UV spectral filtering by surface structures multilayer mirrors

A surface structured extreme ultraviolet multilayer mirror was developed showing full band suppression of UV (𝜆=100–400  nm) and simultaneously a high reflectance of EUV light (𝜆=13.5  nm). The surface structure consists of Si pyramids, which are substantially transparent for EUV but reflective for UV light. The reflected UV is filtered out by blazed diffraction, interference, and absorption. A first demonstration pyramid structure was fabricated on a multilayer by using a straightforward deposition technique. It shows an average suppression of 14 times over the whole UV range and an EUV reflectance of 56.2% at 13.5 nm. This robust scheme can be used as a spectral purity solution for all XUV sources that emit longer wavelength radiation as well.