Illumination system of a microlithographic projection exposure apparatus with a birefringent element

An illumination system, comprising:

• a mirror arrangement comprising a plurality of mirror units displaceable independently of each other to alter an angle distribution of light reflected by the mirror arrangement, each mirror unit comprising at least one mirror element;
• and
• at least one element that is in front of the mirror arrangement in a propagation direction of the light so that the at least one element is configured to produce at least two different states of polarization incident on different mirror units and/or different mirror elements,
• wherein:
• the at least one element comprises a birefringent element configured to split a partial ray of the light into an ordinary partial ray and an extraordinary partial ray;
• an entire portion of the partial ray contributes to the ordinary partial ray;
• the entire portion of the partial ray contributes to the extraordinary partial ray;
• the ordinary partial ray and the extraordinary partial ray have mutually perpendicular polarization directions;
• the ordinary partial ray is deflected by the mirror arrangement in a first direction;
• the extraordinary partial ray is deflected by the mirror arrangement in a second direction different from the first direction;
• and
• the illumination system is configured to be used in a microlithographic projection exposure apparatus.