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Previously used mirror technologies are not suitable for the challenging needs of future X-ray telescopes. This is why the required high precision mirror manufacturing triggers new technical developments around the world. Some aspects of X-ray mirrors production are studied within the interdisciplinary project INTRAAST, a German acronym for "industry transfer of astronomical mirror technologies". The project is embedded in a cooperation of Aschaffenburg University of Applied Sciences and the Max-Planck-Institute for extraterrestrial Physics. One important task is the development of low-stress Iridium coatings for X-ray mirrors based on slumped thin glass substrates. The surface figure of the glass substrates is measured before and after the coating process by optical methods. Correlating the surface shape deformation to the parameters of coating deposition, here especially to the Argon sputtering pressure, allows for an optimization of the process. The sputtering parameters also have an influence on the coating layer density and on the micro-roughness of the coatings, influencing their X-ray reflection properties. Unfortunately the optimum coating process parameters seem to be contrarious: low Argon pressure resulted in better micro-roughness and higher density, whereas higher pressure leads to lower coating stress. Therefore additional measures like intermediate coating layers and temperature treatment will be considered for further optimization. The technical approach for the low-stress Iridium coating development, the experimental equipment, and the obtained first experimental results are presented within this paper.
To predict the angular resolution of future X-ray telescopes combined from thermally formed thin glass mirror segments, submicron accuracy is required on the shape measurements of the individual mirror substrates. A dedicated cross-calibration campaign using instruments of different European research institutions is presented.
In the field of X-ray astronomy different types of telescope optics based on grazing incidence mirrors can be used. This contribution presents a special design of a Lobster Eye wide-field telescope with mirrors based on flat silicon wafers and the task of coating such mirror substrates with reflective iridium layers.
An der Hochschule Aschaffenburg werden iridiumbasierte Schichtsysteme für röntgenastronomische Anwendungen hergestellt. Unter Nutzung eines Weißlichtinterferometers wurde hierfür ein Verfahren zur Vermessung der inhärenten Schichtspannungen entwickelt. Erste vielversprechende Ergebnisse von spannungsarmen Röntgenreflexionsbeschichtungen werden vorgestellt.
Future investigations of astronomical X-ray sources require light weight telescope systems with large collecting areas and good angular resolution. The Wolter I type telescope design offers a suitable possibility for obtaining performant X-ray mirrors with high collecting areas. The technology based on replicated slumped glass optics using thin glasses thereby provides the opportunity to fulfil the light weight and mass production requirements. In NASA's telescope NuSTAR this technology has been proven as advantageous compared to previous systems. Coating thin glasses with iridium, gold or platinum enhances the reflectivity of X-ray mirrors.
High angular resolution, large collecting area and reduced weight per unit area are required for astronomical X-ray telescopes of the next generation observatories. New technologies for processing X-ray mirrors are under development to fulfill these needs. One option is to realize a Wolter I type telescope constituted of several hundred nested thin and light-weight X-ray mirror segments. The individual mirror segments need to be coated with an about 100 nm thick film of a high-reflective material to enhance the reflectivity for X-rays. Thereby an accurate shape metrology of the segments is necessary to predict the angular resolution of the astronomical telescope as well as to control the development process of X-ray mirrors. We present the challenges in shape measurements of thin glasses used to control the coating process and first experimental results about the repeatability of the measurements.
Das Projekt JEUMICO wird vom Projektträger BAYHOST im Rahmen eines
Programms für bilaterale wissenschaftliche Projekte zwischen Tschechien und
Bayern gefördert. Inhaltlich werden von der Hochschule Aschaffenburg und der
Technischen Universität Prag hier gemeinsam Röntgenoptiken für ein geplantes
astronomisches Experiment an Bord einer NASA-Höhenrakete entwickelt.
Future space-based X-ray observatories need to be very lightweight for launcher mass constraints. Therefore they will
use a reduced mirror thickness, which results in the additional requirement of low coating stress to avoid deformation of
the initial precisely shaped mirror substrates. Due to their excellent reflection properties iridium coatings are sometimes
applied for grazing incidence mirrors in astronomical X-ray telescopes. At Aschaffenburg University of Applied
Sciences the coating of thin iridium films by an RF-magnetron sputtering technique is under development. The work is
embedded in collaborations with the Max-Planck-Institute for Extraterrestrial Physics in Germany, the Czech Technical
University in Prague, the Osservatorio Astronomico di Brera in Italy, the German Leibniz Institute for Solid State and
Materials Research in Dresden, and the French Institute Fresnel. Sputtering with different parameters leads to iridium
films with different properties. The current work is focused on the microstructure of the iridium coatings to study the
influence of the substrate and of the argon gas pressure on the thin film growing process. Correlations between coating
density, surface micro-roughness, the crystalline structure of the iridium layers, and the expected reflectivity of the X-ray
mirror as well as coating stress effects are presented and discussed. The final goal of the project is to integrate the
produced prototype mirrors into an X-ray telescope module. On a longer timescale measurements of the mirror modules
optical performance are planned at the X-ray test facility PANTER.
Indirect glass slumping of grazing incidence mirror segments for lightweight x-ray telescopes
(2017)
The paper provides a description of recent progress in the development of lightweight, precision and highthroughput
grazing-incidence mirrors for X-ray astronomy made of glass. In particular, the indirect slumping
technology under investigation at the Max Planck Institute for Extraterrestrial Physics (MPE) is reviewed and
recent activities are presented together with the research approach. The glass slumping technique foresees
several steps: a thermal forming process using a suitable mould; a re
ective layer application; the alignment
and integration of mirror segments into a supporting structure; and the nal verication of prototype modules
using X-rays. Each step is considered at MPE, with the involvement of partner institutes and universities. The
last year of activities was mainly dedicated to the procurement of new moulds and to the application of Iridium
coating. The main results will be presented.
X-ray astronomy uses space-based telescopes to overcome the disturbing absorption of the Earth´s atmosphere. The telescope mirrors are operating at grazing incidence angles and are coated with thin metal films of high-Z materials to get sufficient reflectivity for the high-energy radiation to be observed. In addition the optical payload needs to be light-weighted for launcher mass constrains. Within the project JEUMICO, an acronym for “Joint European Mirror Competence”, the Aschaffenburg University of Applied Sciences and the Czech Technical University in Prague started a collaboration to develop mirrors for X-ray telescopes. The X-ray telescopes currently developed within this Bavarian- Czech project are of Lobster eye type optical design. Corresponding mirror segments use substrates of flat silicon wafers which are coated with thin iridium films, as this material is promising high reflectivity in the X-ray range of interest. The deposition of the iridium films is based on a magnetron sputtering process. Sputtering with different parameters, especially by variation of the argon gas pressure, leads to iridium films with different properties. In addition to investigations of the uncoated mirror substrates the achieved surface roughness has been studied. Occasional delamination of the iridium films due to high stress levels is prevented by chromium sublayers. Thereby the sputtering parameters are optimized in the context of the expected reflectivity of the coated X-ray mirrors. In near future measurements of the assembled mirror modules optical performances are planned at an X-ray test facility.