Search

This book provides a comprehensive analysis of quantum-confined semiconductor lasers, focusing on quantum dot lasers (QDLs) and interband quantum cascade lasers (ICLs). Through theoretical and numerical exploration, the author scrutinizes the amplitude and frequency noise spectra, studies the dynamics induced by delayed optical reinjection, and investigates the generation of squeezed states for both laser types. Notably, his predictions align with experimental results, demonstrating the robustness of this approach. Structured meticulously, the book begins with an overview of QDL and ICL technology, followed by in-depth chapters on classical noise and dynamics, and quantum aspects, particularly the generation of squeezed states. Clearly written, the text strikes a balance between words and equations, maintaining accessibility without sacrificing depth. It includes an extensive bibliography, a testament to the thoroughness of the research and a useful feature for all newcomers to the field.

This book focuses on the design, materials, process, fabrication, and reliability of flip chip, hybrid bonding, fan-in, and fan-out technology. Both principles and engineering practice have been addressed, with more weight placed on engineering practice. This is achieved by providing in-depth study on a number of major topics such as wafer bumping, flip chip assembly, underfill and reliability, chip-to-wafer, wafer-to-wafer, Cu-Cu hybrid bonding, WLCSP, 6-side molded WLCSP, FOWLP such as hybrid substrates with PID, ABF, and ultra-large organic interposer, the communications between chiplets and heterogeneous integration packaging, and on-board optics, near-package optics, and co-packaged optics.The book benefits researchers, engineers, and graduate students in the fields of electrical engineering, mechanical engineering, materials sciences, industry engineering, etc.

This book highlights recent advances in novel optical fiber sensing technology and systems, using distributed fiber sensing technology based on chaotic lasers. Upon introducing the basic theory of chaotic laser, a novel light source, the book summarizes new frontier technologies, and presents photonic integration and sensing applications. The book elaborates on new technologies of distributed optical fiber sensors and its engineering applications, as well as narrow-linewidth fiber laser for optical fiber sensing. This book is of great reference for researchers and professionals in the area of optics and optoelectronics.

This book analyzes the development of space light-fiber coupling research, highlights its importance, examines the underlying theory and key problems, and elaborates on methods to improve the space light-fiber coupling efficiency. Starting from the basic theory of electromagnetic field, the transmission characteristics of light in optical fibers are expounded, and the coupling characteristics of optical signals of different modes are investigated. The spatial light-fiber coupling techniques such as mode conversion method, lens coupling method, and wavefront distortion correction method are discussed in detail, and the key technologies involved are verified by experiments. This book is suitable for the vast majority of engineering and technical personnel and teachers in colleges and institutions who are engaged in wireless optical communication. It can also be used to train senior undergraduates and graduate students in relevant fields.

This thesis investigates passively mode-locked semiconductor lasers by numerical methods. The understanding and optimization of such devices is crucial to the advancement of technologies such as optical data communication and dual comb spectroscopy. The focus of the thesis is therefore on the development of efficient numerical models, which are able both to perform larger parameter studies and to provide quantitative predictions. Along with that, visualization and evaluation techniques for the rich spatio-temporal laser dynamics are developed; these facilitate the physical interpretation of the observed features.The investigations in this thesis revolve around two specific semiconductor devices, namely a monolithically integrated three-section tapered quantum-dot laser and a V-shaped external cavity laser. In both cases, the simulations closely tie in with experimental results, which have been obtained in collaboration with the TU Darmstadt and the ETH Zurich. Based on the successful numerical reproduction of the experimental findings, the emission dynamics of both lasers can be understood in terms of the cavity geometry and the active medium dynamics. The latter, in particular, highlights the value of the developed simulation tools, since the fast charge-carrier dynamics are generally not experimentally accessible during mode-locking operation. Lastly, the numerical models are used to perform laser design explorations and thus to derive recommendations for further optimizations.

