Optical system, in particular for a microlithographic projection exposure apparatus

Optical system, comprising:

• (i) at least one first mirror which has an optically effective surface and, for electromagnetic radiation of a predefined operating wavelength impinging on the optically effective surface at an angle of incidence of at least 65° relative to a respective surface normal, has a reflectivity of at least 0.5, wherein the first mirror comprises:
• a reflection layer, and
• a compensation layer arranged above the reflection layer in a direction of the optically effective surface, the compensation layer having varying thickness;
• and
• (ii) at least one second mirror which, for the electromagnetic radiation of the predetermined operating wavelength impinging on the optically effective surface at an angle of incidence of at least 65° relative to the respective surface normal, has a reflectivity of at least 0.5,
• wherein, for a local variation of a reflectivity resulting from the first mirror and from the second mirror, which are arranged in succession in an optical beam path such that the first mirror directs the electromagnetic radiation of the predetermined operating wavelength onto an object plane of a projection lens, the at least one compensation layer, for an intensity distribution generated in a pupil plane or a field plane of the optical system during operation thereof, reduces a difference between the maximum and the minimum intensity value by at least 20% compared to an analogous system without the compensation layer.