Hard x-ray Wolter-I telescope using broadband multilayer coatings on replica substrates: problems and solutions

We present an approach to obtaining a modular hard x-ray Wolter-I type telescope based on combining present replication technologies, for complete sub-arc minute cylindrical shells, with deposition of Ni/C broad-band hard x-ray multilayers. Based on a combination of literature review, stress measurement, modelling, and characterization of a number of replica and non-replica optics using AFM, interferometry and grazing incidence reflection, we conclude that (1) it should be possible to fabricate sputter targets small enough to coat the inside of approximately equals 10 cm diameter shells (2) in spite of the large Ni/C multilayer stresses, calculations show that the structural integrity of the complete shells limit the deformation to less than 1% of the surface and; (3) the quality of multilayers coated on replicas with gold surfaces, is not as good as those coated on standard substrates. The mediocre quality is found to correlate with a large degree of roughness on nanometer length scales, which is most likely a result of the previously well-documented polycrystallinity of gold films. The mediocre quality of the multilayers on replicas would lead to a 2-fold reduction in the effective area.