This handbook provides a comprehensive review of the entire field of laser micro and nano processing, including not only a detailed introduction to individual laser processing techniques but also the fundamentals of laser-matter interaction and lasers, optics, equipment, diagnostics, as well as monitoring and measurement techniques for laser processing. Consisting of 11 sections, each composed of 4 to 6 chapters written by leading experts in the relevant field. Each main part of the handbook is supervised by its own part editor(s) so that high-quality content as well as completeness are assured. The book provides essential scientific and technical information to researchers and engineers already working in the field as well as students and young scientists planning to work in the area in the future. Lasers found application in materials processing practically since their invention in 1960, and are currently used widely in manufacturing. The main driving force behind this fact is that the lasers can provide unique solutions in material processing with high quality, high efficiency, high flexibility, high resolution, versatility and low environmental load. Macro-processing based on thermal process using infrared lasers such as CO2 lasers has been the mainstream in the early stages, while research and development of micro- and nano-processing are becoming increasingly more active as short wavelength and/or short pulse width lasers have been developed. In particular, recent advances in ultrafast lasers have opened up a new avenue to laser material processing due to the capabilities of ultrahigh precision micro- and nanofabrication of diverse materials. This handbook is the first book covering the basics, the state-of-the-art and important applications of the dynamic and rapidly expanding discipline of laser micro- and nanoengineering. This comprehensive source makes readers familiar with a broad spectrum of approaches to solve all relevant problems in science and technology. This handbook is the ultimate desk reference for all people working in the field.

This fourth book in the series Silicon Photonics gathers together reviews of recent advances in the field of silicon photonics that go beyond already established and applied concepts in this technology. The field of research and development in silicon photonics has moved beyond improvements of integrated circuits fabricated with complementary metal–oxide–semiconductor (CMOS) technology to applications in engineering, physics, chemistry, materials science, biology, and medicine. The chapters provided in this book by experts in their fields thus cover not only new research into the highly desired goal of light production in Group IV materials, but also new measurement regimes and novel technologies, particularly in information processing and telecommunication. The book is suited for graduate students, established scientists, and research engineers who want to update their knowledge in these new topics.

This comprehensive handbook gives a fully updated guide to lasers and laser technologies, including the complete range of their technical applications. This forth volume covers laser applications in the medical, metrology and communications fields. Key Features: • Offers a complete update of the original, bestselling work, including many brand-new chapters.• Deepens the introduction to fundamentals, from laser design and fabrication to host matrices for solid-state lasers, energy level diagrams, hosting materials, dopant energy levels, and lasers based on nonlinear effects.• Covers new laser types, including quantum cascade lasers, silicon-based lasers, titanium sapphire lasers, terahertz lasers, bismuth-doped fiber lasers, and diode-pumped alkali lasers.• Discusses the latest applications, e.g., lasers in microscopy, high-speed imaging, attosecond metrology, 3D printing, optical atomic clocks, time-resolved spectroscopy, polarization and profile measurements, pulse measurements, and laser-induced fluorescence detection.• Adds new sections on laser materials processing, laser spectroscopy, lasers in imaging, lasers in environmental sciences, and lasers in communications. This handbook is the ideal companion for scientists, engineers, and students working with lasers, including those in optics, electrical engineering, physics, chemistry, biomedicine, and other relevant areas.

This book provides a comprehensive overview of the state-of-the-art in the development of semiconductor nanostructures and nanophotonic devices. It covers epitaxial growth processes for GaAs- and GaN-based quantum dots and quantum wells, describes the fundamental optical, electronic, and vibronic properties of nanomaterials, and addresses the design and realization of various nanophotonic devices. These include energy-efficient and high-speed vertical cavity surface emitting lasers (VCSELs) and ultra-small metal-cavity nano-lasers for applications in multi-terabus systems; silicon photonic I/O engines based on the hybrid integration of VCSELs for highly efficient chip-to-chip communication; electrically driven quantum key systems based on q-bit and entangled photon emitters and their implementation in real information networks; and AlGaN-based deep UV laser diodes for applications in medical diagnostics, gas sensing, spectroscopy, and 3D printing. The experimental results are accompanied by reviews of theoretical models that describe nanophotonic devices and their base materials. The book details how optical transitions in the active materials, such as semiconductor quantum dots and quantum wells, can be described using a quantum approach to the dynamics of solid-state electrons under quantum confinement and their interaction with phonons, as well as their external pumping by electrical currents. With its broad and detailed scope, this book is indeed a cutting-edge resource for researchers, engineers and graduate-level students in the area of semiconductor materials, optoelectronic devices and photonic systems.

