NONLINEAR-OPTICAL RESPONSE DUE TO RESONANT ENHANCEMENT OF THE INTERNAL FIELD WITH PARTICULAR SPATIAL-DISTRIBUTION

Peculiar properties of nonlinear response, due to a resonant enhanceme nt of internal field are predicted for the mesoscopic systems by means of a nonlocal theory of nonlinear response. in this theory, self-cons istent motions of the internal field and the induced polarization, whi ch are related nonlocally with each other, are determined by solving t he equation system of Schrodinger and Maxwell's equations. A study wit h a model of ultrathin films consisting of one-dimensional Frenkel exc itons has clarified the following points: As a result of a self-consis tent motion with the induced polarization, the internal field with a c haracteristic spatial distribution associated with each quantized exci ton state is enhanced at a particular resonant energy including a radi ative correction that depends on system size. This resonant enhancemen t of the internal field greatly strengthens the nonlinear signal of a particular third-order process, leading to a remarkable size and energ y dependence of the nonlinear response. This effect is explicitly demo nstrated for a particular type of pump-probe spectroscopy.