Nonlinear optical properties/effects

There have been some attempts to compute nonlinear optical properties in solution. These studies have shown that very small variations in the solvent cavity can give very large deviations in the computed hyperpolarizability. The valence bond charge transfer (VB-CT) method created by Goddard and coworkers has had some success in reproducing solvent effect trends and polymer results (the VB-CT-S and VB-CTE forms, respectively). 

Liquid crystal polymers are also used in electrooptic displays. Side-chain polymers are quite suitable for this purpose, but usually involve much larger elastic and viscous constants, which slow the response of the device (33). The chiral smectic C phase is perhaps best suited for a polymer field effect device. The abiHty to attach dichroic or fluorescent dyes as a proportion of the side groups opens the door to appHcations not easily achieved with low molecular weight Hquid crystals. Polymers with smectic phases have also been used to create laser writable devices (30). The laser can address areas a few micrometers wide, changing a clear state to a strong scattering state or vice versa. Future uses of Hquid crystal polymers may include data storage devices. Polymers with nonlinear optical properties may also become important for device appHcations. 

Crystals with one of the ten polar point-group symmetries (Ci, C2, Cs, C2V, C4, C4V, C3, C3v, C(, Cgv) are called polar crystals. They display spontaneous polarization and form a family of ferroelectric materials. The main properties of ferroelectric materials include relatively high dielectric permittivity, ferroelectric-paraelectric phase transition that occurs at a certain temperature called the Curie temperature, piezoelectric effect, pyroelectric effect, nonlinear optic property - the ability to multiply frequencies, ferroelectric hysteresis loop, and electrostrictive, electro-optic and other properties [16, 388],... 

While the linear absorption and nonlinear optical properties of certain dendrimer nanocomposites have evolved substantially and show strong potential for future applications, the physical processes governing the emission properties in these systems is a subject of recent high interest. It is still not completely understood how emission in metal nanocomposites originates and how this relates to their (CW) optical spectra. As stated above, the emission properties in bulk metals are very weak. However, there are some processes associated with a small particle size (such as local field enhancement [108], surface effects [29], quantum confinement [109]) which could lead in general to the enhancement of the fluorescence efficiency as compared to bulk metal and make the fluorescence signal well detectable [110, 111]. 

P. Ye and Y. R. Shen, Local field effect on linear and nonlinear optical properties of... 

Nonlinear Optical Effects Fluorine substitution can modify nonlinear optical properties of materials and is useful in providing synthetic attachment points for NLO groups. ... 

A more comprehensive discussion of the theoretical background can be found in the first part of this review.1 This necessarily more abbreviated account focuses on those aspects relevant to third-order properties. As discussed in the first part,1 a convenient way to describe the nonlinear optical properties of organic molecules is to consider the effect on the molecular dipole moment p of an external electric field ... 

The D-PS-A systems investigated for their ability to yield charge-separated states possess suitable features (see Section 8.2.3). Ion-dependent optical changes produced by indicator ligands [8.34-8.40] could lead to ion-selective control of nonlinear optical properties. Molecular electron donor-acceptor complexes may present NLO effects since they possess polarized ground states and undergo inter-... 

At the end of the 1960 s, the Kurtz and Perry powder SHG method was introduced.(8) For the first time, rapid, qualitative screening for second order NLO effects was possible. The stage was set for a rapid introduction of new materials, both inorganic and organic. The early history summarized here is based on a more extensive report presented by Zyss and Chemla (8) in their series "Nonlinear Optical Properties of Organic Molecules and Crystals."... 

Nonlinear optical (NLO) properties are usually considered to depend on the intrinsic features of the molecule and on the arrangement of a material. An intermediate level of complexity should also be taken into account, that of the formation of well-defined supermolecules, resulting from the association of two or more complementary components held together by a specific array of intermolecular interactions (1). Such intermolecular bonding may yield more or less pronounced NLO effects in a variety of supramolecular species (2). Thus, three levels of nonlinear optical properties may be distinguished the molecule, the supermolecule and the material. The molecular and supramolecular levels involve respectively - intramolecular effects and structures, -... 

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. 

Bishop s attention turned to accurate calculations of electrical and magnetic properties, especially those of importance in nonlinear optics. Since most experiments in this field measure ratios, not absolute values, it is necessary to have a calculated value. Universally, Bishop s helium nonlinear optical properties are used. In the same field, he was the first to seriously investigate the effects of electric fields on vibrational motions, with a much-quoted paper.65 His theory and formulation has now been added to two widely used computational packages HONDO and SPECTROS. He has also derived a rigorous formula to account for the frequency dependence (dispersion) in nonlinear optical properties.66 He used this theory to demonstrate that the anomalous dispersion in neon, found experimentally, is an artifact of the measurements. 

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