US Patent 7701554 Lithographic apparatus, device manufacturing method, and optical component

An optical component for use in a lithographic apparatus. The optical component includes an optical element having an optical surface for reflecting electromagnetic radiation, and a protective zone covering the optical surface. The protective zone is provided with a material that substantially protects the optical surface against sputtering when the optical component is in use. The material has a refractive index that approximately equals unity for at least a predetermined wavelength of electromagnetic radiation to which the optical surface is exposed.