Mandrels manufacturing processes for Ni electroformed X-ray optics: profile errors contribution to imaging degradation

摘要

It is well known that slope errors introduced by warped profiles in X-ray Wolter-I astronomical mirrors are important for the image quality at the focal plane. At this regard, a study aiming at developing reliable methods to predict the image quality on the basis of measured profiles of mandrels and mirror shells replicated by Ni electroforming has been performed. We are interested in determinating which of the different available methods could be trusted. The image quality is studied in terms of the Half Energy Width (HEW), a parameter in principle predictable from the metrological data. Two main approaches have been employed to calculate the HEW: i) ray-tracing, that follows the path of every generated photon from the source to the focus after the reflection onto a surface generated by the measured profiles; ii) the so called δ_(50) (delta 50) method, i.e. considering the slope errors distribution coming from the difference between Wolter profile and measured profile. The analysis is performed by means of software packages specifically written for this aim. They allowed us to consider 2D longitudinal profiles or a 3D grid composed of longitudinal and azimuthal profiles. Analysed profiles belong to mandrels and mirror-shells developed during the feasibility studies of the SIMBOLX and eRosita missions. The data were taken by means of profilometers during the several phases of their manufacturing. Monitoring the HEW evolution was investigated also in order to understand possible errors introduced during the replica and integration process, and to understand effects visible in focal spot and PSF's at the best focus or at different sections along the optical axis.