Subsystem of an illumination system of a microlithographic projection exposure apparatus

In general, in one aspect, the disclosure features an illumination system for a microlithographic projection exposure apparatus configured so that during operation the illumination system illuminates a reticle plane of the microlithographic projection exposure apparatus with light of a desired polarization distribution. The illumination system includes a first polarization-influencing optical element and a second polarization-influencing optical element. During operation the first polarization-influencing optical element converts a first polarization distribution produced by a light source unit into a second polarization distribution which is different from the first polarization distribution. The second polarization-influencing optical element converts the second polarization distribution into a third polarization distribution corresponding to the desired polarization distribution, the second polarization-influencing optical element causing an effective rotation of the preferred polarization direction through 90° over its optically effective surface.