Reflecting properties of narrowband Si/Al/Sc multilayer mirrors at 58.4 nm.

This study considers the reflective characteristics of three-component Si/Al/Sc multilayer mirrors with a protective cap layer as candidates for telescopes for observation of the solar corona in the He I (=58.4) spectral line. At 58.4 nm, a peak reflectance of 32% and a spectral width at a half-maximum intensity of =5.4 are obtained. The temporal stability of the reflectance at =58.4 for Si/Al/Sc samples with a 6 nm thick cap layer is investigated during storage in air for 20 months.