This is the first of two volumes that review, for the first time, all major aspects of photorefractive effects and their applications. Photorefractive effects in electro-optic crystals are based on optically induced space-charge fields which ultimately alter the refractive indices by the electro-optic Pockels effect. The fundamental phenomena leading to photoinduced changes of refractive index, the materials requirements and experimental results on a variety of photorefractive materials are discussed and the most recent theoretical models describing these phenomena are presented. Interest in photorefractive materials has increased in recent years mainly because of their potential for nonlinear optical devices and for optical signals processing applications. Most of these applications are reviewed in the second volume devoted to this topic. The contributions to these two volumes are written by experts on each topic and are intended for scientists and engineers active in the field and for researchers and graduate students entering the field. Over 300 references to original papers on photorefractive and associated phenomena are cited.

The invention ofthe laser 25years ago resulted in powerfullight sources which led to the observation of unexpected and striking phenomena. New fields of science such as holography and nonlinear optics developed constituting the basis of this volume. The classical principle of linear superposition of light wavesdoes not hold anymore. Two laser beams crossing in a suitable material may produce a set of new beams with different directions and frequencies. The interaction of light waves can be understood by considering the optical grating structures which develop in the overlap region. The optical properties of matter become spatially modulated in the interference region of two light waves. Permanent holographic gratings have been produced in this way by photographic processes for many years. In contrast, dynamic or transient gratings disappear after the inducing light source, usually a laser, has been switched off. The grating amplitude is controlled by the light intensity. Dynamic gratings have been induced in a large number ofsolids, liquids, and gases, and are detected by diffraction, 'forced light scattering' of a third probing beam, or by self-diffraction of the light waves inducing the grating. The combined interference and diffraction effect corresponds to four-wave mixing (FWM) in the language of nonlinear optics. The process is called degenerate ifthe frequenciesofthe three incident wavesand the scattered wave are equal. Degenerate four-wave mixing (DFWM) is a simple method to achieve phase conjugation, i.e. to generate a wave which propagates time reversed with respect to an incident wave.

This is the second of two volumes that review, for the first time, all major aspects of photorefractive effects and their applications. Photorefractive effects in electro-optic crystals are based on optically induced space-charge fields which ultimately alter the refractive indices by the electro-optic Pockels effect. The fundamental phenomena leading to photoinduced changes of refractive index, the materials requirements and experimental results on a variety of photorefractive materials are discussed and the most recent theoretical models describing these phenomena are presented. Interest in photorefractive materials has increased in recent years mainly because of their potential for nonlinear optical devices and for optical signals processing applications. Most of these applications are reviewed in this volume. The contributions to the two volumes are written by experts on each topic and are intended for scientists and engineers active in the field and for researchers and graduate students entering the field. Over 300 references to original papers on photorefractive and associated phenomena are cited. Volume 1 appeared as Volume 61 of "Topics in Applied Physics."

Describing progress achieved in the field of nonlinear optics and nonlinear optical materials, the Handbook treats selected topics such as photorefractive materials, third-order nonlinear optical materials and organic nonlinear optical crystals, as well as electro-optic polymers. Applications of photorefractive materials in optical memories, optical processing, and guided-wave nonlinear optics in hotorefractive waveguides are described. As light will play a more and more dominant role as an information carrier, the review of existing and new materials given here makes this a keystone book in the field.

This volume is based on lectures and contributed papers presented at the Eleventh Course of the International School of Materials Science and Tech nology that was held in Erice, Sicily, Italy at the Ettore Majorana Center for Scientific Culture during the period 6-17 July 1986. The subject of the course was "Electro-optic and Photorefractive Materials: Applications in Sig nal Processing and Phase Conjugation" . The fields of electro-optics and photorefraction have developed rapidly since the invention of lasers just over twenty-five years ago. The possibil of altering the optical properties of a material by electric fields or by ity optical waves is of great importance for both pure science and for practical applications such as optical signal processing, telecommunications and opti cal display devices. These effects allow us to manipulate (modulate, deflect) and process a given light wave. Modulation, deflection and processing of light waves by means of the electro-optic effect is of fundamental importance in fiber optic telecommuniC1. tions and sensor systems w here the light signals can be processed prior or subsequent to transmission through the fibers. Thin film electro-optic materials with suitable electrode arrays on. the surface of the wave-guiding structures result in a technology often referred to as inte grated optics. In principle, integrated optics devices allow miniaturization and integration of many operations onto a single chip. The photorefractive effect, defined as a photo-induced change of the in dices of refraction, was the other topic treated in this course."

This second volume of the series on photorefractive effects focuses on the most recent developments in the field and highlights the parameters which govern the photoinduced nonlinearity. Besides reviewing conventional electro-optic crystals, this book deals with organic photorefractive materials, giving an in-depth assessment of the present understanding of the effect in a variety of materials. The materials considered in this volume will play a significant role in the development of applications such as presented in the third volume.

This is the first volume of a set of three within the Springer Series in Optical Sciences, and is devoted to photorefractive effects, photorefractive materials, and their applications. Since the publication of our first two Springer books on Photorefractive Materials and Their Applications (Topics in Applied Physics, Vols. 61 and 62) almost 20 years ago, a lot of research has been done in this area. New and often expected effects have been discovered, theoretical models developed, known effects finally explained, and novel applications proposed. We believe that the field has now reached a high level of maturity, even if research continues in all areas mentioned above and with new discoveries arriving quite regularly. We therefore have decided to invite some of the top experts in the field to put together the state of the art in their respective fields. This after we had been encouraged to do so for more than ten years by the publisher, due to the fact that the former volumes were long out of print.

This is the final volume of a series devoted to photorefractive effects, photorefractive materials and their applications. Since publication of the first two volumes almost 20 years ago, new and often unexpected effects have been discovered. Theoretical models have been developed, known effects can be finally explained and novel applications have been proposed. For this volume, the editors have invited top experts to reflect on the maturity of the field, assessing progress so far, and predicting avenues of future development. In addition, a series of applications of photorefractive nonlinear optics and of optical data storage are presented in several chapters.