A microscopic view of the electromagnetic properties of sub-λ metallic surfaces

We review the properties of the surface waves that are scattered by two-dimensional sub-λ indentations on metallic surfaces. We show that two distinct waves are involved, a surface plasmon polariton (SPP) and a quasi-cylindrical wave (quasi-CW). We discuss the main characteristics of these waves, their damping characteristic lengths and their relative excitation weights as a function of the separation distance from the indentation and as a function of the metal conductivity. In particular, we derive a closed-form expression for the quasi-CW, which clarifies its physical origin and its main properties. We further present an intuitive microscopic model, which explains how the elementary SPPs and quasi-CWs exchange their energies by multiple scattering to build up a rich variety of near- and far-field optical effects.