Metallic multilayers for x rays using classical thin-film theory

TLDR

The performance of X–UV mirrors depends on manufacturing tolerances, which vary with spectral range and material refractive index, and on interface roughness that can significantly reduce reflectivity. The paper investigates the impact of manufacturing tolerances and interface roughness on X–UV mirror performance. The authors develop a reflectance calculation method that incorporates interface roughness to assess sensitivity. Successive evaporation of two carefully selected elements enables highly efficient X–UV mirrors, and specular reflectance at 0.159 nm is highly sensitive to layer roughness.

Abstract

Successive evaporation of two correctly chosen elements now make possible highly efficient X–UV mirrors. However, good results depend on two points: First we must know the manufacturing tolerances; these depend strongly on the spectral range and the refractive index of materials used for the coating. The other important parameter is the roughness of each interface, which can result in significant losses in the reflectivity of the mirrors. This paper examines both points. Specular reflectance measurements at 0.159 nm are very sensitive to the roughness of each layer. To demonstrate this sensitivity we develop a method of calculation of this reflectance taking into account the roughness of each interface of the multilayer.