EUV ILLUMINATION SYSTEM WITH A SYSTEM FOR MEASURING FLUCTUATIONS OF THE LIGHT SOURCE

The invention relates to an EUV (extreme ultraviolet) illumination system with at least one EUV light source (3) ; with an aperture stop and sensor arrangement (1) for the measurement of intensity fluctuations and/or position changes of the EUV light source (3), in particular in the range of the effectively utilized wavelengths, or of one of the intermediate images of the EUV light source (3) , wherein the aperture stop and sensor arrangement (1) includes an aperture stop (2.1) and an EUV position sensor (2.3) ; wherein the aperture stop and sensor arrangement (1) is arranged in such a way that the aperture stop (2.1) allows a certain solid angle range of the radiation originating from the EUV light source (3) or from one of its intermediate images (7) to fall on the EUV position sensor.