Reflective optical element and optical system for EUV lithography having proportions of substances which differ across a surface

A reflective optical element for an extreme ultraviolet (EUV) wavelength range, comprising:

• a substrate having a surface, and
• a multilayer system that extends over the surface of the substrate,
• wherein the multilayer system comprises at least two alternating layers
• composed of at least two different materials with mutually differing real parts of the refractive index at a wavelength in the EUV wavelength range,
• wherein a given one layer of one of the at least two materials and a further layer or layers arranged between the given one layer and another layer, which is closest at an increasing distance from the substrate, of a same material as the material of the given one layer form a stack,
• wherein, in the stack, the material of the layer with the lower real part and/or the material of the layer with the higher real part of the refractive index is a combination of at least two substances,
• wherein respective proportions of the at least two substances in the combination differ between at least one partial surface of the multilayer system and a remaining surface of the multilayer system.