recent studies on the manufacturing of thin glass mirror segments. These mirrors are made from sheet glass which can be shaped in a high-precision slumping process to e.g. a Wolter-I figure. The excellent surface roughness of the sheet glass chosen is conserved during the slumping process and the final figure corrections with non-contacting tools. The influence of several parameters of the process, such as glass and mould material, heating and cooling, has been measured and controlled with adequate metrology. In this paper we describe our current efforts which are aiming at the production of a Wolter-I scaled demonstration model - preferentially with parabola and hyperbola in one piece - made of thin sheet glass.

Figuring, polishing, metrology, and performance-analyses of Wolter type 1 forming mandrels for the Constellation-X mirror development program

Constellation-X, NASAs next major X-ray observatory, is planned to be launched in 2012/2013. Each of the four identical spacecraft contains a large diameter, spectroscopic X-ray telescope (SXT). The mirror assembly is compsed of many densely nested Wolter type 1 mirror reflectors, having segment angles of 30 or 60 degrees. The reflectors will be made of thin, accurately shaped glass sheets, onto which the reflective mirror surface is replicated from high precision, super polished Zerodur mandrels. One key issue for high-performance mirrors is the exact shape of the glass substrates. They are produced at NASA/GSFC by a dedicated hot forming process (slumping) from precision forming mandrels. The hot forming process requires special materials for the glass substrates and the forming mandrels. In this paper we report on figuring (precision machining), polishing, metrology and performance analyses of Wolter type 1 forming mandrels. The mandrels are characterized by the following features: Mandrel dimensions: 450 x 640 mm2; radius of curvature: ~800 mm; segment angle: ~40 deg; shape: hyperboloid or paraboloid; material: Zerodur K20 (Keatite) or fused silica (quartz).

Fabrication of a demonstration mandrel for ESA's XEUS mirror development program

ESAs XEUS x-ray telescope design asks for segmented Wolter 1 mirror plates with radii up to 5 m and a focal length of 50 m. The mirror plates shall have an excellent optical performance (< 5 arcsec HEW). They shall be made by metal (e.g. Nickel) electroforming. This design approach requires highest quality segmented Wolter 1 mandrel plates, with an on-axis HEW < 2 arcsec and a micro-roughness better than 0.3 nm (rms). We will report about the novel design concept, fabrication approach and verification of the x-ray optical performance of the first XEUS demonstration mandrel.