X-Ray/EUV Multilayers: Promise And Pitfalls

Abstract

The enhanced reflectance achieved by recent developments in X-ray optics multilayer technology have 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 even at X-ray wavelengths. Preliminary results of actual flight data from such systems suggests great promise of scientific achievement from this new technology. It is widely recognized that supersmooth substrates are required since microroughness can seriously reduce the reflectance obtained from the multilayer. The (spectral) reflectance has thus become the most common measure of performance in the evaluation of X-ray multilayers. This ability to collect radiation and direct it toward a focal plane is a necessary but not sufficient condition for producing high quality images. The second and equally important condition is the ability to concentrate that radiation in a very small region in the focal plane. It is this condition that allows high spatial resolution images to be obtained. Conventional optical requirements are tolerable since these systems are usually far from diffraction-limited at their operational wavelengths. Optical substrates with satisfactory figure and for X-ray/EUV applications have been successfully demonstrated. However, image quality degradation due to spatial optical fabrication errors which bridge the gap between and finish is not nearly so well understood. It is the small angle scatter produced from these mid spatial frequency optical fabrication errors that will limit the practical resolution attainable from this promising new technology. Parametric optical performance predictions illustrating the capabilities and limitations of X-ray multilayers will be presented. The results of these calculations indicate that sub arc second resolution is indeed possible provided sufficiently smooth layer interfaces are maintained; however, image degradation occurs in a rather non-intuitive manner with varying interface PSD slope.© (1989) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.