Coherence and Energy Transfer in Glasses PDF
Preview Coherence and Energy Transfer in Glasses
COHERENCE AND ENERGY TRANSFER IN GLASSES NATO CONFERENCE SERIES Ecology II Systems Science III Human Factors IV Marine Sciences V Air-Sea Interactions VI Materials Science VI MATERIALS SCIENCE Volume 1 Molecular Metals Edited by William E. Hatfield Volume 2 Materials for Advanced Batteries Edited by D. W. Murphy, J. Broadhead, and B. C. H. Steele Volume 3 Adhesion in Cellulosic and Wood-Based Composites Edited by John F. Oliver Volume 4 Adhesion Problems in the Recycling of Concrete Edited by Pieter C. Kreijger Volume 5 Atomistics of Fracture Edited by R. M. Latanision and J. R. Pickens Volume 6 Electronic Structure and Properties of Hydrogen in Metals Edited by P. Jena and C. B. Satterthwaite Volume 7 Soot in Combustion Systems and Its Toxic Properties Edited by J. Lahaye and G. Prado Volume 8 Surface Modification and Alloying by Laser, lon, and Electron Beams Edited by J. M. Poate, G. Foti, and D. C. Jacobson Volume 9 Coherence and Energy Transfer in Glasses Edited by Paul A. Fleury and Brage Golding COHERENCE AND ENERGY TRANSFER IN GLASSES Edited by Paul A. Fleury and Brage Golding AT & T Bell Laboratories Murray Hill, New Jersey SPRINGER SCIENCE+BUSINESS MEDIA, LLC Library of Congress Cataloging in Publication Data NATO Workshop on Coherence and Energy Transfer in Glasses (1982: Clare College of Cambridge University) Coherence and energy transfer in glasses. (NATO conference series . VI, Materials science; v. 9) "Proceedings of the NATO Workshop on Coherence and Energy Transfer in Glasses, held at Clare College of Cambridge University, during September 1982, in Cambridge, England"- T.p. verso. "Published in cooperation with NATO Scientific Affairs Division." Includes bibliographical references and index. 1. Glass-Optical properties-Congresses. 2. Amorphous semiconductors-Con- gresses. 3. Energy transfer-Congresses. I. Fleury, Paul A. II. Golding, Brage. III. North Atlantic Treaty Organization. Scientific Affairs Division. IV. Title. V. Series. TA450.N38 1982 620.1 ' 4495 84-2160 IBSN 978-1-4684-4735-4 ISBN 978-1-4684-4733-0 (eBook) DOI 10.1007/978-1-4684-4733-0 Proceedings of the NATO Workshop on Coherence and Energy Transfer in Glasses, held at Clare College of Cambridge University, during September 1982, in Cambridge, England © 1984 Springer Science+Business Media New York Originally published by Plenum Press, New York in 1984 Softcover reprint of the hardcover 1s t edition 1984 All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic , mechanical, photocopying , microfilming, recording, or otherwise, without written permission from the Publisher PREFACE In recent years the physics of disordered systems has been one of the most active and fruitful areas of research in condensed matter science. In contrast to the considerable attention paid by conferences, schools and workshops to the static and structural aspects of glasses, there has been no forum devoted primarily to the dynamic and energetic aspects of amorphous solids. The NATO Workshop on Coherence and Energy Transfer in Glasses was organized to address this deficiency. The intent was to bring together in an intense and interactive environment, experts in several rather disparate subfields relating to the dynamics and energetics of disordered systems. This volume represents the Proceedings of that Workshop, which took place in September 1982 at Clare College of Cambridge University. Forty-three scientists from eight NATO countries participated. These included representatives from universities and industrial laboratories, as well as government research institutions. The meeting was organized into eight formal sessions and one informal session devoted entirely to unstructured discussion. Each formal session featured two comprehensive lectures. An additional 60 to 90 minutes was devoted in each session to discussions and contributions related to the lectures. Since only about 60% of the session time was devoted to formal presentations, the discussions formed an equally important part of the workshop. The chairmen and discussion leaders - as well as the workshop participants themselves - brought forth lively and illuminating discussions for each session. We have attempted to capture the essence and highlights of these in this volume, along with the lectures themselves. The opening session was intended to establish common language and to review the basic amorphography and linear response of disordered systems. Professor A. C. Wright gave a masterful and comprehensive presentation on experimental techniques and related models for the structural aspects of amorphous materials. Both conventional oxide glasses and amorphous semiconductors were reviewed. Professor E. A. Davis next surveyed the experimental situation on frequency dependent linear response in amorphous v vi Preface materials ranging from transport and dielectric measurements through higher frequency microwave and infrared phenomena. His delineation of the different signatures in temperature and frequency dependence of various microscopic phenomena contributing to the responses formed an excellent basis for many of the workshop's subsequent sessions. The second session was devoted to the low energy excitations uniquely associated with the amorphous state as