This book highlights recent advances and applications in terahertz (THz) technology, addressing advanced topics such as THz biomedical imaging, pattern recognition and tomographic reconstruction for THz biomedical imaging by machine learning and artificial intelligence, THz imaging radars for autonomous vehicle applications, and THz imaging systems for security and surveillance. It also discusses theoretical, experimental, established and validated empirical work on these topics.

Dieses Nachschlagewerk wendet sich vor allem an Ingenieure und Physiker in der Telekommunikationsindustrie, bei Netzbetreibern und in der Datenkommunikation. Weiterhin kann es diesen Nutzern sowie Wissenschaftlern und Studenten einen Überblick über das Fachgebiet verschaffen und die Einarbeitung in speziellere Felder ermöglichen. Die grundlegenden Beziehungen und Technologien werden zusammengestellt und in ihren wesentlichen Zügen erläutert. Grafische Darstellungen und Abbildungen vermitteln die Zusammenhänge anschaulich und ingenieurgerecht. Zu dem Werk haben maßgebliche Forscher und Industrieingenieure aus dem deutschen Sprachraum beigetragen. Als Vorbild für die Konzeption diente das Standardwerk über Hochfrequenztechnik von MEINKE und GUNDLACH.

This book brings together the recent cutting-edge work on computational methods in photonics and their applications. The latest advances in techniques such as the Discontinuous Galerkin Time Domain method, Finite Element Time Domain method, Finite Difference Time Domain method as well as their applications are presented. Key aspects such as modelling of non-linear effects (Second Harmonic Generation, lasing in fibers, including gain nonlinearity in metamaterials), the acousto-optic effect, and the hydrodynamic model to explain electron response in nanoplasmonic structures are included. The application areas covered include plasmonics, metamaterials, photonic crystals, dielectric waveguides, fiber lasers. The chapters give a representative survey of the corresponding area.

This book describes the fascinating recent advances made concerning the chaos, stability and instability of semiconductor lasers, and discusses their applications and future prospects in detail. It emphasizes the dynamics in semiconductor lasers by optical and electronic feedback, optical injection, and injection current modulation. Applications of semiconductor laser chaos, control and noise, and semiconductor lasers are also demonstrated.Semiconductor lasers with new structures, such as vertical-cavity surface-emitting lasers and broad-area semiconductor lasers, are intriguing and promising devices. Current topics include fast physical number generation using chaotic semiconductor lasers for secure communication, development of chaos, quantum-dot semiconductor lasers and quantum-cascade semiconductor lasers, and vertical-cavity surface-emitting lasers.This fourth edition has been significantly expanded to reflect the latest developments. The fundamental theory oflaser chaos and the chaotic dynamics in semiconductor lasers are discussed, but also for example the method of self-mixing interferometry in quantum-cascade lasers, which is indispensable in practical applications.Further, this edition covers chaos synchronization between two lasers and the application to secure optical communications. Another new topic is the consistency and synchronization property of many coupled semiconductor lasers in connection with the analogy of the dynamics between synaptic neurons and chaotic semiconductor lasers, which are compatible nonlinear dynamic elements. In particular, zero-lag synchronization between distant neurons plays a crucial role for information processing in the brain. Lastly, the book presents an application of the consistency and synchronization property in chaotic semiconductor lasers, namely a type of neuro-inspired information processing referred to as reservoir computing.

Presenting a blend of applied and fundamental research in highly interdisciplinary subjects of rapidly developing areas, this book contains contributions on the frontiers and hot topics of laser physics, laser technology and laser engineering, and covers a wide range of laser topics, from all-optical signal processing and chaotic optical communication to production of superwicking surfaces, correction of extremely high-power beams, and generation of ultrabroadband spectra. It presents both review-type contributions and well researched and documented case studies, and is intended for graduate students, young scientist, and emeritus scientist working/studying in laser physics, optoelectronics, optics, photonics, and adjacent areas. The book contains both experimental and theoretical studies, as well as combinations of these two, which is known to be a most useful and interesting form of reporting scientific results, allowing students to really learn from each contribution. The book contains over 130 illustrations.

