Abstract

The paper will review the present state-of-the-art of multilayer optics. Different theories to model the performance of multilayer structures will be compared and the influence of imperfections will be discussed. Optimized coating designs for the XUV will be compared to perfect crystals, as used in x-ray diffraction and laser mirrors, as used for visible light. Practically all deposition methods have been used for the fabrication of x-ray multilayer structures and we will summarize their strengths and weaknesses. Material combinations for a specific application are first selected by the optical constants at a specific wavelength and then by the requirement that the materials chosen must form atomically abrupt, smooth and stable boundaries. Only a handful of combinations are in practical use. The limit on the performance of multilayer structures is given by absorption and by the roughness of the boundaries. The shortest practically useful multilayer period (Λ ≈ 25Å) is limited by boundary roughness and a drastic improvement at shorter periods can only be expected if we learn to place atoms by a non-random process.

© 1992 Optical Society of America