Surface nonlinear optical polarization

The surface nonlinear optical polarization of second order can be written in the form [34]... 

By using a nonlinear optical process such as SHG, one can probe surface phonons and adsorbate-related vibrations exclusively [14,15,32,34]. Time-resolved SHG (TRSHG) detects the second harmonic (SH) of the probe beam as a function of time delay between pump and probe. The SH electric field is driven by the nonlinear polarization Pi 2w) at the surface, which... 

Comparison of Linearly and Circularly Polarized Probes of Nonlinear Optical Activity of Chiral Surfaces... 

In this introductory chapter the concepts of linear and nonlinear polarization are discussed. Both classical and quantum mechanical descriptions of polarizability based on potential surfaces and the "sum over states" formalism are outlined. In addition, it is shown how nonlinear polarization of electrons gives rise to a variety of useful nonlinear optical effects. 

Nonlinear p-polarized polaritons for b = 0 were considered under the same conditions (20). The papers cited revealed the dispersion laws of nonlinear waves of s and p types. Their most significant features are the non-monotonic dependence of the field amplitudes on z and the dependence of the frequencies of these waves on the field amplitude at the boundary (i.e. at z = 0). We do not go into details of the calculations here. We emphasize only that the transition layer, which can also be optically nonlinear, was ignored in these papers. Taking into account the nonlinearity in the transition layer results in the dependence of surface wave characteristics on the field at the interface, and this special case has been dealt with (22), (23) in connection with the problem of self-focusing of surface polaritons. 

The theoretical framework developed above is valid in the electric dipole approximation. In this context, it is assumed that the nonlinear polarization PfL(2 >) is reduced to the electric dipole contribution as given in Eq. (1). This assumption is only valid if the surface susceptibility tensor x (2 > >, a>) is large enough to dwarf the contribution from higher orders of the multipole expansion like the electric quadrupole contribution and is therefore the simplest approximation for the nonlinear polarization. At pure solvent interfaces, this may not be the case, since the nonlinear optical activity of solvent molecules like water, 1,2-dichloroethane (DCE), alcohols, or alkanes is rather low. The magnitude of the molecular hyperpolarizability of water, measured by DC electric field induced second harmonic... 

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