Patent ID: 7336416

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 first layer thickness d 1 ; an intermediate layer comprising a second material and having a second layer thickness d 2 ; and a second spectral purity enhancement layer comprising a third material and having a third layer thickness d 3 , the second spectral purity enhancement layer being arranged on the multi-layer stack top layer, wherein the first material is selected from 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, the third material is selected from 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, the second material comprises a material different from the first and third materials, and d 1 +d 2 +d 3 has a thickness between 2.5 and 40 nm, and wherein the first, second and third materials and the first, second and third layer thicknesses are configured to minimize absorption and/or destructive interference of radiation having a wavelength selected from a first wavelength range of 5-20 nm, and maximize absorption and/or destructive interference of radiation having a wavelength selected from a second wavelength range of 100-400 nm.