Nonlinear crystalline materials

Only certain types of crystalline materials can exhibit second harmonic generation (61). Because of symmetry considerations, the coefficient must be identically equal to zero in any material having a center of symmetry. Thus the only candidates for second harmonic generation are materials that lack a center of symmetry. Some common materials which are used in nonlinear optics include barium sodium niobate [12323-03-4] Ba2NaNb O lithium niobate [12031 -63-9] LiNbO potassium titanyl phosphate [12690-20-9], KTiOPO beta-barium borate [13701 -59-2], p-BaB204 and lithium triborate... 

Barium sodium niobium oxide [12323-03-4] Ba2NaNb 02, finds appHcation for its dielectric, pie2oelectric, nonlinear crystal and electro-optic properties (35,36). It has been used in conjunction with lasers for second harmonic generation and frequency doubling. The crystalline material can be grown at high temperature, mp ca 1450°C (37). 

The interest in efficient optical frequency doubling has stimulated a search for new nonlinear materials. Kurtz 316) has reported a systematic approach for finding nonlinear crystalline solids, based on the use of the anharmonic oscillator model in conjunction with Miller s rule to estimate the SHG and electro optic coefficients of a material. This empirical rule states that the ratio of the nonlinear optical susceptibility to the product of the linear susceptibilities is a parameter which is nearly constant for a wide variety of inorganic solids. Using this empirical fact, one can arrive at an expression for the nonlinear coefficients that involves only the linear susceptibilities and known material constants. 

Many current NLO devices are based upon crystalline materials (such as lithium niobate for the electro-optic switch) and nonlinear optical glasses, but there is intense... 

As mentioned above, the powder SHG method is a useful technique for the screening of second-order nonlinear materials. However, because of the sensitivity of the SHG coefficients of crystalline materials to the orientational aspects of the molecular packing and because the measurement is performed on an essentially random distribution of microcrystalline particles, the powder SHG method is not generally useful for obtaining information about molecular hyperpolarizabilities. 

Transition metal acetylides combine the properties of acetylenes with those of the transition metals, offering flexibility in the tuning of structural and electronic properties of both the organic and inorganic constituents. Optimization of the molecular and bulk crystalline properties is envisaged to lead to a new class of useful nonlinear optical materials. 

Asher S, Chang S-Y, Tse A, Liu L, Pan G, Wu Z, Li P. Optically nonlinear crystalline colloidal self assembled submicron periodic structures for optical limiters. Material Research Society Symposium Proceedings 1995, 374, 305-310. 

In the fields of organometallic polymer see Polymer) chemistry , in which complexes may have particularly interesting physical properties (liquid crystallinity, optical nonlinearity see Nonlinear Optical Materials), etc.), or of molecular electronics , metal alkynyl complexes play a significant role. These areas have been the subject of recent reviews, thus only a brief overview of methods to prepare iron alkynes will be given here. Liu has also recently reviewed the cyclization chemistry of alkynyl organometaUics, including those of iron. ... 

Side-chain liquid-crystalline polymers with controlled molecular weights have been obtained by the polymerization of FM-25 with 1-22 (X = Br)/CuBr/ L-3 in the bulk at 100 °C, to examine the thermotropic transition as a function of the MWD.324 Second-order nonlinear optical materials with branched structure were prepared by the copper-catalyzed radical polymerization of FM-26 and FM-27 using hyperbranched poly[4-(chloromethyl)styrene] as a multifunctional initiator.325... 

As one of our central missions is to uncover the relation between microscopic and continuum perspectives, it is of interest to further examine the correspondence between kinematic notions such as the deformation gradient and conventional ideas from crystallography. One useful point of contact between these two sets of ideas is provided by the Cauchy-Bom rule. The idea here is that the rearrangement of a crystalline material by virtue of some deformation mapping may be interpreted via its effect on the Bravais lattice vectors themselves. In particular, the Cauchy-Bom mle asserts that if the Bravais lattice vectors before deformation are denoted by Ej, then the deformed Bravais lattice vectors are determined by e = FEj. As will become evident below, this mle can be used as the basis for determining the stored energy function W (F) associated with nonlinear deformations F. 

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