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.

I. Introduction

Scattering from multilayer rough surfaces has been investigated extensively for the past decades in several communities. Analytical solutions based on small perturbation method (SPM) to electromagnetic scattering from a rough surface covered by a homogeneous layer or from a layered medium underneath a rough interface have been presented in [1]–[3]. Recently, the analytical solutions to scattering from two-rough-interface rough surfaces based on small perturbation method (SPM) and Kirchoff approximation (KA) also have been formulated in [4]–[6], respectively. Both theoretical and experimental research efforts have been previously made to study backscattering enhancement effect of rough surfaces due to surface plasmon resonance. Backscattering enhancement finds applications in the study of scattering phenomena from metallic surfaces with a dielectric coating and metallic coated papers. Backscattering enhancement is also an emerging area of interest in biological applications. It has provided a new means to detect and image biological interfaces of thickness well below the diffraction limit.