Design and fabrication of multilayer reflective filters for a Ritchey-Chretien Lyman-alpha telescope
We report the design and fabrication of multilayer reflective filters for the self-filtering cameras of a Ritchey-Chretien Lyman-alpha (Ly-alpha) telescope that uses reflecting multilayer mirrors, polarizers, and filters. The Ly-alpha telescope is designed to measure the linear polization of hydrogen Ly-alpha line (121.6 nm) emissions from the solar corona. A key element of the filter design includes the development of pi multilayers optimized to provide maximum reflectance at 121.6 nm for the respective cameras without significant angular variation from 0 to 15-deg incident angles. We applied self-filtering concepts to design Ly-alpha telescope filters that are composed of two reflective mirrors. The calculated value of the net throughput is 28.38% with a 4-nm bandwidth at a center wavelength of 121.6 nm. The measured value is 27.35% with a less than 6-nm bandwidth at incidence angle 10 deg.