Third-order nonlinear optical susceptibility values

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. 

The third-order nonlinear optical susceptibility x was obtained by comparing the measured signals for the sample with that of carbon disulfide as reference under the same experimental condition. The measured x value is 6.2 x 10 esu for the subphthalocyanine at a concentration 1.25 x 10 M. Considering an isotropic media under the Lorenz-Lorentz approximation, the second hyperpolarizability value was found to be 3.0 x 10 esu. Furthermore, A pirc corresponding to the pure subphthalocyanine 17 was calculated to be 6.9 x 10 esu, about four times higher... 

The temporal response of the third-order nonlinear optical susceptibility in poly(PTS) crystal was determined by time-resolved degenerate four-wave mixing (DFWM) by Carter and coworkers. The excited lifetime T ws measured to be 1.8 0.5 ps at 652 nm in the resonant region. The values of phase relxation time T2 measures by Hattori and Kobayashi for a cast film of poly(3BCMU) were 30 and 90 fs for the respective incident... 

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... 

Here, Pq is the permanent polarization, and and denote the second- and third-order nonlinear optical three-dimensional susceptibility tensors. The indices attached to the x tensors refer to the tensor elements, and the indices associated with the E values refer to the components of the electric field strength, here expressed in the laboratory frame. 

The nonlinear optical (NLO) susceptibilities of bioengineered aromatic polymers synthesized by enzyme-catalyzed reactions are given in Tables 2, 3, and 4. Homopolymers and copolymers are synthesized by enzyme-catalyzed reactions from aromatic monomers such as phenols and aromatic amines and their alkyl-substituted derivatives. The third-order nonlinear optical measurements are carried out in solutions at a concentration of 1 mg/mL of the solvent. Unless otherwise indicated, most of the polymers are solubilized in a solvent mixture of dimethyl formamide and methanol (DMF-MeOH) or dimethyl sulfoxide and methanol (DMSO-MeOH), both in a 4 1 ratio. These solvent mixtures are selected on the basis of their optical properties at 532 nm (where all the NLO measurements reported here are carried out), such as low noise and optical absorption, and solubility of the bioengineered polymers in the solvent system selected. To reduce light scattering, the polymer solutions are filtered to remove undissolved materials, the polymer concentrations are corrected for the final x calculations, and x values are extrapolated to the pure sample based on the concentrations of NLO materials in the solvent used. Other details of the experimental setup and calculations used to determine third-order nonlinear susceptibilities were given earlier and described in earlier publications [5,6,9,17-19]. 

In addition to photoconductivity, polysilanes have been found to exhibit marked nonlinear optical properties,95-97 suggesting that they may eventually be useful in laser and other optical technology. The third-order non-linear susceptibility, X3, is a measure of the strength of this effect. The non-linear properties of polysilanes, like the absorption spectra, seem to be dependent on chain conformation and are enhanced for polymers having an extended, near anti conformation (Table 5.5). The value of 11 x 10 12 esu observed for (n-Hex2Si) below its transition temperature is the largest ever observed for a polymer which is transparent in the visible region. 

Copper nanoparticles have been synthesized in silica by 50 keV Cu ion implantation with doses of 8.0x10 ion/cm. N anoparticles were c haracterized by absorption band of surface plasmon resonance in the visible range. Metal nanoparticle composite glasses were analyzed by the Z-scan method at the IR wavelength of NdiYAG laser radiation 1064 nm. The third order nonlinear susceptibility in the analyzed medium with simultaneous nonlinear refraction and absorption were considered as complex values. It is suggested that the samples with nonlinear absorption is perspective ones for optical applications. 

Optical tuning of polygermanes and mixed polysi-lane/polygermane systems have been discussed.Nonlinear optical effects are of particular interest. Third-order nonlinear susceptibilities (/ ) for thin films of oligo- and polygermanes have been measured.A value of 86 x 10 esu was obtained for copoly(methyl-phenylsilylene/methylphenylgermylene)... 

In order to understand the origin of the high values of the third-order nonlinearity observed, we picked polybenzidine for more detailed study. The real and imaginary components of the third-order susceptibility x are measured separately. The real part Rex leads to nonlinear refraction, and the imaginary part Imx ) is responsible for nonlinear absorption. The nonlinear-optical measurements were made using dilute solutions of the polymer in DimethyLsulfoxide/Methanol in the ratio 4 1 (DMSO MeOH). 

In summary, polyaniline was S3mthesized by an enzymatic process and optical properties, including third order nonlinear susceptibility was assessed, x values as high as 7.6x10" (esu) were observed for one of the poljmiers. Based on the time-resolved nonlinear optical response of the poljmier solutions to the laser pulse delay, the electronic nonlinearity is the major component of the x values observed. 

Nonlinear optical properties of homopolymers and copolymers synthesized by enzyme-catalyzed reactions in monophasic media are given in Table 2. Aromatic monomers used for the polymerizations are aniline, aniline derivatives, and phenol derivatives. The table also gives x values of a number of monomers (used in the polymerization reactions) and solvent mixtures used to prepare polymer solutions for the measurements. In general, the third-order susceptibilities of all monomers and solvents tested are very low and are in the neighborhood of 10" esu. The values of the aromatic polymers obtained are three to five orders higher than the values of the monomers. Third-order nonlinear susceptibilities of homopolymers synthesized (by enzyme-catalyzed reactions) from aromatic amines such as aniline, benzidine, ethylaniline, propylaniline, butylaniline, and dimethy-... 

Table 3.14 Nonlinear refractive index and third-order nonlinear susceptibility values for a variety of semiconductors and optical materials. 

For symmetry reasons, the first macroscopic nonlinear coefficient is zero in unordered polymer materials. On the other hand, azo-dye polymers can exhibit very large values, which is interesting for applications in optical limiting and optical switching devices. We will consider the relationship between microscopic and macroscopic third-order susceptibilities. The most general equation for this relationship can be written as ... 

Whatever the degree of approximation used in evaluating the effective nonlinear susceptibility of a composite medium, it can be seen in Eqs. (22), (23) or (27) that the result depends on the product of two complex quantities One linked with the medium morphology and composition (the local field factor), the other linked with the nonlinear optical properties of the metal inclusions themselves (the intrinsic third-order susceptibility, Xm ) - inasmuch as the own contribution of the host matrix to the whole nonlinear response still remains negligible. We will focus here on the second factor. It is noteworthy that very few theoretical work has been accomplished regarding the value of Xm for noble metal nanoparticles after the pioneering smdies of Flytzanis and coworkers [79, 80, 89, 90]. Moreover, as will be underlined below, their results may not be used in every experimental situation as they are. 

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