Project exposure system for microlithography

Projection exposure system of micro lithographs a) with an optical element; b) with a projection light source which emits radiation, wherein the surface coverage of the optical element with the radiation of the projection light source is not rotationally symmetric; c) and a compensating light supply means for supplying compensation light to the optical element such that the temperature distribution in the optical element, which is carried out by cumulative application of heat of the optical element with light projecting and compensating, at least partially homogenized, characterized in that the compensation light supply means (11, 14 to 19; 111; 211; 311, 314-319) a light source (17; 317) and at least one optical fiber (11; 111; 211; 311) comprises, in the from the light source (17; 317) emitted radiation (16; 316) to the optical element (1; 101; 201; 301) is fed through the peripheral surface thereof.