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Proceedings Paper

Development of grazing incidence multilayer mirrors for hard x-ray focusing telescopes
Author(s): Peter H. Mao; Fiona A. Harrison; Yuriy Ya. Platonov; David M. Broadway; Brian DeGroot; Finn Erland Christensen; William W. Craig; Charles J. Hailey
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Paper Abstract

We are developing depth-graded, multilayer-coated mirrors for astrophysical hard x-ray focusing telescopes. In this paper, we discuss the primary technical challenges associated with the multilayer coatings, and report on progress to date. We have sputtered constant d-spacing and depth-graded W/Si multilayers onto 0.3 - 0.5 mm thick DURAN glass (AF45 and D263) and 0.4 mm thick epoxy replicated aluminum foils (ERAFs), both of which are potential mirror substrates. We have characterized the interfacial roughness, uniformity, and stress of the coatings. The average interfacial roughness of each multilayer was measured from specular reflectivity scans ((theta) i equals (theta) r) using Cu Kalpha x-rays. The thin film stress was calculated from the change in curvature induced by the coating on flat glass substrates. Thickness and roughness uniformity were measured by taking specular reflectivity scans of a multilayer deposited on the inside surface of a quarter cylinder section. We found that interfacial roughness ((sigma) ) in the multilayers was typically between 3.5 and 4.0 angstrom on DESAG glass, and between 4.5 and 5.0 angstrom on the ERAFs. Also, we found that coatings deposited on glass that has been thermally formed into a cylindrical shape performed as well as flat glass. The film stress, calculated from Stoney's equation, for a 200 layer graded multilayer was approximately 200 MPa. Our uniformity measurements show that with no baffles to alter the deposition profile on a curved optic, the layer thickness differs by approximately 20% between the center and the edge of the optic. Interfacial roughness, however, remained constant, around 3.6 angstrom, throughout the curved piece, even as the layer spacing dropped off.

Paper Details

Date Published: 15 October 1997
PDF: 9 pages
Proc. SPIE 3114, EUV, X-Ray, and Gamma-Ray Instrumentation for Astronomy VIII, (15 October 1997); doi: 10.1117/12.283791
Show Author Affiliations
Peter H. Mao, California Institute of Technology (United States)
Fiona A. Harrison, California Institute of Technology (United States)
Yuriy Ya. Platonov, Osmic, Inc. (United States)
David M. Broadway, Osmic, Inc. (United States)
Brian DeGroot, Osmic, Inc. (United States)
Finn Erland Christensen, Danish Space Research Institute (Denmark)
William W. Craig, Columbia Astrophysics Lab. (United States)
Charles J. Hailey, Columbia Astrophysics Lab. (United States)

Published in SPIE Proceedings Vol. 3114:
EUV, X-Ray, and Gamma-Ray Instrumentation for Astronomy VIII
Oswald H. W. Siegmund; Mark A. Gummin, Editor(s)

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