Amplification of local fields in disordered metallic structures

Amplification of higher-order multipole optical fields can exist for a nanometre-size object emitting in a complex metallic environment. Frequencies and symmetries which would not be normally observed in the far-field, because of their weakness, become activated by the interactions of the object with the local collective plasmon resonances of the immediate environment (and its inhomogeneities). This idea can provide a simple and purely electromagnetic explanation to some of the most puzzling aspects of fluctuations and activation of forbidden modes observed in some types of spectroscopies involving metallic nanostructures, such as surface-enhanced Raman scattering.