Multifacet mirrors for the extreme ultraviolet
Until recently, the prospects for efficient normal-incidence reflectors for the extreme-ultraviolet (XUV) spectrum, nominally wavelengths between 10 and 100 nm, have been very limited. In this spectral range, all materials have significant absorption and the index of refraction does not deviate much from unity. The few exceptions with moderately high (≥ 40%) reflectance at 0° include: 1) SIC, either single-crystal or chemically vapor deposited surfaces, with reflectance between 40 and 50% for wavelengths longer than 60 nm, and 2) multilayer interference reflector stacks of Mo and Si films with peak reflectance-performance just over 60% at 13 nm and lower values for designs optimized for adjacent wavelengths between 10 and 20 nm. Indeed, full development of the multilayer option is currently a major goal of a number of research groups around the world.
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