Electronic second-order nonlinearity

In order to describe the second-order nonlinear response from the interface of two centrosynnnetric media, the material system may be divided into tlnee regions the interface and the two bulk media. The interface is defined to be the transitional zone where the material properties—such as the electronic structure or molecular orientation of adsorbates—or the electromagnetic fields differ appreciably from the two bulk media. For most systems, this region occurs over a length scale of only a few Angstroms. With respect to the optical radiation, we can thus treat the nonlinearity of the interface as localized to a sheet of polarization. Fonnally, we can describe this sheet by a nonlinear dipole moment per unit area, -P ", which is related to a second-order bulk polarization by hy P - lx, y,r) = y. Flere z is the surface nonnal direction, and the... 

The n-electron excitations are viewed as occuring on molecular sites weakly coupled to their neigbors and providing sources of nonlinear optical response through the on-site microscopic second order nonlinear electronic susceptibility... 

In summary, we have briefly reviewed current research highlights from studies of second order nonlinear optical responses in organic and polymeric media. We have stressed how fundamental studies have led to microscopic understanding of important electronic states that comprise the origin of the large second order nonlinear responses in these... 

For second-order nonlinear polarization, the problem becomes more complex. As can be seen in Figure 13 the anharmonic polarization shows the largest deviation from the linear polarization with large distortion values. Therefore, if the material is not polarizable (i.e., if the electrons can only be perturbed a small distance from their equilibrium positions), then the anharmonicity will not be manifested. For large second-order nonlinearities we need a material that offers both a large linear... 

The EO effect is a second-order nonlinear optical (NLO) effect. Only non-centrosymmetrical materials exhibit second-order NLO effects. This non-centrosymmetry is a condition, both at the macroscopic level of the bulk arrangement of the material and at the microscopic level of the individual molecule. All electro-optic modulators that are presently used by telecom operators are ferro-electric inorganic crystals. The optical nonlinearity in these materials is to a large fraction caused by the nuclear displacement in the applied electric field, and to a smaller fraction by the movement of the electrons. This limits the bandwidth of the modulator. The nonlinear response of organic materials is purely electronic and, therefore, inherently faster. 

Following the same procedure outlined for the cold plasma, we can specialize the system of (10.17) and (10.18) in Part I to the one-dimensional case with circular polarization and zero group velocity. The explicit forms of the relevant equations are given in [39], where RES in an electron-positron plasma were studied. Since the two species have equal masses and absolute values of charge, the plasma does not develop any charge separation for Te = Tp = T0 and so (j> 0. A single second-order nonlinear differential equa-... 

Metallocenyl fragments have been incorporated as electron donor units into various NLO materials. In most of the studies of these systems, the metal-ring interaction is not the focus of interest, and only a few have systematically examined the effects that ring substituents have on the second-order nonlinearities and related them to changes in metal-ring... 

Lindsay, G. A. and Singer, K. D. (eds) (1995). Polymers for Second-Order Nonlinear Optics. ACS Symposium Series. American Chemical Society, Washington, DC Liptay, W. (1969). Angew. Chem. 81, 195 Angew. Chem. Int. Ed. Engl. 8, 177 Liptay, W. (1974). Excited States, Vol. 1. Dipole Moments and Polarizabilities of Molecules in Excited Electronic States (ed. E. C. Lim). Academic Press, New York, p. 129... 

Tancrez, N., Eeuvrie, C., Ledoux, I., Zyss, J., Toupet, L., Le Bozec, H. et al. (2005) Lanthanide complexes for second order nonlinear optics evidence for the direct contribution of /-electrons to the quadratic hyperpolarizability. Journal of the American Chemical Society, 127 (39), 13474-13475. 

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