Nonlinear optical effects, analysis

In the following sections we will first in Section 2 briefly discuss the necessary background to understand optical activity effects in linear and nonlinear optics and to illustrate the similarities and differences between both types. In Section 3 we present a more thorough analysis of nonlinear optical effects in second-harmonic generation, both from a theoretical and an experimental point of view. Section 4 deals with experimental examples that illustrate the usefulness of nonlinear optical activity in the study of chiral thin films and surfaces. Finally, in Section 5 we give an overview of the role of chirality in the field of second-order nonlinear optics and show that chiral molecules can be useful for applications in this field. 

Goals and objectives of the study. Objective to establish a relationship between the optical and magnetic properties, systematic scientific analysis of the nature of the interaction of metals with fullerenes, the smdy of nonlinear optical effects of porphyrins, fullerenes and carbon nanostrucmres. 

Experimental Pitfalls. Several types of systematic inaccuracies in nonlinear optical susceptibility characterization techniques have appeared in the literature due to incomplete analysis of propagation effects. It is believed that use of the above models make them more obvious. Some examples are described in this section. 

In nanocomposite media, is worth about a few picoseconds (see 8.3.2.3 below). Eq. (30) then helps explaining the fact that, as noticed in the preceding section, xOl values measured with femtosecond pulses are smaller than those obtained with longer pulsewidths. However, dynamical thermal effects are likely to play a crucial role in the material nonlinear optical response, as will be shown in tire following. As their influence depends on the excitation temporal regime, the measurement analysis is not as simple as one could expect from the only characteristic time comparison of Eq. (30). We now go deeper into these thermal effects. 

Molecular electronics uses molecular materials in which the molecules retain separate identities. As a result, the properties of such materials depend on the molecular arrangement, properties, and interactions. Theory seeks to guide the design and synthesis of effective molecular materials. It does so by analysis, interpretation, and prediction, leading to the development and evaluation of concepts, models, and techniques. The role of theory in treating molecular properties (mainly by molecular orbital methods) and arrangement (by electromagnetic or quantum-mechanical approaches) is of importance. When these factors are combined, the material properties can be treated more successfully in cases where the interactions are not essential in, e.g., in nonlinear optics as opposed to electronic transport properties. 

In this section we report a second extract of the study we have published on the Journal of the American Chemical Society about solvent effects on electronic and vibrational components of linear and nonlinear optical properties of Donor-Acceptor polyenes. In a previous section we have presented the analysis on geometries, here we report the results obtained for the electronic and vibrational (in the double harmonic approximation) static polarizability and hyperpolarizability for the two series of noncentrosym-metric polyenes NH2(CH=CH) R (n=l,2), with R=CHO (series I) and with R=N02 (series II) both in vacuo and in water. 

Cascading. In most cases, the distinction between second- and third-order nonlinearities is evident from the different phenomena each produce. That distinction blurs, however, when one considers the cascading of second-order effects to produce third-order nonlinear phenomena (51). In a cascaded process, the nonlinear optical field generated as a second-order response at one place combines anew with the incident field in a subsequent second-order process. Figure 2 shows a schematic of this effect at the molecular level where second-order effects in noncentrosymmetric molecules combine to yield a third-order response that may be difficult to separate from a pure third-order process. This form of cascading is complicated by the near-field relationships that appear in the interaction between molecules, but analysis of cascaded phenomena is of interest, because it provides a way to explore local fields and the correlations between orientations of dipoles in a centros5nnmetric material (52). 

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