A new design technique for multilayer reflectors is presented: It is useful when slight absorption by one or both of the coating materials limits the performance of the reflector. The basic procedure is to add layers to a given substrate or multilayer system one pair at a time. The thickness of each layer is chosen to give the maximum increase in reflectance for each pair of layers added. In general, the optical thicknesses of the layers in each pair are not quarter waves, but depend on the optical constants of the materials, as well as the starting reflectance of the subsystem. By using such optimized pairs, it is possible to exceed the reflectance limit usually imposed on quarter-wave stack reflectors by absorption. Expressions for the optimum design and the ultimate reflectance for a high reflector made with a given set of coating materials are given. Other design techniques found in the literature require more layers to achieve the same level of reflectance as the present method.
© 1980 Optical Society of AmericaPDF Article