Absorption of light by plasmons in a nanoporous metal slab

We have calculated the absorption spectra of a metal surface with a two-dimensional lattice of spherical voids beneath the surface. It is shown that almost total resonant absorption of light occurs at the plasma resonance in the visible when the inter-void spacing and void lattice depth in the metal substrate are thinner than the skin depth, which ensures the optimal coupling of void plasmons to external light. We conclude that the absorption and local-field properties of a nanoporous metal surface can be effectively tuned by nano-engineering of spherical pores. This makes the nanoporous metal surface very attractive for various applications in future submicron light technology.