Nonlinear optical response due to resonant enhancement of the internal field with particular spatial distribution

Peculiar properties of nonlinear response, due to a resonant enhancement of internal field are predicted for the mesoscopic systems by means of a nonlocal theory of nonlinear response. in this theory, self-consistent motions of the internal field and the induced polarization, which are related nonlocally with each other, are determined by solving the equation system of Schrodinger and Maxwell's equations. A study with a model of ultrathin films consisting of one-dimensional Frenkel excitons has clarified the following points: As a result of a self-consistent motion with the induced polarization, the internal field with a characteristic spatial distribution associated with each quantized exciton state is enhanced at a particular resonant energy including a radiative correction that depends on system size. This resonant enhancement of the internal field greatly strengthens the nonlinear signal of a particular third-order process, leading to a remarkable size and energy dependence of the nonlinear response. This effect is explicitly demonstrated for a particular type of pump-probe spectroscopy.