Patent ID: 8320043

Claim:
An illumination optical apparatus comprising: a polarization-modulating optical element which is made of an optical material with optical activity, and which has a thickness profile that varies as a function of an azimuth angle at a constant radius; a movable optical element; and a divergence-increasing optical element, wherein the illumination optical apparatus is an illumination system for a microlithography projection system, configured so that during use in the microlithography projection system the illumination system directs light along a light path from a light source unit of the microlithography projection system to a mask, where the divergence-increasing optical element, moveable optical element, and polarization-modulating optical element are positioned in the light path between the light source unit and the mask, with the moveable optical element being positioned in the light path between the polarization-modulating optical element and the mask and the polarization-modulating optical element being oriented in the light path so that light incident on different areas of the polarization-modulating optical element traverse different thickness of the optical material, and wherein the optical material with optical activity has an optic axis oriented parallel to the light path and a plane of oscillation of an electrical field vector for linearly polarized light that travels through the optical material along the optic axis is rotated by an angle with a magnitude proportional to a distance traveled by the linearly polarized light inside the optical material with optical activity.