Photorefractive behavior

Refractive Index Modulation by Esc- Photorefractive behavior in polymers can be very roughly modeled by assuming a one-dimensional index of refraction change caused by the vector siun of the applied bias field and a space-charge field resulting from separated, trapped charges within the material... 

The synthetic methodology we developed is characterized by "high fidelity" and is adaptable to allow the preparation of a "catalog" of polymers. This latter aspect is potentially important for systematic structure-property investigations in which the CT and/or NLO toctionalities can quite easily be systematically varied. These polymers, when doped with CG dopants, are expect to exhibit photorefractive behavior. 

Note 3 A polymer that exhibits a nonlinear optical effect due to anisotropic electric susceptibilities when subjected to electric field together with light irradiation is called an electro-optical polymer. A polymer that exhibits electro-optical behavior combined with photoconductivity is called a photorefractive polymer. 

The field of photorefractivity in organic polymers and glasses has been in existence for less than a decade. The understanding of charge generation in these materials (which are often composites) is not yet mature, and the behavior of some of the more common constituents is understood better. Much of the literature on photo-refraetivity deseribes free earrier generation quantum efficiency measurements only briefly, before a more detailed discussion of other factors such as mobility and electro-optic response. Some of the relevant information pertinent to free carrier generation in these materials is presented here, to be followed by a review of this aspect of the amorphous photorefractives literature. 

We noted earlier that when two light beams cross each other, photons in one beam do not affect those in the other beam. This is normally the case, but when the incident light beams are two intense laser beams, the first laser beam will alter the optical behavior of the material so that the second laser beam will behave differently from the first. When two laser beams of the same frequency intersect, they interfere and produce a pattern of light that varies sinusoidally through the crystal. If the crystal is photorefractive, the refractive index of the crystal will also be distorted in a sinusoidal manner (but with a 90 phase shift). As the beams pass through the crystal they may interfere with each other so that one beam, by constructive interference, gains intensity, while the other, by destructive interference, loses it. Effects such as these may provide important technology. 

The present studies are mainly devoted to silicon carbide (SiC)-based materials in the form of isolated clusters, nanopartides, or several architectures, which exhibit various original features. The interests in SiC is motivated by the large offered possibihties from structural aspects as well as physical responses such as electronic, optics, photovoltaic or dielectric properties. Additionally, beyond good thermal stability and mechanical hardness, the SiC is versatile from structural aspect (more than 170 polytypes), electronic behavior (a variable energy gap from 2.4 to 3.3 eV) as well as photorefractive properties (Vonsovici et al. 2000). As matter of fact, the nanocrystalline size modulates all the intrinsic parameters involved in the parent bulk materials. When nanopartides are associated with suitable matrixes, promising new potentialities... 

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