A selection of some optical with polished optical surfaces for various applications The Properties of Optical

Springer-Verlag Berlin Heidelberg GmbH Schott Series on Glass and Glass Ceramics Science, Technology, and Applications

Low Thermal Expansion Glass Ceramics ISBN 3-540-58598-2

Fibre and Glass Integrated Optics ISBN 3-540-58595-8

The Properties of Optical Glass ISBN 3-540-58357-2

Thin Films on Glass ISBN 3-540-58597-4

Electrochemistry of Glasses and Glass Melts Including Glass Electrodes ISBN 3-540-58608-3

Surface Analysis of Glasses, and Glass Ceramics, and Coatings ISBN 3-540-58609-1

Analysis of the Composition and Structure of Glass and Glass Ceramics ISBN 3-540-58610-5 Hans Bach Norbert Neuroth Editors The Properties of Optical Glass

With 161 Figures, 62 Tables, and 2 Fold-out Diagrams

i Springer Editors: Dr. Hans Bach Dr. Norbert Neuroth Schott Glas, Hattenbergstr. 10 D-5S122 ,

Second Corrected Printing 1998

ISBN 978-3-642-63349-2 ISBN 978-3-642-57769-7 (eBook) DOI 10.1007/978-3-642-57769-7 CIP-data applied for This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on micro-film or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer-Verlag. Violations are liable for prosecution under the German Copyright Law. © Springer-Verlag Berlin Heidelberg 1995, 1998 Originally published by Springer-Verlag Berlin Heidelberg New York in 1995, 1998 Softcover reprint of the hardcover 1st edition 1995, 1998

The use of designations, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the rele• vant protective laws and regulations and therefore free for general use. The type designations applied to optical glasses are the Type Designations for Optical Glasses which have been developed by and are industrial property rights of Schott, e.g. BaK 50, BK 7, FK 5, LaK 13, SF 6, SK 16. Registered trademarks used in this book (relevant pages in italics): Athermal 373,374,375, UroH9 378, Duran 213, 219, High-Lite 266, 271, Neotherm 402, Schott BK7 254, Tessar 253, Ultran 20 297,301, Uvilex 402, Zerodur 254. Cover Design: Meta Design Berlin Typesetting: TEX data conversion by Kurt Mattes, Heidelberg using Springer makro package.

Printed on acid-free paper SPIN 10640624 56/3142 543210 Foreword

This book, entitled The Properties of Optical Glass, is one of a series reporting on research and development activities on products and processes conducted by the Schott Group.

