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Proceedings Paper

Using iridium films to compensate for piezo-electric materials processing stresses in adjustable x-ray optics
Author(s): A. Ames; R. Bruni; V. Cotroneo; R. Johnson-Wilke; T. Kester; P. Reid; S. Romaine; S. Tolier-McKinstry; R. H. T. Wilke
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Paper Abstract

Adjustable X-ray optics represent a potential enabling technology for simultaneously achieving large effective area and high angular resolution for future X-ray Astronomy missions. The adjustable optics employ a bimorph mirror composed of a thin (1.5 μm) film of piezoelectric material deposited on the back of a 0.4 mm thick conical mirror segment. The application of localized electric fields in the piezoelectric material, normal to the mirror surface, result in localized deformations in mirror shape. Thus, mirror fabrication and mounting induced figure errors can be corrected, without the need for a massive reaction structure. With this approach, though, film stresses in the piezoelectric layer, resulting from deposition, crystallization, and differences in coefficient of thermal expansion, can distort the mirror. The large relative thickness of the piezoelectric material compared to the glass means that even 100MPa stresses can result in significant distortions. We have examined compensating for the piezoelectric processing related distortions by the deposition of controlled stress chromium/iridium films on the front surface of the mirror. We describe our experiments with tuning the product of the chromium/iridium film stress and film thickness to balance that resulting from the piezoelectric layer. We also evaluated the repeatability of this deposition process, and the robustness of the iridium coating.

Paper Details

Date Published: 23 September 2015
PDF: 8 pages
Proc. SPIE 9603, Optics for EUV, X-Ray, and Gamma-Ray Astronomy VII, 96031I (23 September 2015); doi: 10.1117/12.2191404
Show Author Affiliations
A. Ames, Harvard-Smithsonian Ctr. for Astrophysics (United States)
R. Bruni, Harvard-Smithsonian Ctr. for Astrophysics (United States)
V. Cotroneo, Harvard-Smithsonian Ctr. for Astrophysics (United States)
R. Johnson-Wilke, Pennsylvania State Univ. (United States)
T. Kester, NASA Marshall Space Flight Ctr. (United States)
P. Reid, Harvard-Smithsonian Ctr. for Astrophysics (United States)
S. Romaine, Harvard-Smithsonian Ctr. for Astrophysics (United States)
S. Tolier-McKinstry, Pennsylvania State Univ. (United States)
R. H. T. Wilke, Pennsylvania State Univ. (United States)

Published in SPIE Proceedings Vol. 9603:
Optics for EUV, X-Ray, and Gamma-Ray Astronomy VII
Stephen L. O'Dell; Giovanni Pareschi, Editor(s)

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