A mirror, in particular for a microlithographic projection exposure apparatus, has an optically effective surface (10a), a mirror substrate (11) and a reflection layer stack (12) configured to reflect electromagnetic radiation that is incident on the optically effective surface. A metallic diffusion barrier layer (13) is arranged on that side of the reflection layer stack which faces toward the optically effective surface, and a stabilization layer (14) is arranged on the side of the diffusion barrier layer that faces toward the optically effective surface (10a). The stabilization layer reduces deformation of the diffusion barrier layer compared to an analogous structure without such a stabilization layer upon irradiation of the optically effective surface with electromagnetic radiation. The stabilization layer has a porosity, a relative density of which is no more than 80%, where the relative density is defined as the ratio between geometric density and true density.