Abstract: The invention concerns a method for exciting a sub-wavelength inclusion structure, comprising: providing a first medium having a first refractive index ni and a second medium having a second refractive index nt, wherein ni>nt, wherein the sub-wavelength inclusion structure is arranged at a boundary between the first and second media, wherein the sub-wavelength inclusion structure exhibits polarizability properties; and directing light through the first medium towards the sub-wavelength inclusion structure. The angle of the incident light to the normal of the boundary, ?i, is such that, for a given set of: frequency of the light; surface density of inclusions; average polarizability of the inclusion structure at the frequency; first refractive index; and second refractive index, ?i fulfils at least one of the relations for s-polarized light and for p-polarized light described herein.