Nonlinear Optical Property Basics

The major trends in ferroelectric photonic and electronic devices are based on development of materials with nanoscale features. Piezoelectric, electrooptic, nonlinear optical properties of fe are largely determined by the arrangement of ferroelectric domains. A promising way is a modification of these basic properties by means of tailoring nanodomain and refractive index superlattices. 

Numerous investigations into the nonlinear optical properties of certain organic and polymeric materials have shown that these materials possess the largest observed optical non-linearities. These nonlinearities, whose physical mechanisms were elucidated by basic... 

In this chapter we have introduced the basic elements of the theory of nonlinear optical properties. Emphasis has been laid on the basic physical processes involved and how these processes are reflected in the basic formulas derived from time-dependent perturbation theory. We have also briefly outlined the strategies for developing efficient computational methods for the calculation of linear and nonlinear optical properties. A brief discussion of the contributions to the nonlinear optical properties arising from the nuclear motions, as well as the connection between the... 

In this tutorial on the basic ideas and modern methods of computational chemistry used for the prediction of nonlinear optical properties, the focus is on the most common computational techniques applicable to molecules. The chapter is not meant to be an exhaustive review of nonlinear optical theories, nor is it a compendium of results. Although much is omitted from this chapter, there exist several earlier reviews on the general subject of nonlinear optics that help form a broad foundation for this work. " The material in this chapter will, hopefully, be of value to readers who are interested in learning enough about computational nonlinear optical methods to discern the differences between high and low quality results and limitations of modern methodologies, and to readers who would like to join the effort to improve the calculations. 

The finite field method is the simplest method for obtaining nonlinear optical properties of molecules. This method was first used by Cohen and Roothaan to calculate atomic polarizabilities at the Hartree-Foclc level. The basic idea is to truncate the expansion of the energy (Eq. [6]) and solve for the desired coefficients by numerical differentiation. For example, if the expression is truncated after the quadratic term, the result is E(P) = E[0) — — iot yF,Fy. 

Linear optical properties such as linear polarizabilities can be calculated relying on the theory mentioned above. For nonlinear optical properties there are several approximate methods available too. Some of the most basic ones are given below in a qualitative manner. For further reading a number of excellent books on the subject is suggested (8-10). 

In this chapter we will shortly summarize the nonlinear optical properties of macromolecular systems and some of the main experimental techniques for their optical characterization. Some basic optoelectronic patterns will be reported in order to give a brief account of the advances in the realization of active waveguide systems and telecommunication devices based on organic materials. The main optoelectronic devices based on nonlinear optical properties of chromophores in polymeric and hybrid matrices will be illustrated. In particular Mach-Zehnder modulators, microring resonators, switches and wavelength filters will be reviewed. 

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. 

Three basic questions must be answered to ensure success in the search for an optimized nonlinear crystal for a particular application What are the most important optical properties which determine the crystal s figure of merit for the intended application What is the best methodology for characterizing those optical properties so that materials of interest can be identified efficiently Where in "materials space" can crystals with such properties be found with the highest probability Answers to these questions will be discussed in the context of a program to find improved frequency conversion crystals for high power lasers. 

Besides other intriguing properties, such as inherent planar chirality, metallocenes are of interest due to their considerable Lewis basicity. Their direct or conjugative attachment to a polymer chain should enhance the electron density along the main chain and therefore lower the HOMO-LUMO band gap. In addition, organometallic compounds and metallocene-based monomers and polymers represent interesting potential nonlinear optical materials, useful for frequency doubling, modulation, and switching, for three reasons ... 

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... 

A continuous research work on membrane properties and fundamental aspects of transport phenomena in the various membrane operations is important for the fumre of membrane science and technology. There is a need for both basic and applied research to develop new membranes with improved properties and new membrane processes. These research efforts must take into account the studies done in other areas such as supramolecular chemistry, molecular imprints materials, nanotechnology, nonlinear optics, studies on biological membranes and biological phenomena, etc. 

Photochromic materials based on different classes of spiropyrans (SPs) are widely used in various fields of science and technology, such as in the production of light filters regulating luminous fluxes, as photochromic organic media for processing optical information, for photochromic optics, and in the production of nonlinear optical materials. In recent years, the study of new SPs has been conducted mainly in two directions, namely, the search for new classes of SPs and structural modification of the known systems to improve their basic characteristics (quantum yield of photoconversion, the stability of the photoisomer produced, the number of cycles of operations). Only a profound comprehension of mechanisms of photoinitiated rupture of the Cspiro—O bond, structural isomerization, ways of stabilizing the photoisomer, routes of its breakdown, and influence of the structure of SPs on their properties can provide the basis for purposeful research in this area. Despite the vast number of investigations in this area, the mechanisms of the photochromic conversion of SPs and the influence of structural features on their photochemical properties are not well understood. This complicates the search for and synthesis of new SP classes. 

In the previous sections the basic nonlinear optical interactions have been described, along with some of their properties. In the following sections we shall describe applications of the various nonlinear interactions. Some applications have already been noted in the description given for certain effects. Here we shall describe applications that can be made with a wide variety of interactions. 

At the same time, the inherent differences in the electronic structure between first-row bonding and mixed first- and second-row bonding present in the phosphonitrilic system now become the controlling factor for the nonlinear yield. Basically, both the characteristics of the linear optical properties and the large degree of charge localization in these systems limit the nonlinear yield in these systems. 

Second-harmonic generation for nonlinear optics, ferroelectricity, and piezoelectricity are all properties that are dependent on the pre.sence, magnitude, and orientation of bulk polarity in crystals and films. Therefore, the issue of how to design a polar solid from basic principles remains a challenge that has immense potential relevance to materials science. Obviously, a polar solid is guaranteed if a pure enantiomer is used as a component of a compound. However, the presence of polarity does not in any way imply that optimal packing will occur and, further-... 

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