Zero-reflectivity homogeneous layers and high spatialfrequency surface-reliefgratings on lossy materials.

The required thickness and complex refractive index of single homogeneous layers on lossy substrates to produce zero reflectivity are calculated by a rigorous impedance matching approach. The analysis is applicable to both TE and TM polarization and to any angle of incidence. The filling factor and groove depth of a rectangular-groove grating, equivalent to a single homogeneous lossy layer in the long-wavelength limit, are calculated. The method reduces to that previously found for dielectric surface-relief gratings in the limit of no losses. The antireflection behavior of the gratings is verified using the rigorous (without approximations) coupled-wave analysis of metallic surface-relief grating diffraction. It is shown that multiple zeroreflectivity solutions exist for both TE and TM polarizations and for any angle of incidence for an arbitrary complex-refractive-index substrate. Example zero-reflectivity gold gratings for incident free space wavelengths from 0.44 to 12.0 microm are presented.