Resonant SHG for excitons weakly confined in a slab and its cavity-enhancement effect

The theory for resonant second-harmonic generation in systems with inversion symmetry has been outlined according to a scheme of microscopic nonlocal response, where the internal field and induced polarization are determined self-consistently. An example is given of a Frenkel exciton system in a slab with and without the cavity effect. A remarkable enhancement is shown to occur for a specially designed cavity which contains cavity modes for both fundamental and second-harmonic frequencies.