Optical system of a microlithographic projection exposure apparatus

A method for improving an imaging property of an optical system comprising the following steps:

• a) providing an optical system wherein the optical system is one of an illumination system and a projection objective;
• wherein the optical system is contained in a microlithographic projection exposure apparatus and comprises an optical element having a curved surface that is exposed to projection light during a projection;
• b) determining positional data of a plurality of points on the surface by directing a measuring beam sequentially onto the plurality of points on the surface by using a movable beam deviating component positioned outside of the projection light;
• c) determining deviations of the positional data from target data;
• and
• d) implementing corrective measures such that the imaging property of the optical system is improved.

An optical system for use in a microlithographic projection exposure apparatus having an illumination system and a projection objective, the optical system comprising:

• an optical element positioned in one of an illumination system and a projection objective of a microlithographic projection exposure apparatus, the optical element having a curved surface which is exposed to projection light during a projection;
• a measuring device which is positioned outside a beam path of the projection light and which comprises:
• a light source producing coherent measuring light,
• a first tiltable deviating mirror that selectively directs the measuring light to at least one point on the surface of the optical element,
• a second tiltable deviating mirror that is synchronized with the first tiltable mirror and directs the measuring light reflected from the at least one point on the surface towards an interferometer in which the measuring light reflected from the at least one point on the surface interferes with a reference beam that does not impinge on the surface of the optical element.