The idea of using periodic magnetic fields for properly bending the trajectories of relativistic electrons, and making them generate coherent tunable radiation, appeared as early as the middle of the last century. Further study of this subject, concerning both fundamentals and practice, received a new impetus at the beginning of the seventies. Since then, a huge amount of knowledge has been accumulated in this rapidly developing field of research, creating a new class of lasers, the free electron lasers | DIGITAL COMMUNICATION Edited by C. Palanisamy Digital Communication Edited by C. Palanisamy Published by InTech Janeza Trdine 9 51000 Rijeka Croatia Copyright 2012 InTech All chapters are Open Access distributed under the Creative Commons Attribution license which allows users to download copy and build upon published articles even for commercial purposes as long as the author and publisher are properly credited which ensures maximum dissemination and a wider impact of our publications. After this work has been published by InTech authors have the right to republish it in whole or part in any publication of which they are the author and to make other personal use of the work. Any republication referencing or personal use of the work must explicitly identify the original source. As for readers this license allows users to download copy and build upon published chapters even for commercial purposes as long as the author and publisher are properly credited which ensures maximum dissemination and a wider impact of our publications. Notice Statements and opinions expressed in the chapters are these of the individual contributors and not necessarily those of the editors or publisher. No responsibility is accepted for the accuracy of information contained in the published chapters. The publisher assumes no responsibility for any damage or injury to persons or property arising out of the use of any materials instructions methods or ideas contained in the book. Publishing Process Manager Marina Jozipovic Technical Editor Teodora Smiljanic Cover Designer InTech Design Team First published March 2012 Printed in Croatia A free online edition of this book is available at Additional hard copies can be obtained from orders@ Digital Communication Edited by C. Palanisamy p. cm. ISBN 978-953-51-0215-1 INTECH open science I open minds free online editions of InTech Books and Journals can be found at .
