Metal multilayer mirrors for EUV/ultrasoft X-ray wide-field telescopes.

Metal multilayer mirrors have been designed for the ALEXIS satellite, which is to carry six wide-field telescopes to perform an all-sky survey in three narrow EUV/ultrasoft X-ray wavelength bands. Low reflectivity at 304 Å is achieved by superposing two layer pairs that provide destructive interference with an effective 2d spacing of 152 Å. Calculations predict the 186 Å design will have a peak reflectivity at 186 Å of 35% and a 304 Å reflectivity less than 10^-5. In the laboratory the 304 Å reflectivity on a multilayer sample with a wavetrap has been measured to be as low as 10^-4. The authors present details of the calculations and laboratory measurements of the reflectivity performance obtained with prototype mirrors.