Performance of multilayer-coated figured optics for soft x-rays near the diffraction limit

The imaging performance of a spherical mirror was measured at 14nm. A Foucault knife-edge test was used to determine the focal spot size formed by a 400 mm radius mirror at a numerical aperture of 0.04. The image formed by the mirror is compared with a single-layer AuPd coating is compared with that formed when coated with a Mo/Si multilayer. By fitting the results with a diffraction model, it is possible to quantify the change in effective surface figure caused by the multilayer. It is concluded that a multilayer-coated mirror can perform at the diffraction limit under certain conditions.