Third-order nonlinear optical effects

Just as second-order effects involve the interaction of two electric fields with the electrons of a material, third-order effects involve three electric fields, 1 2 and 3. In the special case where all these three fields have the same frequency and where y(21 is zero (which is necessarily the case in centrosymmetric materials -see Section 11.1.2), we see that 

The molecular 2PA cross-section is sometimes denoted by a2 or of rather than d, while the corresponding bulk 2PA coefficient is, rather confusingly, typically represented by ft. 

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Fig. 8. Examples of some of the donor-acceptor substituted TEEs prepared for the exploration of structure-property relationships in the second- and third-order nonlinear optical effects of fully two-dimensionally-conjugated chromophores. For all compounds, the second hyperpolarizability y [10 esu], measured by third harmonic generation experiments in CHCI3 solution at a laser frequency of either A = 1.9 or 2.1 (second value if shown) pm is given in parentheses. n.o. not obtained...

For the application of QDs to three-dimensional biological imaging, a large two-photon absorption cross section is required to avoid cell damage by light irradiation. For application to optoelectronics, QDs should have a large nonlinear refractive index as well as fast response. Two-photon absorption and the optical Kerr effect of QDs are third-order nonlinear optical effects, which can be evaluated from the third-order nonlinear susceptibility, or the nonlinear refractive index, y, and the nonlinear absorption coefficient, p. Experimentally, third-order nonlinear optical parameters have been examined by four-wave mixing and Z-scan experiments. 

Third-order nonlinear optical effect in polyarylenevinylene cast films prepared by via-precursor method... 

Third-Order Nonlinear Optical Effects in Molecular and Polymeric Materials... 

Extensive ir-conjugation is also often associated with enhanced conductivity in organic systems (6). Polyacetylene and polythiophene which in the doped state exhibit very high electrical conductivity also exhibit relative large third-order nonlinear optical effects in... 

Third-order nonlinear optical effects are described by the tensors xfh and y j. In contrast to second-order nonlinearities y fk and Yijk>no symmetry requirements are imposed on these effects to occur. Some authors do not include the faculty denominators of the Taylor expansion in nonlinearity definitions of Eqs. (4) and (5). 

On the route to all-optical signal processing the development of materials with large third-order nonlinear optical effects is of decisive importance. For the material characterization and the assessment of its usefulness for applications the absolute value of the third-order nonlinear optical susceptibility y has to be known. Since most measurements are performed relative to a reference material, the establishment of a well accepted value for a standard material is important. 

Azo-benzene molecules are widely recognized as attractive candidates for many nonlinear optical applications. A highly deformable distribution of the ic-electron gives rise to very lar molecular optical nonlinearitics, Phdto-isomerization of azo molecules allows linear and nonlinear macroscopic susceptibilities to be easily modified, giving an opportunity to optically control the nonlinear susceptibilities. In this chapter, we will discuss third-order nonlinear optical effects related to photoisornerization of azo-dye polymer optical materials. 

Substituting the expansion (3.197) into (3.19) and (3.29) we obtained the desired expansion of the Hamiltonian in powers with respect to Bose operators, when not only the dynamic, but also the kinetic interaction is taken into account. The new anharmonicity terms do not contain kinematic corrections. The role of this anharmonicity in the theory of third order nonlinear optical effects has been discussed in the article by Ovander (92). 

For third-order nonlinear optical effects, the structural requirements are different. Extended 7r-conjugation is found to enhance the nonlinearity. Consequently, conjugated polymers have emerged as an important class of... 

The area of third-order nonlinear optical effects in organic systems has been a focus of attention only recently. Consequently, on a relative basis, this area is not as well explored. Here the.limitation to device production is due to both the low magnitude of quality required for device structures. 

Although third-order nonlinear optical effects are much weaker, several studies of tgiij g- processes in L-B films have successfully been performed, A third harmonic generati[Pg.576]

U. Gubler, Third Order Nonlinear Optical Effects in Polymers, Ph. D. dissertation, Swiss Fed. Inst. Tech., Zurich, 2000. Available at http //ecollection.ethbib.ethz.ch/cgi-bin/show.pl type = diss nr = 13605 (Accessed September 12, 2003). 

A further third-order nonlinear optical effect is the TPA, where a molecule is able to absorb two photons simultaneously to reach an excited state. The energy difference between the excited and ground state relate exactly to the energy of the photons. 

Polydiacetylenes are particularly interesting for their optical and electrical properties. For example, large third-order nonlinear optical effects can be produced. Extensive electronic conjugation is required for such behaviour and polydiacetylenes produce the largest values yet observed for example, the solid state polymer of (20) exhibits a value of esu, and the LB polymer of (10) with n = 16,m = S exhibits a non-resonant value of 4 x 10 esu. Insulating properties are... 

Third-order nonlinear optical effects, such as third-harmonic generation or other kinds of four-wave mixing phenomena, occur in all media, irrespective of their symmetry. This follows from the parity-even property of the corresponding tensors. Consequently, third-harmonic generation can be observed both in... 

Third-order nonlinear optical effects are also of interest to physicists and communications engineers. Relatively little work has been directed at developing third-order materials until recently and only a few studies have concentrated on LB films. A good example of one such study is that performed by Saito and TsutsuF in which... 

THIRD ORDER NONLINEAR OPTICAL EFFECTS IN CONJUGATED POLYMERS... 

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