Non-periodic multilayer coatings for solar applications: advantages and future perspectives

Multilayer (ML) coatings are a crucial technology for the development of EUV and SXR solar instrumentation, as they represent the only viable option for the development of high-efficiency normal incidence mirrors in such spectral range. However, the current standard MLs are characterized by a very narrow spectral band which is incompatible with the science requirements expected in the next generation of solar instruments. Nevertheless, recent advancement in ML technology has made the development of non-periodic stacks repeatable and reliable, enabling the manufacturing of mirrors with either multi-band or broad-band high efficiency. In this work, after briefly reviewing the state-of-the-art ML coatings for the EUV/SXR range, we investigate the possibility of using non-periodic stacks for the development of multiband and broad-band normal-incidence mirrors to be used in the next-generation missions.