Surface enhancement of local optical fields and the lightning-rod effect

The increase in the local field E_loc due to the "lightning-rod effect" has been studied theoretically (in a model of a small ellipsoid) and experimentally (by a method of surface-enhanced second-harmonic generation on a surface with protruding needles). Algorithms are proposed for resolving the overall electromagnetic amplification of E_loc into resonant and nonresonant components, both in the model and experimentally. The model predicts a limitation on the nonresonant local-field enhancement because of the modulus of the dielectric constant of the metal. This prediction has been confirmed experimentally.