Reflective optical element

An optical element, comprising:

• a substrate having first and second sides;
• a multilayer system disposed on the first side of the substrate, the multilayer system comprising at least two alternating materials having a different real part of the refractive index at the working wavelength, wherein the multilayer system includes a first alternating material from the group consisting of thorium, uranium, barium, nitrides thereof, carbides thereof, borides thereof, lanthanum carbide, lanthanum nitride, lanthanum boride, and a second alternating material selected from the group consisting of carbon, boron, boron carbide, or lanthanum as first alternating material and carbon or boron as second alternating material;
• a protective system on the second side of the substrate, the protective system comprising a nitride, an oxide and/or a platinum metal,
• wherein the optical element is reflective for radiation at a wavelength of 1 nm to 12 nm.