Nonlinear Optical Properties of Hierarchical Systems
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NONLINEAR OPTICAL PROPERTIES OF HIERARCHICAL SYSTEMS
PARAS N. PRASAD Photonics Research Laboratory, Department of Chemistry, State University of New York at Buffalo, Buffalo, NY 14214
ABSTRACT Nonlinear optical processes provide many of the functions needed for Photonics Technology. Molecular materials are hierarchical systems in which the structure can be controlled from the angstrom level to macroscopic scale to optimize the nonlinear optical properties. In this article basic concepts of nonlinear optics and photonics are reviewed. Multifunctional molecular hierarchical systems are discussed which involves heterostructure design at molecular and bulk levels. For optimization of nonlinear response at the molecular level, guidance from theoretical modeling and study of sequentially built and systematically derivatized structures has proven to be useful. The use of Langmuir-Blodgett film approach to control the order and conformation with monolayer resolution is discussed. Examples of our approach to optimize the response at the bulk level involve the use of orientation control by electric field poling and use of composite heterostructures. An important advancement in heterostructure design is the use of sol-gel processing to make organic-inorganic composites which have successfully exhibited electro-optic modulation and femtosecond Kerr gate operations. Finally, novel photorefractive molecular materials are discussed.
PHOTONICS AND NONLINEAR OPTICS Photonics is the analog of electronics where photons instead of electrons are used to carry information. Applications range from fiber-optic communication to optical computing and other optical processing of information and images. In addition, the technology of photonics can also be used for new applications not provided by electronics. One example is sensor protection (or even eye protection) against laser threats. To emphasize the importance of photonics, other terms such as light wave technology and optical circuitry have also been used. Nonlinear optical processes provide important functions of frequency conversion (like frequency-doubling to increase the density of data storage), light control by electric field (electro-optic effect) and even all optical processing such as light control by light (1]. Utilizing these manifestations of optical nonlinearities, one can build devices such as frequency converters, light modulators, all optical switches, optical logic, optical memory storage, and optical limiters. The technology of photonics with devices using nonlinear optical processes offers many advantages; among them the most important ones are: (i) gain in speed of signal processing, (ii) three dimensional connectivity (optical neural network) to produce smaller integrated optical chips, (iii) no electrical and magnetic interference, and (iv) compatibility with fiber-optics link. Nonlinear optical processes occur when a medium is subject to an intense light pulse such as that from a high peak power laser [1]. The strong oscillating electric field of the laser cre
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