Illumination optical unit for euv microlithography

The invention relates to an illumination optical unit for EUV microlithography comprising a first optical element (1) having a plurality of first reflective facet elements (3) and a second optical element (5) having a plurality of second reflective facet elements (7). In this case, each first reflective facet element (3) from the plurality of the first reflective facet elements (3) is embodied in such a way that it has a respective maximum number of different positions which defines a set - associated with said first facet element - consisting of second reflective facet elements (7) in that the set consists of all second facet elements (7) onto which said first facet element (3) directs radiation in its different positions during the operation of the illumination optical unit. In this case, the plurality of second reflective facet element (7) forms a plurality of disjoint groups, wherein each of the groups and each of the sets contain at least two second facet elements (7), and there are no two second facet e