EUV and SXR multilayer coatings in solar physics: from the current aspects to the future perspectives

Multilayer coatings (MLs) are widely employed for the development of EUV and SXR space-based instrumentation for solar plasma diagnostics since they are the only viable solution for the realization of high-efficiency normal incidence mirrors in this spectral range. Almost all the current missions adopt standard periodic MLs whose reflectance is usually characterized by a high but narrow spectral band. However, future challenges in solar plasma diagnostics require instrumentation with increasingly effective areas and capable of simultaneously observing multiple spectral lines. Fortunately, recent advancement in MLs technology has made the development of new solutions which improve the standard performance achieved so far. For Instance, the possibility to deposit non-periodic stacks with high repeatability and reliability enables the manufacturing of mirrors with either multi-band or broad-band high efficiency. In this work, a study of non-periodic multilayer coatings for the EUV/SXR range is presented, discussing some future perspectives for the next-generation missions.