This book provides a comprehensive review of the state-of-the art of optical signal processing technologies and devices. It presents breakthrough solutions for enabling a pervasive use of optics in data communication and signal storage applications. It presents presents optical signal processing as solution to overcome the capacity crunch in communication networks. The book content ranges from the development of innovative materials and devices, such as graphene and slow light structures, to the use of nonlinear optics for secure quantum information processing and overcoming the classical Shannon limit on channel capacity and microwave signal processing.Although it holds the promise for a substantial speed improvement, today's communication infrastructure optics remains largely confined to the signal transport layer, as it lags behind electronics as far as signal processing is concerned. This situation will change in the near future as the tremendous growth of data traffic requires energy efficient and fully transparent all-optical networks. The book is written by leaders in the field.

The contributions in this volume were presented at a NATO Advanced Study Institute held in Erice, Italy, 4-19 July 2013. Many aspects of important research into nanophotonics, plasmonics, semiconductor materials and devices, instrumentation for bio sensing to name just a few, are covered in depth in this volume. The growing connection between optics and electronics, due to the increasing important role plaid by semiconductor materials and devices, find their expression in the term photonics, which also reflects the importance of the photon aspect of light in the description of the performance of several optical systems. Nano-structures have unique capabilities that allow the enhanced performance of processes of interest in optical and photonic devices. In particular these structures permit the nanoscale manipulation of photons, electrons and atoms; they represent a very hot topic of research and are relevant to many devices and applications.The various subjects bridge over the disciplines of physics, biology and chemistry, making this volume of interest to people working in these fields. The emphasis is on the principles behind each technique and on examining the full potential of each technique.

Laser Diode Microsystems provides the reader with the basic knowledge and understanding required for using semiconductor laser diodes in optical microsystems and micro-optical electromechanic systems. This tutorial addresses the fundamentals of semiconductor laser operation and design, coupled with an overview of the types of laser diodes suitable for use in Microsystems, along with their distinguishing characteristics. Emphasis is placed on laser diode characterization and measurement as well as the assembly techniques and optical accessories required for incorporation of semiconductor lasers into complex microsystems. Equipped with typical results and calculation examples, this hand-on text helps readers to develop a feel for how to choose a laser diode, characterize it and incorporate it into a microsystem.

Optical networks are leaving the labs and becoming a reality. Despite the current crisis of the telecom industry, our everyday life increasingly depends on communication networks for information exchange, medicine, education, data transfer, commerce, and many other endeavours. High capacity links are required by the large futemet traffic demand, and optical networks remain one of the most promising technologies for meeting these needs. WDM systems are today widely deployed, thanks to low-cost at extreme data rates and high reliability of optical components, such as optical amplifiers and fixed/tunable filters and transceivers. Access and metropolitan area networks are increasingly based on optical technologies to overcome the electronic bottleneck at the network edge. Traditional multi-layer architectures, such as the widely deployed IP/ATM/SDH protocol stack, are increasingly based on WDM transport; further efforts are sought to move at the optical layer more of the functionalities available today in higher protocol layers. New components and subsystems for very high speed optical networks offer new design opportunities to network operators and designers. The trends towards dynamically configurable all-optical network infrastructures open up a wide range of new network engineering and design choices, which must face issues such as interoperability and unified control and management.

Optical communications networks are an essential part of the world wide te- communication infrastructure. The number of users of present and future telecommunication services like Internet, web browsing and tele-education is expected to increase dramatically. As a consequence there is an imminent - mand for high broadband and high capacity communication systems. A prom- ing solution is found in the concept of all-optical networks. These networks exploit the vast capacity of the optical fiber by using multiplexing techniques that allow for an overall capacity of terabits per second. Channels are routed and switched in the optical domain. In this manner data channels are carried from the receiver side to its destination making use of optical transmission techniques. Wavelength division multiplexing (WDM) is a transmission technique that has dramatically increased the capacity of optical transmission systems. WDM allows for transmission of several channels over a single optical fiber by - ing different wavelength as the channel carrier. Optical switching and routing techniques are also being developed to cope with the high data speeds and n- ber of channel carried in the optical fibers. These functionalities are provided by optical crossconnects. The use of transmission techniques such as WDM in combination with optical crossconnects is enabling optical networking at high bit-rates reaching terabits per second. These techniques also offer ways to improve the network flexibility and configurability.

