Optical system, in particular of a microlithographic projection exposure apparatus

The invention relates to an optical system, in particular of a microlithographic projection exposure apparatus, with an optical system axis (OA) and a polarization-influencing optical arrangement. According to one aspect, the polarization-influencing optical arrangement comprises at least one polarization-influencing optical element, which has a monolithic design and linear birefringence, wherein the overall absolute value of the birefringence of all of the polarization-influencing optical elements deviates by at most ±15% from the value lambda/2, wherein lambda is the working wavelength of the optical system, wherein the direction of the fast axis of this birefringence varies in a plane perpendicular to the optical system axis (OA) in the at least one polarization-influencing optical element, and wherein the distribution of the fast axis of the birefringence of the polarization-influencing optical element is brought about by radiation-induced defects, which are situated in at least one optically unused region of the element.