Patent ID: 8068279

Claim:
An optical system, comprising: at least one first light-conductance-increasing element, comprising: a substrate; and a plurality of diffractively or refractively beam-deflecting structures extending in a common first preferred direction, wherein: the plurality of diffractively or refractively beam-deflecting structures are supported by the substrate; the substrate comprises a first optically uniaxial crystal material having an optical crystal axis that is substantially parallel or substantially perpendicular to the first preferred direction, the optical system is configured to be used in an illumination device of a microlithographic projection exposure apparatus; the beam-deflecting structures comprise a second optically uniaxial crystal material; and during use of the optical system, a polarization state of light that impinges on the at least one first light-conductance-increasing element and a polarization state of light that exits the at least one first light-conductance-increasing element are the same.