We have studied the basic spectroscopy, kinetics and nonlinear optical properties of a set of power limiting materials, which include six metallobenzoporphyrins and ten donor-acceptor azulenic molecules. These compounds are known to have highly polarizable it-electrons, and therefore are expected to have nonlinear coefficients suitable for utilization in optical limiting devices. In order to diagnose the optical limiting properties of the materials, we developed new two-dimensional Z-scan technique. This technique allows us to measure separately real and imaginary parts of the third order nonlinear susceptibility X(3) of the materials, using arbitrarily beam shaped laser pulse and arbitrary sample thickness. In addition, the beam profile evolution anywhere inside the optical limiting material can be extracted accurately using 2D Z-scan technique. We have tested this technique using Gaussian and non-Gaussian special beam distributions, thin and thick samples, and applied it to the molecules studied. Some of the molecules showed high nonlinear absorption and nonlinear refraction at the wavelength of the experiment 527 nm.

Recent developments in organic nonlinear optical materials for application to eye and sensor protection are reviewed. This compendium includes a brief discussion of the functioning of the eye, delineation of some of the important eye protection parameters and an introduction to the origin of nonlinear optical effects and how they are measured. Specific examples of proposed or prototyped protection devices are also presented. A compilation of noteworthy organic third-order nonlinear optical materials is included as an appendix. Lasers are playing an important and increasing role in modern society. Their present uses range from compact disc players to optical data-storage and communication systems. Because of this wide-spread use, the continuing expansion of lasers into other arenas and the low damage thresholds of human eyes and electro-optic sensors, there is increasing concern about eye and sensor protection from laser irradiation.

The goal of this research project is to develop novel optical materials and related structures with superior properties for use in nonlinear optics. This work is motivated by the need for high quality materials with large nonlinear coefficients for use in nonlinear and photonics devices and by the realization that new structures developed in recent years provide the possibility for new types of nonlinear optical devices and interactions. Devices that could benefit from these new and improved materials include eye/sensor protect ion devices, optical switches, and phase conjugating aberration correction devices.

The field of nonlinear optics developed gradually with the invention of lasers. After the discovery of second-harmonic generation in quartz, many other interesting nonlinear optical processes were rapidly discovered. Simultaneously theoretical programmes for the understanding of nonlinear optical phenomena were stimulated in accordance to develop structure-property relationships. In the beginning, research advances were made on inorganic ferroelectric materials followed by semiconductors. In the 1970's, the importance of organic materials was realised because of their nonlinear optical responses, fast optical response, high laser damage thresholds, architectural flexibility, and ease of fabrication. At present materials can be classified into three categories - inorganic ferroelectrics, semiconductors, and organic materials. Advances have also been made in quantum chemistry approaches to investigate nonlinear optical susceptibilities and in the development of novel nonlinear optical devices. Generally, inorganic and organic nonlinear optical materials and their related optical processes are reported in separate meetings. This book collects for the first time papers covering the recent developments and areas of present research in the field of nonlinear optical materials.

Nonlinear optical materials play a pivotal role in the future evolution of nonlinear optics in general and its impact in technology and industrial applications in particular. The progress in nonlinear optics has been tremendous since the first demonstration of an all-optical nonlinear effect in the early sixties, but until recently the main visible emphasis was on the physical aspects of the nonlinear radiation matter interaction. In the last decade, however, this effort has also brought its fruits in applied aspects of nonlinear optics. This can be essentially traced to the improvement of the performances of the nonlinear optical materials. Our understanding of the nonlinear polarization mechanisms and their relation to the structural characteristics of the materials has been considerably improved. In addition, the new development of techniques for the fabrication and growth of artificial materials has dramatically contributed to this evolution. The goal is to find and develop materials presenting large nonlinearities and satisfying at the same time all the technological requirements for applications such as wide transparency range, fast response, high damage threshold but also processability, adaptability and interfacing with other materials. Improvements, besides rendering possible the implementation of nonlinear effects in devices, open the way to the study of new nonlinear optical effects and the introduction of new concepts. This book describes new concepts which are emerging in the field of nonlinear optical materials, concentrating the attention on materials which seem more promising for applications in the technology of information transmission and processing.

It was the 50s and life was simple, until September 25, 1954. That was the night that would be etched in the memory of the citizens of Stanfield, Massachusetts. The Chief of Police described the brutal savagery of the double homicide as "the most atrocious crime in the history of the city." A fourteen-year-old girl, and the four-year-old boy in her care were murdered at the hands of a deranged, depraved killer. A Thread of Evidence places the reader at the scene of the crime, an eye witness to the senseless stabbing of two innocent children. With a piece of crochet thread as their only clue, the entire police department, lead by detectives Steven Logan and Raymond Gage, scour the city in search of a maniacal savage. When all tips and leads have been exhausted, they review all evidence. They come back to the thread. The only real evidence. With tenacity and perseverance of Logan and Gage the killer is apprehended. The reader experiences the twists and turns of the investigation, and ultimately occupies a reserved seat in the Superior Court as the trial proceedings commence. A Thread of Evidence has been written as fiction, but inspired by an actual event. Fifty years later, it remains etched in the minds of all who had lived in the area. The author has researched court records, newspapers, interviewed neighbors, police and has drawn on personal recollections of the crime. The story has been recounted over and over and to this day, it continues to be discussed. A Thread of Evidence is a compelling account of superb detective work, and unprecedented dedication of an entire police department.

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.