Patent ID: 7710640

Claim:
A projection objective, comprising: at least one lens which as a consequence of intrinsic birefringence causes a maximum retardation of at least 25 nm/cm, wherein the projection objective has an optical compensation of a polarization such that a retardation which is caused by the projection objective is less than 0.25 times as large as the operating wavelength of the projection objective, and the projection objective is configured to be used in a microlithographic projection exposure apparatus, and wherein: the projection objective is configured to project an image of a mask that can be set in position in an object plane onto a light-sensitive coating layer that can be set in position in an image plane; the projection objective is configured to operate in an immersion mode, the projection objective is configured to produce at least one intermediate image and comprises an optical subsystem on the image-plane side which projects the intermediate image into the image plane with an image-plane-side projection ratio β i , wherein β i =NA IMI /NA IP , wherein NA IMI represents the numerical aperture at the location of the intermediate image and NA IP represents the numerical aperture on the image-plane side, the image-plane-side projection ratio β i has an absolute value of at least 0.3; and the projection objective is of a purely refractive design.