Nonlinear optics fundamental concepts

This review has covered many of the essential features of the physical chemistry of nanocrystals. Rather than provide a detailed description of the latest and most detailed results concerning this broad class of materials, we have instead outlined the fundamental concepts which serve as departure points for the most recent research. This necessarily limited us to a discussion of topics that have a long history in the community, leaving out some of the new and emerging areas, most notably nonlinear optical studies [152] and magnetic nanocrystals [227]. Also, the... 

To introduce the subject matter of this volume, the fundamental concepts of nonlinear optics and their relationship to chemical structures are briefly summarized. In the dipolar approximation, the polarization induced in an atom or molecule by an external field E can be written as... 

The applicable fundamental concepts of nonlinear integrated optics for SHG were outlined decades ago and can be found in a number of review papers [6-8]. The basic theory as applied to organic materials and polymers is of course unchanged from that for dielectric materials and these papers are still very useful. Some twenty plus years ago, nonlinear integrated optical experiments started to be conducted, but mostly on inorganics and crystals. The specific field of amorphous and semi-ordered organics came when the chemical engineering of nonlinear chromophores was developed. 

Many significant fundamental concepts and practical applications have developed since the publication of the best-selling second edition of the Handbook of Conducting Polymers. Now divided into two books, the third edition continues to retain the excellent expertise of the editors and world-renowned contributors while providing superior coverage of the recent advances in polymer processing and applications, particularly in conductivity, nonlinear optics, and light emission. 

Although nonlinear optical properties of materials are known for more than a century, the relevance of organics and polymers in this fascinating area of research originates from a more recent development To introduce the subject of this paragraph, the fundamental concepts of nonlinear optics and their relation to chemical structure are briefly summarized. 

Based on the fundamental dipole moment concepts of mesomeric moment and interaction moment, models to explain the enhanced optical nonlinearities of polarized conjugated molecules have been devised. The equivalent internal field (EIF) model of Oudar and Chemla relates the j8 of a molecule to an equivalent electric field ER due to substituent R which biases the hyperpolarizabilities (28). In the case of donor-acceptor systems anomalously large nonlinearities result as a consequence of contributions from intramolecular charge-transfer interaction (related to /xjnt) and expressions to quantify this contribution have been obtained (29). Related treatments dealing with this problem have appeared one due to Levine and Bethea bearing directly on the EIF model (30), another due to Levine using spectroscopically derived substituent perturbations rather than dipole moment based data (31.) and yet another more empirical treatment by Dulcic and Sauteret involving reinforcement of substituent effects (32). 

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