PROBLEM TO BE SOLVED: To provide an optical mechanism for EUV lithography and a method for configuring the optical mechanism in which deformation due to an influence of temperature is reduced.SOLUTION: A reflective coating 31 is applied to a substrate 32, the reflective coating having a plurality of individual layers that alternately consist of materials having different refractive indices. The reflective coating can also comprise an intermediate layer for preventing diffusion and a capping layer 31a for preventing oxidation or corrosion. The substrate 32 is applied to a carrier 33, in which a plurality of heating elements 33a in the form of Peltier elements are provided; and these elements serve for homogeneously heating the substrate 32 to a use temperature. A temperature sensor 35 is provided laterally on the substrate 32 and is connected to a control device for controlling the temperature of the substrate 32 to the use temperature by a closed loop. Deformations and/or changes in a length of the substrate 32 caused by temperature fluctuations are avoided by controlling the use temperature to correspond as exactly as possible to the zero crossing temperature of the coefficient of thermal expansion of the substrate 32.