Patent ID: 7463413

Claim:
A multi-layer mirror, comprising a multi-layer stack, the multi-layer stack comprising a plurality of alternating layers with a multi-layer stack top layer and a spectral filter top layer arranged on the multi-layer stack, the spectral filter top layer comprising a first spectral purity enhancement layer comprising a first material and having a layer thickness d 1 and being arranged on the multi-layer stack top layer, wherein the first material is selected from SiN, Si 3 N 4 , SiO 2 , ZnS, Te, diamond, CsI, Se, SiC, amorphous carbon, MgF 2 , CaF 2 , TiO 2 , Ge, PbF 2 , ZrO 2 , BaTiO 3 , LiF or NaF, wherein the first material and the layer thickness d 1 are selected to enlarge the ratio of radiation having a wavelength selected from a first wavelength range of 5-20 nm and radiation having a wavelength selected from a second wavelength range of 100-400 nm in a beam of radiation of a source emitting radiation with a wavelength in each wavelength range.