Illumination system of a microlithographic projection exposure apparatus

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 can 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 the light into an ordinary and an extraordinary ray;
• the ordinary and the extraordinary ray have mutually perpendicular polarization directions;
• the ordinary ray and the extraordinary ray can be deflected in different directions by the mirror arrangement;
• and
• the illumination system is configured to be used in a microlithographic projection exposure apparatus.