Patent ID: 7180667
Filing Date: 2007-02-20
Classification: G02B,G03F,Y10S

Abstract:
1. An objective comprising a plurality of lenses, wherein at least two lenses consist of fluoride crystal material with a cubic lattice structure and wherein said fluoride crystal lenses are (111)-lenses each having a lens axis oriented approximately perpendicular to the {111}-planes or to crystallographic planes that are equivalent to the {111}-planes of the fluoride crystal, wherein an image point in an image plane is formed at a convergence of a bundle of light rays each of which has an azimuth angle α R , an aperture angle θ R and an optical path difference ΔOPL for two mutually orthogonal states of linear polarization, wherein said (111)-lenses are arranged with a rotation relative to each other about the lens axes in such a manner that a distribution ΔOPL(α R , θ R ) of the optical path differences as a function of the azimuth angle α R and the aperture angle θ R has significantly reduced values of ΔOPL in comparison to an arrangement where said (111)-lenses are not arranged with said rotation relative to each other.