Abstract: A method for improving imaging properties of two or more optical elements comprises the step of determining for at least one of the two optical elements a polarization-dependent perturbation. In a further step a polarization-independent perturbation is determined for at least one of the two optical elements. Then a target position for the at least one movable optical element is calculated such that, in the target position, the total perturbation of the at least two optical elements which is made up of the polarization-dependent perturbations and polarization-independent perturbations of the two optical elements, is minimized. Finally the at least one movable optical element is moved the to the calculated target position.

Abstract: A method for improving imaging properties of two or more optical elements comprises the step of determining for at least one of the two optical elements a polarization-dependent perturbation. In a further step a polarization-independent perturbation is determined for at least one of the two optical elements. Then a target position for the at least one movable optical element is calculated such that, in the target position, the total perturbation of the at least two optical elements which is made up of the polarization-dependent perturbations and polarization-independent perturbations of the two optical elements, is minimized. Finally the at least one movable optical element is moved the to the calculated target position.

Abstract: Centimeter thick plates or lenses made from calcium fluoride or barium fluoride with beam propagation in the direction of the <110> crystal direction or of a main axis equivalent thereto are provided as retardation elements for the deep ultraviolet. They can be installed in an unstressed fashion. In a particular embodiment a retardation plate comprises a birefringent crystal plate which has an entry face and an exit face for incident and emerging light, respectively. A form-birefringent dielectric layer structure is applied to the entry and/or exit face. It may, for example, be a periodic sequence of at least two layers with alternating refractive indices. The retardation plate is suitable for ultraviolet light, and permits a large range of angles of incidence. Retardation elements according to the invention are particularly suitable for microlithography at 157 nm.