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This six month grant provided a continuation at Stanford University of AFOSR Grant No. F49620-96-1-0135, which ended 31 Mar 1999 at the University of California, San Diego (UCSD). During the period of this grant, accomplishments are of note. A major study of the effect of nonlinear chromophore energetic on the several speed of photorefractive polymers showed that rational design can improve the properties of these materials. Second, the entire laboratory moved from UCSD to Stanford University in July 1999. During this time, a major review article on photorefractive polymers for the Encyclopedia of Materials Science and Technology was completed (Pub. 171). Finally, in the new laboratories at Stanford, a first demonstration of fast image amplification with photorefractive polymers was completed.
Photorefractive polymer composites are an unusually sensitive class of photopolymers. Physics of Photorefraction in Polymers describes our current understanding of the physical processes that produce a photorefractive effect in key composite materials. Topics as diverse as charge generation, dispersive charge transport, charge compensation and trap
During the last two decades, the production of polymers and plastics has been increasing rapidly. In spite of developing new polymers and polymeric materials, only 40~60 are used commercially on a large scale. It has been estimated that half of the annual production of polymers is employed outdoors. The photochemical instability of most polymers limits their outdoor application as they are photodegraded quickly over periods from months to a few years. To the despair of technologists and consumers alike, photodegradation and environmental ageing of polymers occur much faster than can be expected from knowledge collected in laboratories. In order to improve polymer photostability there has been a very big effort during the last 30 years to understand the mechanisms involved in photodegradation and environmental ageing. This book represents the author's attempt, based on his 25 years' experience in research on photodegradation and photo stabilization, to collect and generalize a number of available data on the photodegradation of polymers. The space limitation and the tremendous number of publications in the past two decades have made a detailed presentation of all important results and data difficult. The author apologizes to those whose work has not been quoted or widely presented in this book. Because many published results are very often contradictory, it has been difficult to present a fully critical review of collected knowledge, without antagonizing authors. For that reason, all available theories, mechanisms and different suggestions have been presented together, and only practice can evaluate which of them are valid.
This report describes our effort in the past three years on synthesis and characterization of novel photorefractive polymer system. Two major systems were developed, one of which combined the ionic transition metal complexes and a conjugated polymer backbone bearing NLO chromophores to manifest large photorefractive effect. Another is a molecular material containing oligothiophene and a nonlinear optical (NLO) chromophore. A large net optical gain (>200/cm) at a zero electric field was observed in the metal containing system. In the molecular system, a net optical gain of 83/cm and a diffraction efficiency of nearly 40% were obtained in a film made from this molecule under an applied field of 706 kv/cm. A fast response time of for the grating formation, 42 ms under 616 kv/cm, was observed.
This book provides comprehensive, state-of-the art coverage of photorefractive organic compounds, a class of material with the ability to change their index of refraction upon illumination. The change is both dynamic and reversible. Dynamic because no external processing is required for the index modulation to be revealed, and reversible because the index change can be modified or suppressed by altering the illumination pattern. These properties make photorefractive materials very attractive candidates for many applications such as image restoration, correlation, beam conjugation, non-destructive testing, data storage, imaging through scattering media, holographic imaging and display. The field of photorefractive organic material is also closely related to organic photovoltaic and light emitting diode (OLED), which makes new discoveries in one field applicable to others.
The photorefractive effect is now firmly established as one of the highest-sensitivity nonlinear optical effects, making it an attractive choice for use in many optical holographic processing applications. As with all technologies based on advanced materials, the rate of progress in the development of photorefractive applications has been principally limited by the rate at which breakthroughs in materials science have supplied better photorefractive materials. The last ten years have seen an upsurge of interest in photorefractive applications because of several advances in the synthesis and growth of new and sensitive materials. This book is a collection of many of the most important recent developments in photorefractive effects and materials. The introductory chapter, which provides the necessary tools for understanding a wide variety of photorefractive phenomena, is followed by seven contributed chapters that offer views of the state-of-the-art in several different material systems. The second chapter represents the most detailed study to date on the growth and photorefractive performance of BaTi03, one of the most important photorefractive ferroelectrlcs. The third chapter describes the process of permanently fixing holographic gratings in ferroelectrics, important for volumetric data storage with ultra-high data densities. The fourth chapter describes the discovery and theory of photorefractive spatial solitons. Photorefractive polymers are an exciting new class of photo refractive materials, described in the fifth chapter. Polymers have many advantages, primarily related to fabrication, that could promise a breakthrough to the marketplace because of ease and low-cost of manufacturing.
Photorefractive materials combine photoconductive and electro-optic properties: light affects their electrical conductivity; their optical properties (refractive index, etc.) are affected by applied electric fields. The aim of this book is to cover the vast range of phenomena occurring in Photorefractive Materials. For Physicists it is part of the fashionable subject of Nonlinear Optics. Engineers tend to place it as part of optoelectronics promising a variety of new devices. This book summarizes the results of 28 years of research in a manner that would appeal both to the beginner (a graduate student who has just entered the field) and to the expert (who might have done research on some aspect of the subject for a decade or more). It is in three parts. Part I serves as an introduction with emphasis on physical principles and simple mathematical models. Part II is a comprehensive account of all the major advances. Its main merit is the organization of the material accompanied by a detailed list of references. Part III is concerned with the enormous range of potential applications.
Optical Properties of Functional Polymers and Nano Engineering Applications provides a basic introduction to the optical properties of polymers, as well as a systematic overview of the latest developments in their nano engineering applications. Covering an increasingly important class of materials relevant not only in academic research but also in industry, this comprehensive text: Considers the advantages of the liquid gradient refractive index (L-GRIN) lenses over the conventional solid lenses Explores the electrochemistry of photorefractive polymers, the molecular structure of commonly used polymers, and various 3D holographic displays Discusses gene detection using the optical properties of conjugated polymers Highlights the physics of fluorescence in photoluminescent polymers, and energy and electron transfer mechanisms Introduces conventional polymer ion sensors based on the optical sensors of conjugated polymers prepared by click chemistry reactions Explains colorimetric visual detection of ions by donor–acceptor chromophores Describes optical sensors based on fluorescent polymers and for the detection of explosives and metal ion analytes Addresses holographic polymer-dispersed liquid crystal technology, its optical setups, and its applications in organic lasers Presents cutting-edge research on electrochromic devices, along with new concepts, prototypes, commercial products, and future prospects Demonstrates new techniques for creating nanoscale morphologies through self-assembly, which affect the optical properties of the functional polymers Optical Properties of Functional Polymers and Nano Engineering Applications emphasizes the importance of nano engineering in improving the fundamental optical properties of the functional polymers, elaborating on high-level research while thoroughly explaining the underlying principles.
This paper describes the properties of a new class of materials exhibiting the photorefractive effect, doped nonlinear organic polymers. Photorefraction (at 647.1 nm) was established by a combination of hologram erasability, correlation with photoconductivity and electro-optic response, and enhancement by external fields in numerous samples of two nonlinear epoxy materials doped with hole transport agents based on p-diethylaminobenzaldehyde- diphenyl hydrazone (DEH). Diffraction efficiencies up to 0.1% were observed at bias fields near 100 kV/cm. A useful property of these materials is that poling of the nonlinear chromophores is partially reversible, permitting partial control of the grating readout independent of the space-charge field formed. The polarization anisotropy of grating readout is consistent with the photorefractive mechanism.