Crystals second-order nonlinearity

Equation (2) is identified as a second-order, nonlinear differential equation once, the curvature is expressed in terms of a shape function of the melt/crystal interface. The mean curvature for the Monge representation y = h(x,t) is... 

Electrooptic displays, liquid crystal polymers in, 75 110 Electrooptic effect, 74 675 Electrooptic modulation, second-order nonlinear optical materials for, 77 444... 

In this paper, an overview of the origin of second-order nonlinear optical processes in molecular and thin film materials is presented. The tutorial begins with a discussion of the basic physical description of second-order nonlinear optical processes. Simple models are used to describe molecular responses and propagation characteristics of polarization and field components. A brief discussion of quantum mechanical approaches is followed by a discussion of the 2-level model and some structure property relationships are illustrated. The relationships between microscopic and macroscopic nonlinearities in crystals, polymers, and molecular assemblies are discussed. Finally, several of the more common experimental methods for determining nonlinear optical coefficients are reviewed. 

It is evident that two hydrogen bonds between adjacent molecules and the chirality of molecule contribute to one dimensional molecular alignment in spite of the strong dipole-dipole interactions and that -conjugated system of DAD molecule extend from amino groups to cyclobutenedione ring enhance second order nonlinearity of DAD molecular crystal. 

The basic structural units responsible for the second order nonlinear optical susceptibility in most oxide crystals are the acentric anionic groups. (4,6) The... 

The EO effect is a second-order nonlinear optical (NLO) effect. Only non-centrosymmetrical materials exhibit second-order NLO effects. This non-centrosymmetry is a condition, both at the macroscopic level of the bulk arrangement of the material and at the microscopic level of the individual molecule. All electro-optic modulators that are presently used by telecom operators are ferro-electric inorganic crystals. The optical nonlinearity in these materials is to a large fraction caused by the nuclear displacement in the applied electric field, and to a smaller fraction by the movement of the electrons. This limits the bandwidth of the modulator. The nonlinear response of organic materials is purely electronic and, therefore, inherently faster. 

Recently, a second-order nonlinear photonic crystal has been realized.38 In this nonlinear optical bandgap material, there is a periodicity in the nonlinear optical properties of the engineered material. With this definition, a periodically poled second-order nonlinear optical material could be called a nonlinear photonic crystal. However, its linear optical properties do not show a periodicity, except for the (small and useless for bireffingent phase-matching) poling-induced birefringence. Here, the material is the same in the complete structure. It is only periodically made into a non-centrosymmetric structure for second-order nonlinear and phase-matching... 

Typical values of the second-order nonlinear coefficient d for dielectric crystals, semiconductors, and organic materials used in photonics applications lie in the range d = 10 24 to 10 - (mks units, As/V2). Typical values of the third-order nonlinear coefficient x(3> for glasses, crystals, semiconductors, semiconductor-doped glasses, and organic materials of interest in photonics are x -3 = 10 34 to 10 29 (mks units). 

Reviewed in Zyss J, Chemla DS (1987) Quadratic nonlinear optics and optimization of the second-order nonlinear optical response of molecular crystals. In Chemla DS, Zyss J (eds) Nonlinear and optical properties of organic molecules and crystals. Academic Press, Orlando, p 23... 

J. Zyss and D.S. Chemla, Quadratic Nonlinear Optics and Optimization of Second-Order Nonlinear Optical Response of Molecular Crystals, Eds. D.S. Chemla and J. Zyss, Academic Press, Orlando, FL, 1987, Vol. 1, pp. 23-191. 

The principal structural requirement for second order nonlinear effects in assemblies of molecules is the lack of a centre of symmetry, and considerable efforts have been expended in trying to induce potentially useful molecular entities to crystallize in non-centrosymmetric or polar crystals (Curtin and Paul 1981 Liter et al. 1991). As demonstrated below, this is a necessary, but not sufficient condition for obtaining nonlinear effects. True to form, the variety of crystallization experiments has led to a number of polymorphic structures, and to information about the relationship between the properties of these materials and their structures, as well as useful guidelines for attempting to obtain the desired non-centrosymmetric crystal structures. 

Moreover, the isolation of self-assembled LiNbOj powders using this route has added credibility to the methodology they were otherwise prepared by templating colloidal crystals of polyelectrolyte-coated spheres. The interest in LiNb03 inverse opals stems from the fact that they have a constant refractive index, but a spatially periodic second-order nonlinear susceptibility. Such nonlinear periodic structures allow for efficient qnasi-phase-matched second-order harmonic generation, which conld find applications where simultaneous conversion of multiple wavelengths is reqnired. Thns, in this chapter we will focus our... 

---