Poly nonlinear materials

For the nonlinear optical response to be stable during processing and operation of chromophore/poly mer materials, the chromophores need to be chemically stable at all temperatures that the system encounters in electric field poling, and should withstand the fabrication steps needed for device fabrication. Usually, during device processing, the temperature can rise up to 250°C, whereas during operation, the material is subject to temperatures around 100°C for long periods of time. 

It has also been shown that a new area of physics has been developed that uses vibrational infrared and Raman intensities for deriving nonlinear optical data for poly-conjugated materials. The NLO data already collected and discussed show the relevance of the method for materials science. 

The cadmium chalcogenide semiconductors (qv) have found numerous appHcations ranging from rectifiers to photoconductive detectors in smoke alarms. Many Cd compounds, eg, sulfide, tungstate, selenide, teUuride, and oxide, are used as phosphors in luminescent screens and scintiUation counters. Glass colored with cadmium sulfoselenides is used as a color filter in spectroscopy and has recently attracted attention as a third-order, nonlinear optical switching material (see Nonlinear optical materials). DiaLkylcadmium compounds are polymerization catalysts for production of poly(vinyl chloride) (PVC), poly(vinyl acetate) (PVA), and poly(methyl methacrylate) (PMMA). Mixed with TiCl, they catalyze the polymerization of ethylene and propylene. 

Even among nonlinear polymers, many of the materials of interest are composed of a preponderance of bifunctional units with only a minority of polyfunctional units. This applies to vulcanized rubber where no more than about 1 or 2 percent of the isoprene units are cross-linked. It also applies to the amylopectin fraction of starch which consists of chains composed of an average of about 20 glucose units, these chains being connected to one another by trifunctional units to yield an irregular branched array to wool consisting of poly-... 

The material system is a Langmuir-Blodgett film of the S enantiomer of a chiral polymer deposited on a glass substrate. The polymer is a poly(isocyanide)30 functionalized with a nonlinear optical chromophore (see Figure 9.14). In this particular system the optical nonlinearity and chirality are present on two different levels of the molecular structure. The chirality of the polymer is located in the helical backbone whereas the nonlinearity is present in the attached chromophores. Hence, this opens the possibility to optimize both properties independently. 

At this time, many of the parameters listed above have not been measured for nonlinear organic materials. Measurement will be necessary for an assessment of the full potential of such materials. To date, only a nonlinear directional coupler has been implemented in a nonlinear polymer, (poly-4BCMU). For this device at 1060 nm, the nonlinear response was dominated by two-photon absorption, and some limited switching attributable to absorption changes was observed (27). More recent work at 1030 nm appeared to show switching attributable to refractive nonlinearities (28). Clearly there is much progress to be made. 

Since semiconductor materials appear to be general candidates for third order effects, it is not surprising that photoconductive charge transfer complexes such as poly(vinyl carbazole)-trinitrofluorenone (PVK-TNF) would exhibit modest DFWM.(142) The observed nonlinearity at 602 nm, a wavelength absorbed by the CT complex, ranges from 0.2 - 2 x 10"11 esu, increasing as the molar fraction of TNF in the complex, PVK TNF, increased. Charge... 

In summary, it appears that poly silanes and polygermanes have large third order nonlinear susceptibilities, particularly for materials containing only a saturated sigma bonded polymer backbone. This is consistent with their large polarizabilities and the extensive sigma delocalization along the backbone. In some instances, the... 

Partially substituted derivatives of polyacetylene are synthesized via the ring-opening metathesis polymerization (ROMP) of cyclooctatetraene (COT) and its derivatives. Certain poly-COT derivatives afford soluble, highly conjugated poly acetylenes. These materials exhibit large third-order optical nonlinearities and low scattering losses. 

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