EUV light source for producing a useful output beam for a projection exposure apparatus

An EUV light source (2) serves to generate a useful output beam (3) of EUV illumination light for a projection exposure apparatus for projection lithography. The light source (2) generates an EUV generation device (2c) having an EUV raw output beam (30). The raw output beam (30) has a circular or elliptical polarization (31). A useful polarization adjusting means (32) of the light source (2) exerts a with respect to the polarization direction of linearly polarizing effect (34) on the raw output beam (30) to the polarization setting of the useful output beam (3). The useful polarization adjusting means (32) has at least one in the beam path of the raw output beam (30) arranged phase delay component (37). This produces a net phase shift between the two linearly polarized waves which are superimposed on the polarization of the raw output beam (30) which is smaller than half a wavelength λ of the useful output beam (3) of the EUV-illumination light. The result is an EUV light source with an improved one for tripping optimized lighting output beam.