Patent ID: 8675178

Claim:
An apparatus, comprising: a light source configured to generate pulsed light; an illumination device; a projection objective having an object plane and an image plane; a polarization-influencing optical element comprising first, second, third and fourth polarizer elements offset by 90° relative to one another in a circumferential direction about an optical axis of the illumination device, and wherein the first and second polarizer elements lie opposite one another and are transmissive to light of a first polarization direction, and wherein the third and fourth polarizer elements are transmissive to light of a second polarization direction perpendicular to the first polarization direction; and a photoelastic modulator between the light source and the illumination device, wherein the illumination device is configured to illuminate the object plane of the projection objective during use, the projection objective is designed to project an image in the object plane of the projection objective to the image plane of the projection objective during use, and the apparatus is a microlithographic projection exposure apparatus; wherein the apparatus is configured so that during use of the apparatus: the pulsed light emitted from the light source is modified by the photoelastic modulator and the polarization-influencing optical element so that a spatial distribution and polarization direction of the light emerging from the polarization-influencing optical element varies in a pulse-resolved fashion; and an illumination setting provided by the illumination device to illuminate a mask in the object plane is switched between a first polarized illumination setting optimized for a structure of the mask extending along a first direction and a second polarized illumination setting optimized for a structure of the mask extending along a second direction perpendicular to the first direction.