X-RAY-IMAGING AT THE DIFFRACTION LIMIT

We tested the ability of normal-incidence, multilayer-coated x-ray optics to produce diffraction-limited images. The imaging performance at 14 nm of a spherical mirror substrate coated with a single metal layer was compared with that of the same substrate coated with a Mo-Si multilayer. A knife-edge test was used to quantify the image aberrations. The knife-edge data were fitted with a model based on Fresnel diffraction theory. We found that the multilayer coating introduced a measurable but small figure error into the optic; the change in figure was less than lambda/16 peak to valley. We conclude that a properly deposited multilayer coating will not degrade the imaging performance of an optical system designed to operate at the diffraction limit.