Third order nonlinear optical properties

Third-order nonlinear properties are also called ur-wave mixing (FWM), because they are related to the interaction of four electromagnetic waves. Although the third-order susceptibility is usually smaller than a high-intensity pump laser can render the third-order signal sufficiently strong to be observable. In the third-order optical process, the polarization can be written as described in Equation 3.131  

For noncentrosymmetric crystals with a 6 mm point group symmetry, such as wurtzite ZnO, the third-order susceptibility tensor (JCsu) has 21 nonzero 

In the case of third harmonic generation, the frequencies of the input beams are the same (coi = CO2 = CO3) and the tripled beam has a frequency CO4 = 3coi. Therefore, for the THG process, Xyu should be invariant when the relative positions ofjkl indices change. Consequently, the number of independent elements of the susceptibility tensor for the THG process I is reduced to just four %xxxx, Xzzzz, Xxxzz, and Xzzxx-Furthermore, when Kleinman symmetry conditions are adopted for experiments performed far from the resonances, one would have x xzz = Xzzxx resulting in only three independent elements [206]. 

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LB films of CO-tricosenoic acid, CH2=CH—(CH2)2qCOOH, have been studied as electron photoresists (26—28). A resolution better than 50 nm could be achieved. Diacetylenic fatty acids have been polymerized to yield the corresponding poly (diacetylene) derivatives that have interesting third-order nonlinear optical properties (29). 

Optical properties of cyanines can be usefiil for both chiral substituents/environments and also third-order nonlinear optical properties in polymer films. Methine-chain substituted die arbo cyanines have been prepared from a chiral dialdehyde (S)-(+)-2-j -butylmalonaldehyde [127473-57-8] (79), where the chiral properties are introduced via the chiral j -butyl group on the central methine carbon of the pentamethine (die arbo cyanine) chromophore. For a nonchiral oxadicarbocyanine, the dimeric aggregate form of the dye shows circular dichroism when trapped in y-cyclodextrin (80). Attempts to prepare polymers with carbocyanine repeat units (linked by flexible chains) gave oligomers with only two or three repeat units (81). However, these materials... 

There have been very few measurements made on the physical properties of Tg derivatives, their relative greater difficulty of preparation when compared with the Tg analogs has meant little interest in their properties. However, TglOSiMeslg has been found to show photoluminescence in the blue region of the spectrum, third-order nonlinear optical properties for TgMeg have been modeled, and electronic properties for and TgMeg have been calculated. 

Third-order nonlinear optical properties of CdTe QDs were examined by Z-scan and FWM experiments in the nonresonant wavelength region. We found that the two-photon absorption cross section, a, is as high as 10 GM, although this value decreases with decreasing size. In addition, the nonlinear response is comparable to the pulse width of a fs laser and the figures of merit (FOM = Re Xqd/ Xqd)... 

Third-order nonlinear optical properties of oriented poly(arylenevinylene) LB films... 

Polydiacetylenes are obtained as single crystals by topochemical solid-state polymerization of the monomer single crystal. These compounds have received considerable attention because of their one-dimensionally -conjugated structure. Their unique --electron structures, and therefore superior third-order nonlinear optical properties, have been extensively investigated. 

Huggins KE, Son S, Stupp SI. Two-dimensional suptamolecular assemblies of a polydiacetylene. 1. Synthesis, structure, and third-order nonlinear optical properties. Macromolecules 1997 30 5305-5312. 

This paper is a tutorial overview of the techniques used to characterize the nonlinear optical properties of bulk materials and molecules. Methods that are commonly used for characterization of second- and third-order nonlinear optical properties are covered. Several techniques are described briefly and then followed by a more detailed discussion of the determination of molecular hyperpolarizabilities using third harmonic generation. 

Model Polymers with Distyrylbenzene Segments for Third-Order Nonlinear Optical Properties... 

D. M. Bishop,/. Chem. Phys., 90, 3192 (1989). General Dispersion Formulae for Molecular Third-Order Nonlinear Optical Properties. 

Tetraethynylethene molecular scaffolding has provided conjugated materials with properties that are greatly enhanced upon incorporating functional arene units. Indeed, third-order nonlinear optical properties are increased by aryl groups photochemical cis-trans isomer-... 

Since Chapter 6 (352) in this volume is devoted to the luminescence and photochemistry of dithiolene complexes, these aspects will not be developed here. In this section, we restrict ourselves to the review of dithiolene complex-based compounds exhibiting optical properties, such as strong infrared (IR) absorption and second- and third-order nonlinear optical properties. In the last part of this section, we will review the use of some dithiolene complexes for optical data storage (printers, developer, CD-ROM, etc.). Contrary to what was observed throughout the two previous sections, no particular dithiolene complex really dominates the domain of the molecular materials exhibiting interesting optical properties. 

Conjugated polymers satisfy these requirements and have thus emerged as the most widely studied materials for their susceptability. Some of the examples of conjugated polymers, that have been studied for their third order NLO properties, are polydiacetylenes, poly-p-phenylenevinylenes and polythiophenes. However, CVD has only been used in the case of poly-p-phenylenevinylenes (PPV) [section 3.4], although values have not been reported. An excellent review of third order nonlinear optical properties of PPV in general, can be found in literature. Recently, McElvain et al. ° reported the values of CVD polyazomethines to be... 

Donor/acceptor substituted azobenzenes, which have large second-and third-order nonlinear optical properties, show a fast thermal Z-F (cis-trans) conversion. 

Enzymatically synthesized polyphenol derivatives are expected to have great potential for electronic applications. The surface resistivity of poly(p-phe-nylphenol) doped with nitrosylhexafluorophosphate was around 105 Q.4a The iodine-labeled poly(catechol) showed low electrical conductivity in the range from 10 6 to 10 9 S/cm.48 The iodine-doped thin film of poly (phenol- co- tetradecyloxyphenol) showed a conductivity of 10 2 S/cm, which was much larger than that obtained in aqueous 1,4-dioxane.24a The third-order optical nonlinearity (%3) of this film was 10 9 esu. An order of magnitude increase in the third-order nonlinear optical properties was observed in comparison with that prepared in the aqueous organic solution. 

Aniline and its derivatives were oxidatively polymerized by peroxidase catalyst. HRP catalyzed the polymerization of aniline in aqueous organic solvents to produce the polymer with a complicated structure in low yields.65 The resulting polymer showed good third-order nonlinear optical properties.66... 

Osaheni and Jenekhe reported a synthesis of conjugated rigid-rod polymers and their NMR data. The conjugated rigid-rod polymers have interesting photoconductive, light-emitting and third-order nonlinear optical properties that have some potential for applications in optoelectronics and photonics. 

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