Abstract

Zero-reflectivity surfaces on lossy materials are useful for eliminating unwanted reflections. Surface-relief gratings on metal surfaces can produce unity transmissivity and thus total absorption. A rigorous impedance matching approach is used. The zero reflectivity condition and the equivalence of the homogeneous layer and the grating in the long-wavelength limit produce a system of nonlinear transcendental equations. First, the required thickness and complex refractive index for a single homogeneous lossy layer antireflection coating are calculated. Then the filling factor and groove depth of the equivalent high-spatial-frequency rectangular-groove surface-relief grating are determined. The analysis includes multiple dielectric overlayers for grating protection and for broad banding the antireflection characteristics. It is shown that multiple zero reflectivity solutions exist for both TE and TM polarizations for arbitrary angles of incidence and for any complex refractive-index substrate. Necessary and sufficient conditions in the parametric space are also computed. The inclusion of one or more dielectric overlayers gives additional design flexibility. The sensitivity of the antireflection design as a function of the angle of incidence and wavelength is presented.

© 1987 Optical Society of America