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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.
In the field of astronomical X-ray telescopes, different types of optics based on grazing incidence mirrors can be used. This contribution describes the special design of a lobster-eye optics in Schmidt's arrangement, which uses dual reflection to increase the collecting area. The individual mirrors of this wide-field telescope are made of at silicon wafers coated with reflecting iridium layers. This iridium coatings have some advantages compared to more common gold layers as is shown in corresponding simulations. The iridium coating process for the X-ray mirrors was developed within a cooperation of the Aschaffenburg University of Applied Sciences and the Czech Technical University in Prague. Different mirror parameters essential for a proper function of the X-ray optics, like the surface microroughness and the problematic of a good adhesion quality of the coatings were studied. After integration of the individual mirrors into the final lobster-eye optics and the corresponding space qualification testing it is planned to fly the telescope in a recently proposed NASA rocket experiment.
This paper focuses on a theoretical background that motivated
the experimental campaign of multiple layer coatings of X-ray mirrors, and
the first results of the testing of the prepared samples. Simulations of the use
of different overcoats were performed in order to improve the reflectivity of
thin iridium coatings designed for X-ray optics effective in the energy up to
10 keV. Samples based on these simulations were prepared and are being tested
for the properties that influence the X-ray optical performance, such as layer
homogeneity, density and surface micro-roughness. Further the topic of the
coating stress was addressed, as it is an issue in case of thin, lightweight X-ray
mirrors and affects the time stability of layers. The discussion and preliminary
results conclude our contribution.