probed by low temperature experiments. Thermal and acoustic phenomena in glasses below lK were reviewed by Dr. M. von Schickfus. Coherent phenomena, including phonon, photon and electric field echoes in disordered materials were reviewed by Professor J. Joffrin. Dr. Golding led a comprehensive complementary discussion on related low temperature coherent phenomena. The presentations introduced the participants to many of the ideas of energy transfer in disordered systems and in particular to the tunneling systems which were to receive increased emphasis in later sessions. Sessions 3 and 4 dealt with optical energy transfer in glasses and other solids. In Session 3, rare earth doped silicate glasses and related materials were reviewed from the point of view of a theorist by Professor D. L. Huber and by Professor W. Yen as an experimentalist. The ways in which optically active impurities in amorphous materials may be probed and may be influenced by their environment formed the main themes of these presentations. Energy propagation from one defect or impurity ion to another in amorphous media is currently a subject of some controversy. A number of competing theoretical models were compared with one another by Huber and with experimental observations by Yen. The temperature dependence of laser excited fluorescence spectra in a number of such systems remains an unresolved puzzle. Session 4 was devoted to coherent optical processes and built nicely upon the earlier sessions. Dr. R. L. Brewer described his elegant experiments on optical free induction decay in rare earth doped crystals. His experiments definitively demonstrated the rich analogs between the optical spectra of probe ions in solids and the more familiar coherent spin dynamic studies traditionally done in magnetic systems. Observations of optical phenomena with typical frequencies in the kilohertz range demonstrate the remarkable power of coherent optical techniques which permit measurement accuracies approaching one part in 1012• Although Dr. Brewer's talk involved crystals rather than glasses, in the discussion it became clear that a wealth of information and new phenomena await exploration in glassy systems using coherent optical techniques. Preface vii Some preliminary steps in that direction were described by Dr. MacFarlane who gave the second talk in the fourth session. MacFarlane's experiments on spectral hole burning in rare earth doped glasses revealed that homogeneous line widths of the impurity ions in the disordered environment could be obtained in the presence of severe inhomogeneous broadening. These early studies have already revealed a number of interesting puzzles and apparent differences regarding the manner in which energy relaxes following optical excitation of different rare earth ions and indeed different states of the same ion within the amorphous environment. Many formal analogies between these optical studies and the microwave studies at very low temperatures presented in Session 2 were elucidated in the discussion. Several opportunities for more experiments and the need for more comprehensive theories on energy transfer of both deliberately placed impurities as well as native defects in amorphous solids emerged. Session 5 emphasized the theme of optical information transfer, storage, and processing in glasses. Professor S. D. Smith described experiments on optical bistability and optical logic devices, detailed the conditions and criteria for various optical switching processes and described ,simple devices which have been already operated. Here again little effort thus far has been devoted to optimizing such phenomena in amorphous or glassy materials. But the possibility that amorphous materials (particularly chalcogenide glasses) might offer advantages both in fabrication and efficiency over the crystalline materials studied to date formed the central topic of the discussion. The second major application in optical information technology for glasses is their use as lightguide media. Dr. R. H. Stolen reviewed several nonlinear optical propagation effects in optical fibers including stimulated Raman scattering, four-wave mixing, self-phase modulation and the recently observed propagation of solitons. The subsequent discussion centered largely around solitons in terms of their potential application in real transmission systems and the differences between fiber solitons and those associated with optical and microwave self-induced transparency. The workshop focus then shifted toward semiconducting glasses. Their optical properties were reviewed by Professor P. C. Taylor, and the transport phenomena associated with both intrinsic and extrinsic defects were reviewed by Professor A. Owen. These lectures also made contact with other important traditional focus of interest in amorphous solids - localization effects. The specific natures of certain defects in both the chalcogenide glasses and in tetrahedrally-coordinated semiconductors were examined in some detail by both speakers. Taylor emphasized the emerging importance of time-resolved optical fluorescence and luminescence experiments whereby VIll Preface the migration of energy among local environments could be followed in real time, the time scale being adjustable over several orders of magnitude by changing the temperature. In the discussion