Abstract: An objective, in particular a projection objective for a microlithography projection-exposure installation, with at least one fluoride crystal lens is disclosed. A reduction in the detrimental influence of birefringence is achieved if this lens is a (100)-lens with a lens axis which is approximately perpendicular to the {100} crystallographic planes or to the crystallographic planes equivalent thereto of the fluoride crystal. A further reduction in the detrimental influence of birefringence is obtained by covering an optical element with a compensation coating.

Abstract: The disclosure relates to optical systems, such as illumination devices or projection objectives of microlithographic projection exposure apparatuses, that include at least one optical element having at least one curved lens surface which carries an interference layer system. The interference layer system includes an alternating sequence of layers. At least one of the layers is subdivided by at least one intermediate layer having a thickness of not more than 5 nanometers. A column structure which is formed in the at least one subdivided layer is interrupted by the at least one intermediate layer.

Abstract: In a projection objective provided for imaging a pattern arranged in an object plane of the projection objective into an image plane of the projection objective with the aid of an immersion medium arranged between a last optical element of the projection objective in the light path and the image plane, the last optical element has a transparent substrate and a protective layer system that is fitted to the substrate, is provided for contact with the immersion medium and serves for increasing the resistance of the last optical element to degradation caused by the immersion medium.

Abstract: Objective, in particular a projection objective for a microlithography projection-exposure installation, with at least one fluoride crystal lens. A reduction in the detrimental influence of birefringence is achieved if this lens is a (100)-lens with a lens axis which is approximately perpendicular to the {100} crystallographic planes or to the crystallographic planes equivalent thereto of the fluoride crystal. In the case of objectives with at least two fluoride crystal lenses, it is favorable if the fluoride crystal lenses are arranged such that they are rotated with respect to one another. The lens axes of the fluoride crystal lenses may in this case point not only in the <100> crystallographic direction but also in the <111> crystallographic direction or in the <110> crystallographic direction.

Abstract: A method and a device for decontaminating optical surfaces, in particular for decontaminating the surfaces of beam-guiding optics employing UV-radiation in a cleansing atmosphere. The wavelength of the UV-radiation employed falls within a range where oxygen strongly absorbs and the cleansing atmosphere has an oxygen concentration less than that of air. The method and device have application to, e.g., cleaning the surfaces of the beam-guiding optics of microlithographic projection-exposure systems.

Abstract: A method and a device for decontaminating optical surfaces, in particular for decontaminating the surfaces of beam-guiding optics employing UV-radiation in a cleansing atmosphere. The wavelength of the UV-radiation employed falls within a range where oxygen strongly absorbs and the cleansing atmosphere has an oxygen concentration less than that of air. The method and device have application to, e.g., cleaning the surfaces of the beam-guiding optics of microlithographic projection-exposure systems.