Mirror, in particular collector mirror for microlithography

A mirror, comprising:

• an optical grating comprising an optically effective mirror surface configured to reflect electromagnetic rays emanating from a first focal point and to focus them onto a second focal point,
• wherein:
• the first and the second focal points lie on a side of the optical grating facing the optically effective mirror surface and define an optical axis;
• the optical grating comprises a plurality of mirror facets;
• each mirror facet comprises a facet surface;
• the facet surfaces define the optically effective surface of the optical grating;
• in a sectional plane that includes the optical axis, the facet surfaces are arranged on a plurality of imaginary elliptical shells displaced from each other along the optical axis;
• common mathematical focus points of the imaginary elliptical shells coincide with the first and second focal points;
• the facet surfaces are distributed along the elliptical shells so that the facet surfaces are arranged at intersection points of the elliptical shells with at least one section of an imaginary circular line;
• and
• for each point on the circular line, a ratio of a distance from the first focal point to the point is the same as a ratio of a distance from the point to the second focal point.