the relationship between the tunneling systems studied at low temperatures in chalcogenide glasses and the photo-induced defects observed previously by both optical and spin resonance techniques was clearly brought out. Session 7 was devoted to defects in amorphous semiconductors beginning with Dr. J. c. Knight's lecture on hydrogenated amorphous silicon. He emphasized the dependence of observed properties upon preparative techniques and on incorporated defects, noting that defects have at least as profound an influence on the properties of amorphous silicon as they do in the case of crystalline silicon. Professor B. C. Cave nett then described the use of optically-detected magnetic resonance in the study of defects in amorphous materials. In addition to permitting selective pumping and selective observation of particular defect states of particular symmetries, this technique and its forthcoming time dependent modification should begin to give us insights on defects in glasses of a quality similar to those we now enjoy in crystalline materials. The final formal session of the workshop was devoted to localization phenomena. Professor D. Weaire provided an elegant description of electron localization in one, two, and three dimensions. He compared several theoretical models employed to describe these, including .scaling theories, noting that only in three dimensions do the latest theories predict a true Anderson transition between localized and de localized electronic states. The language and concepts of critical phenomena flowed throughout this talk, with Professor Weaire suggesting that it makes sense to begin to talk about scaling phenomena and exponents for the disappearance of conductivity. The final formal lecture was presented by Professor H. Gibbs. His elegant review described unsuccessful attempts to observe Anderson localization in the optically-accessible excitons in ruby, theoretical reasons for this failure, and the necessary attributes a system must have in order to exhibit the Anderson transition. Possible candidates for successful experiments were described. Following the final lecture Dr. P. A. Fleury gave a brief conference summary in which some of the central points made throughout the week were reviewed. Attention was called to analogies between the microwave low temperature experiments on the one hand and the optical experiments on the other; to the potential for optical logic devices based in amorphous materials; to the intriguing similarities and yet important differences among Preface ix solitons in resonant coherent systems on the one hand and in fiber-like extended media on the other. The observation that defects in amorphous solids must be given the same kind of care and attention traditionally accorded the crystalline materials (particularly in their influence upon both optical and electronic energy transfer and transport) was emphasized. In closing, he proposed a broader view of disorder was proposed which drew some analogies between the evolution of chaos in the time regime, and the evolution of disorder in the space regime. For example, it was noted that the evolution of turbulence in a fluid can, in certain models, proceed via the nonlinear interaction of a very few incommensurate periodicities. This leads to the speculation that it might be possible to model spatial disorder at least in one or two dimensions by a compounding of incommensurate transitions, perhaps as few as three, beginning from the ordered crystalline state. The role of fluctuations in strongly non equilibrium systems are encountered in the transition to turbulence in the time regime, offers some intriguing possibilities for exploration in the spatial regime. The atmosphere and interactive modes achieved in this meeting were every bit as important as the formal presentations themselves. They were in no small measure aided by the ambience provided by the conference setting, Clare College, and by the close proximity in which the conferees lived, ate and worked. A special note of thanks is extended to Dr. W. A. Phillips of Cambridge, who in addition to helping organize the program, leading discussions and contributing ideas, did much to identify and secure the Clare College site and to oversee the local arrangements. The workshop participants, drawn from at least four major subfields of glasses and disordered materials, from the first moment engaged in vigorous crosstalk and interactions. Indeed, every participant at some point in the conference remarked to the chairmen favorably upon the degree of interaction, level of discussion and general esprit de corps which developed throughout the week. In that regard the meeting was quite successful. The whole clearly exceeded the sum of the parts. An especially memorable note was lent to the meeting by Sir Neville Mott who addressed the conference dinner on Thursday evening. His remarks, generally in a light vein, charged the conferees with redoubling their efforts to put the traditional long-standing competition between theorists and experimentalists into a renewed state of vigor. In sum the workshop appeared to be quite successful. The chemistry among the participants was evident in all the discussions and interactions. The quality of the lectures was uniformly high as was that of the contributed
The list of books you might like
