A theoretical analysis of backscattering enhancement due to surface plasmons from multilayer structures with rough interfaces

Backscattering enhancement is a phenomenon in rough surface scattering which manifests itself as a well defined peak in the backscattering direction. In a small roughness regime, backscattering enhancement is induced by the excitation of surface plasmon waves along a certain path followed by their retracing the same path in the reverse direction. In this paper, an accurate solution to two-dimensional scattering from multilayer rough surfaces based on extended boundary condition method and scattering matrix approach is used, which in effect incorporates all orders of scattering. The criteria for observing backscattering enhancement using this method are discussed and the wavenumbers of surface plasmon waves for a two-layer medium are derived. The proposed technique provides rigorous solutions for backscattering enhancement and satellite peaks. Numerical simulations are performed on a dielectric slab deposited on a silver film for both HH and VV polarizations and the emphasis is placed on the effects of subwavelength features of layered rough surfaces on the phenomenon of backscattering enhancement. Particular attention is given to the impact of layer thickness on backscattered enhanced peaks. Finally, the presence of satellite peaks due to the excitation of multiple surface plasmon waves in a layered structure is also demonstrated.