Sizes of electronic and photonic devices are decreasing drastically in order to increase the degree of integration for large-capacity and ultrahigh­ speed signal transmission and information processing. This miniaturization must be rapidly progressed from now onward. For this progress, the sizes of materials for composing these devices will be also decreased to several nanometers. If such a nanometer-sized material is combined with the photons and/or some other fields, it can exhibit specific characters, which are considerably different from those ofbulky macroscopic systems. This combined system has been called as a mesoscopic system. The first purpose of this book is to study the physics of the mesoscopic system. For this study, it is essential to diagnose the characteristics of miniaturized devices and materials with the spatial resolution as high as several nanometers or even higher. Therefore, novel methods, e.g., scanning probe microscopy, should be developed for such the high-resolution diagnostics. The second purpose of this book is to explore the possibility of developing new methods for these diagnostics by utilizing local interaction between materials and electron, photon, atomic force, and so on. Conformation and structure of the materials of the mesoscopic system can be modified by enhancing the local interaction between the materials and electromagnetic field. This modification can suggest the possibility of novel nano-fabrication methods. The third purpose of this book is to explore the methods for such nano-fabrication.

The motivation to collect contributions from a wide variety of subjects in cont- porary optics, centered around optical imaging, originates from two ideas. First, it is easy to recognise that certain?elds of contemporary optics have been devel- ing in quite a parallel manner. Sometimes workers of the di?erent?elds discover each other's contributions, but mostly they do not. One of our major goals is to show how closely these contributions are inter-related. Such an example is the - velopment of scanning/confocal optical microscopy and optical data storage. In the former, imaging in the classical sense, occurs by scanning a tightly focused laser beam over the sample. In optical data storage imaging does not occur as the aim is to detect pits, rather than to image them. Nevertheless, the optical systems of these two arrangements have striking resemblance and hence their governing equations are practically the same. The second motivation of this book is to collect contri- tions from imaging related subjects that were not previously published in this form or they are di?cult to access. Such examples are a chapter on white light interfer- etry, surface plasmon microscopy or the characterisation of high numerical aperture microscope objective lenses. We are extremely pleased that we have contributions in this book from the - ternational leaders of individual?elds. It has been our privilege to work with these authors and we would like to take this opportunity to thank them all.

Photonic Crystals are the newest types of optical material being developed for commercial applications in industry. They are likely to provide an exciting new tool for the manipulations of photons and have received the attention of both academia and industry. Roadmap on Photonic Crystals gives a detailed explanation of the background of photonic crystals, the theories behind them, numerical simulations, crystal structures, fabrication processes, evaluation methods and proposed applications. This also includes a roadmap addressing future development and applications. Industrial scientists, post-doctoral researchers and graduate students will find Roadmap on Photonic Crystals a useful tool in the understanding of the critical aspects of photonic crystals.

Interference coatings are an essential part of modern optics. This book is designed to give a concise but complete overview of the field, with contributions written by leading experts in the various areas. Topics include design, materials, film growth, deposition including large area, characterization and monitoring, and mechanical stress. The authors also describe applications in astronomy, microcomponents, DUV/VUV, EUV/X, ultrafast optics, displays, and ultrasensitive fluorescence. Furthermore, laser-resistant coatings and coatings for free-electron lasers and plastic optics are covered. The book concludes with chapters on photonic structures as interference devices and on the brilliant world of natural coatings.

Photonic Crystals details recent progress in the study of photonic crystals, ranging from fundamental aspects to up-to-date applications, in one unified treatment. It covers most of the worldwide frontier fields in photonic crystals, including up-to-date fabrication techniques, recent and future technological applications, and our basic understanding of the various optical properties of photonic crystals. Brand-new theoretical and experimental data are also presented. The book is intended for graduate course students and specialists actively working in this field, but it will also be useful for newcomers, especially the extensive chapter dealing with fundamental aspects of photonic crystals, which paves the way to a full appreciation of the other topics addressed.

The book gives an in-depth description of the key devices of current and next generation fibre optic communication networks. In particular, the book covers devices such as semiconductor lasers, optical amplifiers, modulators, wavelength filters, and detectors but the relevant properties of optical fibres as well. The presentations include the physical principles underlying the various devices, the technologies used for the realization of the different devices, typical performance characteristics and limitations, and development trends towards more advanced components are also illustrated. Thus the scope of the book spans relevant principles, state-of-the-art implementations, the status of current research and expected future components.

