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Proceedings Paper

Iridium optical constants for the Chandra X-ray Observatory from reflectance measurements of 0.05-12 keV
Author(s): Dale E. Graessle; Regina Soufli; Andy L. Aquila; Eric M. Gullikson; Richard L. Blake; Anthony J. Burek
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Paper Abstract

We present optical constants derived from synchrotron reflectance measurements of iridium-coated X-ray witness mirrors over 0.05-12 keV, relevant to the Chandra X-ray Observatory effective area calibration. In particular we present for the first time analysis of measurements taken at the Advanced Light Source Beamline 6.3.2 over 50-1000 eV, Chandra's lower-energy range. Refinements to the currently tabulated iridium optical constants (B. L. Henke et al., At. Data Nucl. Data Tables 54, 181-343, 1993 and on the Web at will become important as the low-energy calibration of Chandra's X-ray detectors and gratings are further improved, and as possible contaminants on the Chandra mirror assembly are considered in the refinement of the in-flight Ir absorption edge depths. The goal of this work has been to provide an improved tabulation of the Ir optical constants over the full range of Chandra using a self-consistent mirror model, including metallic layers, interface roughness, contaminating overlayer, and substrate. The low-energy data present us with a considerable challenge in the modeling of the overlayer composition, as the K-absorption features of C, O, and N are likely to be present in the ~10A overlayer. The haphazard contamination and chemical shifts may significantly affect optical constants attributed to this overlayer, which will distort the iridium optical constants derived. Furthermore, the witness mirror contamination may be considerably different from that deposited on the flight optics. The more complex modeling required to deal with low-energy effects must reduce to the simpler model applied at the higher energies, which has successfully derived optical constants for iridium in the higher energy range, including the iridium M-edges, already used in the Chandra calibration. We present our current results, and the state of our modeling and analysis, and our approach to a self-consistent tabulation.

Paper Details

Date Published: 3 February 2004
PDF: 13 pages
Proc. SPIE 5165, X-Ray and Gamma-Ray Instrumentation for Astronomy XIII, (3 February 2004); doi: 10.1117/12.506132
Show Author Affiliations
Dale E. Graessle, Smithsonian Astrophysical Observatory (United States)
Regina Soufli, Lawrence Livermore National Lab. (United States)
Andy L. Aquila, Lawrence Berkeley National Lab. (United States)
Eric M. Gullikson, Lawrence Berkeley National Lab. (United States)
Richard L. Blake, R&D Services (United States)
Anthony J. Burek, SFA Inc. (United States)

Published in SPIE Proceedings Vol. 5165:
X-Ray and Gamma-Ray Instrumentation for Astronomy XIII
Kathryn A. Flanagan; Oswald H. W. Siegmund, Editor(s)

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