Solids, second-order nonlinear optics

Second-Order Nonlinear Optical Processes in Molecules and Solids... 

This has always been held to be true. However, in a limited number of examples, centric molecules do give rise to second-order nonlinear optical effects in the bulk. This is attributed to solid-state effects. See, for example. Ref (12). 

D. J. Williams, in Materials for Nonlinear Optics—Chemical Perspectives, S. R. Marder, J. E. Sohn, and G. D. Stucky, Eds., ACS Symposium Series 455, American Chemical Society, Washington, DC, 1991, pp. 31-49. Second-Order Nonlinear Optical Processes in Molecules and Solids. 

Cui, Y., Qian, G., Chen, L., Wang, Z., and Wang, M. 2008. Second-order nonlinear optical properties of cross-linked silica films prepared through sol-gel process. Thin Solid Films 516 5483-5487. 

Khougaz K, Clas S-D (2000) Crystalhzation inhibition in solid dispersions of MK-0591 and poly(vinylpyrrolidone) polymers. J Pharm Sci 89 1325-1334 Kissick DJ, Wanapun D, Simpson GJ (2011) Second-order nonlinear optical imaging of chiral crystals. Annu Rev Anal Chem (Palo Alto, Cahf.) 4 419-437 Klama F (2010) NMR-studies of multi component solids. M. Sc. Dissertation, University of East Anglia, p 186... 

Most theoretical discussions for molecules concentrate on calculations of second-order nonlinear optical properties. These results can be used equally well for the design of either molecules or molecular fragments. The latter are intended for inclusion in polymers as either a solid solution or side-chains. These are discussed in detail in section 4.3, together with systems in which a crystalline phase is dispersed in a polymer matrix. In molecularly dispersed systems the incorporation and orientation of an active species in a polymer obviates the need for a non-centrosymmetric crystal structure but does require the imposition of a polar state on the polymer (e.g. with an applied electric field). Thus molecular species that as crystals are not useful as second-order nlo materials (because they adopt a centrosymmetric structure) may be applicable in a polymeric system. Though it has received less attention in the past, considerable effort has recently been devoted to theoretical studies of... 

Our interest in bowlic liquid crystals has arisen from the proposal that bowl shaped molecules may exhibit polar (noncentrosymmetric) organization in the liquid crystalline phases [4, 8, 9]. Indeed bowlic liquid crystals are natural noncentrosymmetric building blocks since a head-to-tail organization maximizes the interactions between bowlic cores. New methodologies for the creation of noncentrosymmetric structures in molecular solids and liquids are critical to the development of new materials with ferroelectric and second order nonlinear optical (NLO) properties [14, 15]. Liquid crystalline methods are particularly attractive since liquid crystalline materials are easily deposited for device construction and are readily aligned. 

The interfaces in general, and particularly with solid substrates break the head-to-tail symmetry of a liquid crystal phase and induce polar orientational order. The symmetry is reduced to the conical group Coov The latter allows a finite value of the second-order nonlinear susceptibility X2 responsible for the second optical harmonic generation [11]. This phenomenon has been observed in experiments on generation of the second harmonic in a ultrathin nematic layers on a solid substrate as shown in Fig. 10.9. 

In the field of solid state physics, one of the most investigated materials is ferroelectric, which has important applications as memory switching [1-4], nonlinear optical communications [5], non-volatile memory devices [6, 7], and many others [8, 9]. Ferroelectrics have also emerged as important materials as (a) piezoelectric transducers, (b) pyroelectric detectors, (c) surface acoustic wave (SAW) devices, and (d) four-phase mixing doublers. Both lithium tantalate and lithium niobate appear to be promising candidates as the key photonic materials for a variety of devices (a) optical parametric oscillators, (b) nonlinear frequency converters, (c) second-order norrlinear optical material, and (d) holography, etc. Many of such devices include important nano-devices [9-11],... 

Recently there has been a great deal of interest in nonlinear phenomena, both from a fundamental point of view, and for the development of new nonlinear optical and optoelectronic devices. Even in the optical case, the nonlinearity is usually engendered by a solid or molecular medium whose properties are typically determined by nonlinear response of an interacting many-electron system. To be able to predict these response properties we need an efficient description of exchange and correlation phenomena in many-electron systems which are not necessarily near to equilibrium. The objective of this chapter is to develop the basic formalism of time-dependent nonlinear response within density functional theory, i.e., the calculation of the higher-order terms of the functional Taylor expansion Eq. (143). In the following this will be done explicitly for the second- and third-order terms... 

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