Measuring the atomic scattering factors near the iridium L-edges for the Athena silicon pore optics reflector

Abstract

Athena, a future high-energy mission, is expected to consist of a large aperture x-ray mirror with a focal length of 12 m. The mirror surface is to be coated with iridium and a low Z overcoat. To define the effective area of the x-ray telescope, the atomic scattering factors of iridium with an energy resolution less than that (2.5 eV) of the x-ray integral field unit are needed. We measured the reflectance of the silicon pore optics mirror plate coated with iridium in the energy range of 9 to 15 keV and that near the iridium L-edges in steps of 10 and 1.5 eV, respectively, at the synchrotron beamline SPring-8. The L3, L2, and L1 edges were clearly detected around 11,215, 12,824, and 13,428 eV, respectively. The measured scattering factors were ∼3% smaller than the corresponding values reported by Henke et al., likely due to the presence of an overlayer on the iridium coating, and were consistent with those measured by Graessle et al. The angular dependence of the reflectivity measured indicates that the iridium surface was extremely smooth, with a surface roughness of 0.3 nm. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Fine structure of the atomic scattering factors near the iridium L-edges

“…The similarity to Clancy12 can also be seen in the best-fit parameters of L3. Comparing the best-fit parameters obtained by Awaki et al 9 with previous works, 1,20 the best-fit parameters (center energy and line width) of L3 WL were consistent with previous works 1,20 (see Table 1). Clancy12 also measured L 2 WL and estimated the branching ratio to be 3.2, which is larger than that of our result.…”

“…The dash-dotted lines indicate the energies (11215.7 AE0:3 eV, 12824.3 AE0:9 eV, and 13426.5 AE0:6 eV) of L 3 , L 2 , and L 1 edges, respectively. 9 The gray line in the panels of L 2 and L 3 shows μðE Þ (arb. unit) obtained by Clancy12.…”

“…10,11 Although fine energy scans for measuring f 1 and f 2 near the edges are possible, estimating f 2 from μ can reduce the time required for ground calibration tests. 7,9 In Sec. 2, we introduce our x-ray measurements and calculate the atomic scattering factors from the reflectance.…”

“…This is demonstrated by measurements on the ground for building the response function of the x-ray mirror (e.g., ASTRO-H 7 and Chandra 8 ). We measured the reflectance of a sample fabricated by employing ESAs silicon pore optics (SPO) technology in the high energy region from 9000 to 15,000 eV at the synchrotron radiation facility SPring-8 9 and obtained the atomic scattering factors of iridium near L-edges with an energy pitch of 1.5 eV. We compare the f2 fine structure with XAFS and show that the method using reflection is as effective as XAFS methods.…”

“…In addition, it is becoming increasingly important to measure the fine structure of the atomic scattering factors because of the improvement in energy resolution of focal plane detectors in recent years 10 , 11 . Although fine energy scans for measuring f1 and f2 near the edges are possible, estimating f2 from μ can reduce the time required for ground calibration tests 7 , 9 …”