Imaging capabilities of normal-incidence X-ray telescopes.

The enhanced reflectance achieved by recent developments in X-ray multilayer technology has made normal-incidence X-ray/EUV telescopes feasible for many applications of interest. Conventional optical designs with obvious advantages over the somewhat cumbersome grazing incidence designs of Kirkpatrick, Baez, and Wolter can thus be utilized. Preliminary results of actual flight data suggest great promise of scientific achievement from this new technology. It is widely recognized that "supersmooth" substrates are required since microroughness can decimate the reflectance of the multilayer. The results of parametric optical performance predictions indicate that subarcsecond resolution is possible provided sufficiently smooth layer interfaces are maintained. However, optical fabrication tolerances imposed on the substrate may require advances over the current state of the art.