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.
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.
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.