Design and fabrication of multilayer mirrors for He-II radiation

Design, fabrication, and reflectance evaluation of multilayer mirrors for He-II radiation are described. Based on the available complex refractive indices of materials at the wavelength of 30.4 nm, Mg, Al, Si, Cr, and C were selected as small absorption material to be paired. Mo/Si and Sc found in previous works were also included. In referring to optimum design for the highest reflectance, multilayers of Al/Mg, Au/Mg, C/Mg, Sc/Mg, C/Si, Al/C, and Mo/Si were fabricated by ion-beam sputtering. The highest reflectance of 27% was observed by a 15-period Mg/Sc mirror.