OPTICAL SYSTEM

摘要

An optical system comprising an optical element arranged on an optical axis in the path of a radiation beam. The optical element (2; 116; 202) comprises a birefringent material and has a non-planar face (4) through which the radiation beam passes. The optical system comprises a polarisation control system for controlling polarisation of the radiation beam such that the radiation beam has a polarisation which is non-uniform across a cross section (21; 24) taken perpendicular to the optical axis, the non-uniform polarisation having a distribution corresponding with a shape of the said non-planar face.