Phenomenological three-layer model for surface second-harmonic generation at the interface between two centrosymmetric media

A three-layer model is presented to account within a single framework for the different contributions to the surface second-harmonic response at the interface between two centrosymmetric media. It is shown that the optical relative permittivity for the intermediate layer can be incorporated in the geometrical factors of the second harmonic response. The problem of the bulk non-local contribution is then discussed within the same formalism and the associated response incorporated into the effective susceptibility tenser. Three particular cases are given as application of the model to experimental procedure.