Nonlinear optical phenomena can be exploited in advanced devices for transport, processing, and storage of information. These are needed as the present-day approach - mainly using on electron-based technology - faces the challenges of increasing demand on bandwidth and processing speed. A key role in the development of nonlinear devices is the availability of novel materials with the required nonlinear optical properties. With such materials, scientific creativity and careful design, promising concepts have been developed resulting in the demonstration of devices. This book contains the proceedings of NOIS 2000 (Nonlinear Optics for the Information Society) Annual Meeting of the COST Action P2, held at the University of Twente, in Enschede, The Netherlands, on 26-27 October, 2000. It comprises a selection of the presentations at the meeting, reporting state-of-the-art research and developments in the field of applications of nonlinear phenomena in information technology.

Modern communication technologies have revolutionized society and econ­ omy on a global scale, and progress in this field is still breathtaking. Among the crucial features of these developments is the possibility to transmit/receive ever-increasing bit rates at lower and lower cost. This is due to some ex­ tent to improved electronics, but it is much more due to the capabilities of opticaL fibre-based communication systems. Optical communication tech­ nologies were initially introduced in order to improve traditional information exchange, but they have recently become a key prerequisite for the tremen­ dous growth in internet traffic, and optical technologies will be even more important in enabling and supporting the future expansion of internet traffic with annual growth rates forecast at 100%-200%. It is the purpose of the present book to describe the enabling components of optical communication systems, in particular their fundamentals, principles and current status, as well as the potential for future developments. Following such a scheme, it is the editors'hope that this book will not only attract the attention of experts already working in the field, but be, at least, likewise directed to interested newcomers. The book is organized into eleven chapters addressing the essential optical and optoelectronic components which form the hardware basis of today's, and most likely of future, optical networks.

This book summarizes the proceedings of the invited talks presented at the International Symposium on New Trends in Optical Soliton Transmission Systems held in Kyoto during November 18 - 21, 1997. As a result of worldwide demand for ultra high bitrate transmissions and increased scientific interest from the soliton community, research on optical solitons in fibres has made remarkable progress in recent years. In view of these trends, the Research Group for Optical Soliton Communications (ROSC), chaired by Akira Hasegawa, was established in Japan in April 1995 to promote collaboration and information exchange among communication service companies, industries and academic circles in the theory and application of optical solitons. This symposium was organized as a part of the ROSC activities. As with the 1 st ROSC symposium, this symposium attracted enthusiastic response from worldwide researchers involved in the subject of soliton based communications and intensive discussions were held throughout the symposium. Particular emphases were made to dispersion managements of soliton transmission. I would like to note that in the }'t symposium the (adiabatic) dispersion managements just began to appear in reducing radiation at amplifiers and reducing collision effects in WDM system. These have become standard this time, but in addition new, non-adiabatic dispersion managements have been introduced independently by various scientists all over the world.

The transmission speed of data communication systems is forecast to increase exponentially over the next decade. Development of both Si-based high-speed drivers as well as III-V-semiconductor-based high-speed vertical cavity surface emitting lasers (VCSELs) are prerequisites for future ultrahigh data-rate systems. This thesis presents: - a survey of the present state of the art of VCSELs - a systematic investigation of the various effects limiting present VCSELs - a catalogue of solutions to overcome present limits - detailed progress in modelling, fabricating and testing the currently most advanced VCSELs at the two commercially most important wavelengths.

It has been four years since the publication of the?rst edition of this book. During these four years optical imaging has advanced considerably. Nevertheless, when we were asked to compile a second edition of this book the?rst question we asked was: are there any topics that were missed out from the?rst edition? Even though there are a fairly large number of subjects that we could potentially have considered it was decided to extend the book by two new chapters. The?rst one is on the use of di?ractive optical elements in high quality objective lenses by Drs Brunner and Dobschal from Carl Zeiss AG. It is particularly exciting to have this chapter in the book because it is likely that di?ractive elements will play an increasingly imp- tant role in high precision optical instrumentation in the future. The second new chapter is by Daniel Axelrod of University of Michigan on total internal re?ection?uorescence (TIRF). We believe that many readers will?nd the chapter from Prof. Axelrod, who developed TIRF about 20 years ago, insightful and very interesting. In addition to the new chapters some chapters have been revised and consid- ably expanded. These revisions are primarily there to include the most up-to-date material and recent advances of the?eld. Special note of thanks must go to Drs Claus Ascheron and Angela Lahee of Springer-Verlagfor their encouragementand help.