Peter Günter – författare

In this second volume of the book series devoted to photorefractive effects we focus on the most recent developments in the field of photorefractive materials and we highlight the parameters which govern the photoinduced nonlinearity. The availability of materials having the required properties is of major importance for further development of this field, and there are many parameters which have to be considered in the figure of merit of a photorefractive material. As an example, it concerns in priority, the recording slope of the dynamic hologram and the saturation value of the index modulation which are specific characteristics of a given material. However, other features like spectral sensitivity range, dark storage time, material stability and power handling capabilities are also critical parameters to consider when using the crystal for advanced applications in laser photonics. There are a large diversity of potential materials which exhibit interesting photorefractive properties, like ferroelectric or non ferroelectric electro-optic crystals, semi insulating semiconductors or electro-optic polymers. If the basic mechanisms for space charge recording are well established, it is now required to have a very precise and extended knowledge of the physics of the charge transfer and related mechanisms which arises in doped materials. Also, we must know the material response for different conditions of hologram recording wavelength, laser intensity, continuous or pulsed regime. These research achievements on the physics of the photorefractive materials is of great importance in order to optimize or to tailor material properties. The main purpose of this second volume is to highlight the advances in material research but also including crystal growing conditions or material preparations and their impact on photorefractive performances. Following this objective, the reader will find in this book very detailed analysis on the material physics : investigations ofdefects in crystal, growing of stochiometric LiNbO3 or LiTaO3, a new crystal Sn2P2S6 for the near infrared, Quantum Well semiconductor structures and Sillenites.  Beside the conventional electro-optic crystals, the volume also deals with organic photorefractive materials. Large progress have been made in the field recently in term of material sensitivity and efficiency under applied electric field. It is undoubtly a class of material of growing interest. We are confident that new advances will be done on the chemistry and on the synthesis of the polymers for a better control and optimization of the photorefractive properties. A closely related field is the photorefractive effect in liquid crystals materials, which exhibit attractive perspectives due to their large photoinduced index modulation. We also outline in this volume two other contributions which have an important impact for applications : the mechanisms of permanent photoinduced gratings in Silica-glass fibers used as wavelength selective Bragg filters and the growing of materials like LiNbO3 which have to be highly resistant to photorefractive damage for electro-optic and nonlinear optic applications. This volume gives an in depth review of the present understanding of the fundamental origins of the effect in a variety of materials. All the materials considered in this volume will play a significant role in the development of applications such as presented in the third volume of this serie. The contribution of the material is determinant for new progress in the field of photorefractive nonlinear optics. It is therefore most important to stimulate significant efforts of research on the basic physical phenomena in different materials. These research achievements may contribute to the discovery of new class of photorefractive material or will permit to optimize the performances of existing materials.

This is the third and final volume of a three volumes book series 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 unexpected effects have been discovered, theoretical models developed, known effects could be finally explained and novel applications had been 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 out of print since long time.

The first volume is devoted to the description of the basic effects leading to photoinduced refractive index changes in electro-optical materials. In the second volume the status of the most recent developments in the field of photorefractive materials is reviewed and the parameters, which govern the photorefractive nonlinearity are highlighted.

This third volume deals with the applications of the photorefractive effects and of materials. Starting about 35 years ago the attractivity of the photorefractive effect for data storage, for optical metrology, optical signal processing and nonlinear optical applications has been recognized. One of the main reasons for this is the large nonlinearity or refractive index change, which can be induced by low light intensities by using the photoinduced space-charge fields in electro-optical materials. Many new concepts have been demonstrated in the laboratories over all these years. Several of these concepts have been proved useful also in other areas of nonlinear optics. Particularly interesting was the observation of a large energy from pump beams to the signal beam in two- and fourwave mixing experiments. This effects lead to coherent amplification of a waveform covering spatial information and to self-pumped optical phase conjugation with applications in the area of wavefront correction of self-induced optical resonators.

In this third volume a series of applications of photorefractive nonlinear optics and of optical data storage are presented in several chapters.

This and the other two volumes on photorefractive effects, materials and applications have been prepared mainly for researchers in the field, but also for physics, engineering and materials science students. Several chapters contain sufficient introductory material for those not so familiar with the topic to obtain a thorough understanding of the photorefractive effect. We hope that for researchers active in the field these books should provide a useful reference source for their work.