Patent ID: 8049964

Claim:
Optical element transparent for radiation with a wavelength λ in the ultraviolet wavelength range below 250 nm, comprising: a substrate with a refractive index n s larger than 1.8, and an antireflection coating formed on at least part of the surface of the substrate between the substrate and an ambient medium with a refractive index n A , wherein the antireflection coating comprises a high or medium refractive index layer adjacent to the substrate, and having a high refractive index larger than 1.8 or a medium refractive index between 1.58 and 1.8, respectively, wherein further ones of the high or medium refractive index layers alternate with a low refractive index layer with a low refractive index smaller than 1.58, and wherein the optical thicknesses of all the high or medium refractive index layers and of the low refractive index layers are such that reflection of the radiation is minimized.