Single and multi-channel Al-based multilayer systems for space applications in EUV range

Abstract

We report on further development of reflective mult ilayer coatings containing aluminum as low absorbin g material for the extreme ultra-violet (EUV) applications, in par ticular for solar physics. Optimizations of the mul tilayer design and deposition process have allowed us to produce Al-ba sed multilayers having relatively low interface rou ghness and record EUV reflectances in the range from 17 to 40 nm. The peak reflectance values of 56 % at 17.5 nm, 50 % a t around 21 nm, and 42 % at 32 nm were achieved with new three-material multilayers Al/Mo/SiC and Al/Mo/B 4C at near-normal incidence. We observe a good temporal stability of optical parameters of the multilayers over the peri od of 4 years. Moreover, the multilayer structure remains stable u pon annealing at 100 °C in air during several weeks . We will discuss the optical properties of more comp lex Al-based systems with regard to the design of m ultilayer coatings that reflect more than one wavelength and reject so me others within the spectral range from 17 to 40 n m. Such multichannel systems with enhanced reflectance and selec tivity would provide a further advance in optical p erformance and compactness of EUV solar imaging instruments. We will discuss general aspects of design, optimization and fabrication of single- and multi-channel multilayer mirrors mad e with the use of aluminum. We will present recent results on the EUV reflectivity of multilayer coatings based on th e Al/Mo/SiC and Al/Mo/B 4C material combinations. Al-based multilayer systems are proposed as optical coatings in EUV telescopes of future space missions and in other EUV applications.