The scientifically founded development of new products and technical processes has traditionally been of vital importance at Schott and has always been per• formed on a scale determined by the prospects for application of our special glasses. The scale has increased enormously since the reconstruction of the Schott Glaswerke in Mainz. The range of expert knowledge required for that could never have been supplied by Schott alone. It is also a tradition in our company to cultivate collaboration with customers, universities, and research institutes. Publications in numerous technical journals, which since 1969 we have edited to a regular timeplan as Forschungsberichte - 'research reports' - formed the basis of this cooperation. They contain up-to-date information on the most var• ious topics for the expert but are not suited as survey material for those whose standpoint is more remote. This is the point where we would like to place our series, to stimulate the exchange of thoughts, so that we can consider from different points of view the possibilities offered by those incredibly versatile materials, glass and glass ceramics. We would like to show scientists and engineers, interested customers, and friends and employees of our firm the knowledge that has been won through our research and development at Schott in cooperation with the users of our materials. The results documented in the volumes of the Schott Series are of course ori• ented to the tasks and targets of a company. We believe it will become quite clear that here readers can nevertheless - or rather for that reason - find demand• ing challenges for applied research, the development of process engineering, and characterization of measurement practice. Besides realizability, the profitability of solutions to customers' problems always plays a decisive role. The first comprehensive presentation of research findings after the recon• struction of the factory in Mainz was edited by Prof. Dr. Dr. h.c. Erich Schott in 1959. It was entitled Beitriige z'ur angewandten Glasforschung - 'contribu• tions to applied glass research' (Wissenschaftliche Verlagsgesellschaft m.b.H., Stuttgart 1959). Since then, there has been an extraordinary worldwide increase VI Foreword in the application of glass and glass ceramic materials. Glass fibres and compo• nents manufactured from them for use in lighting and traffic engineering or in telecommunications, high-purity and highly homogeneous glasses for masks and projection lenses in electronics, or glass ceramics with zero expansion in astron• omy and in household appliance technology are only some examples. In many of these fields Schott has made essential contributions. Due to the breadth and complexity of the field in which Schott is active, many volumes are needed to describe the company's research and development results. Otherwise it would be impossible to do full justice to the results of fundamental research work and technological development needed for product development. Furthermore, it is necessary to give an appropriate description of the methods of measurement and analysis needed for the development and manufacture of new products. The next two volumes, which will be published within about a year, will be entitled Low Thermal Expansion Glass Ceramics and Thin Films on Glass. Another four volumes treating fibre optics and integrated optics, surface analysis, analysis of the composition and structure of glass and glass ceramics, and the electrochemistry of glasses and glass melts are in preparation. Descriptions of melting and processing technology and of glasses for various applications in industry and science and their properties are being considered. With the presentation - in part detailed - of the work required for the devel• opment of successful products, Schott employees are giving all their interested colleagues who work in the field of science and technology an insight into the spe• cial experiences and successes in material science, material development, and the application of materials at Schott. Contributions from scientists and engineers who work in university and other research institutes and who played an essential role in Schott developments complete the survey of what has been achieved. At the same time such results show the need for the collaboration mentioned above. In all the volumes of the series the fundamental issues from chemistry, physics, and engineering are dealt with, or at least works are cited that en• able or assist the reader to work his or her way into the topics treated. vVe see this as indispensable because, with the series, Schott has a further goal in view. We aim to provide all future business partners from branches of industry where glasses and glass ceramics have not been applied so far with knowledge they can use in cooperation with Schott. Furthermore, the series may serve to fill gaps between the basic knowledge imparted by material science and the product de• scriptions published by Schott. Those who have already done business with our company may find the survey of fundamentals useful in extending collaboration to further business areas. To make each volume sufficiently intelligible, the necessary fundamentals from chemistry, physics, and engineering are described or referred to via cita• tions. We see this as the best way to enable all our potential business partners who are not already familiar with glass and glass ceramics to compare these materials with alternatives on a thoroughly scientific basis. We hope that this Foreword VII will lead to intensive technical discussions and collaborations on new fields of application of our materials and products, to our mutual advantage. Every volume of the Schott Series will begin with a chapter providing a general idea of the current problems, results, and trends relating to the subjects treated. These introductory chapters and the reviews of the basic principles are intended to be useful for all those who are dealing for the first time with the special properties of glass and glass ceramic materials and their surface treatment in engineering, science, and education. Many of our German clients are accustomed to reading scientific and tech• nical publications in English, and most of our foreign customers have a better knowledge of English than of the German language. It was therefore mandatory to publish the Schott Series in English. The publication of the Schott Series has been substantially supported by Springer-Verlag. We would like to express our special thanks to Dr. H.K.V. Lotsch and Dr. H.J. Kolsch for advice and assistance in this project. The investment of resources by Schott and its employees to produce the Schott Series is, as already stated, necessary for the interdisciplinary dialogue and collaboration that are traditional at Schott. A model we still find exemplary today of a fruitful dialogue between fundamental research, glass research, and glass manufacture was achieved in the collaboration of Ernst Abbe, Otto Schott, and Carl Zeiss. It resulted in the manufacture of optical that realized in practice the maximum theoretically achievable resolution. It was especially such experiences that shaped the formulation of the founding statute of the Carl Zeiss Foundation, and the initiative for the Schott Series is in accord with the commitment expressed in the founding statute "to promote methodical scientific studies."

Mainz, January 1995 Dieter Krause Vice President R&D Preface to the Second Corrected Printing

The second edition contains two new sections: "Environmentally Friendly Op• tical Glasses" , and "Optical Materials for Microlithography". Both are fields of recent activities. Besides these additions, several corrections have been made. We thank Mrs. Karin Langner-Bahmann for the computer processing of the figures, Mrs. Wiltrud Witan, M.A., for revising the English, and the authors for reading, correcting, and updating their contributions. Additionally, we are indebted to Dr. Victoria Wicks, Springer-Verlag, for copy-editing this edition.

Summer 1998 Hans Bach Norbert Neuroth Preface to the First Edition

The main aim of the Schott Series volume The Properties of Optical Glass is to describe the properties of the optical glasses developed by Schott. The book is conceived as a monograph. However, the individual chapters have been written by different - sometimes by several - authors who are themselves active in the corresponding fields of research and development. Thus the reader is given direct access to the experience of these authors, some of whom are employed in our subsidiaries Schott Glass Technologies, Duryea, USA; Deutsche Spezialglas AG, Griinenplan; and Carl Zeiss, Oberkochen. To give the reader a view of the extraordinarily broad range of applications of glasses and glass components, the volume opens with a general survey of the development of optical glasses and their important fields of application, and the aims, limits, and current state of new developments and trends in application. The subsequent chapters treat the properties of optical glasses and other special glasses. Schott has significantly contributed to the development and pro• duction technology of these glasses since the establishment of the company more than 100 years ago. Information is provided, above all, on properties that are important for the application of optical glasses as classical optical elements such as lenses and prisms. The reader should develop a deeper understanding of opti• cal glass as a material and at the same time find answers to particular questions such as: Within what limits can the properties of glasses for optical service be manufactured reprodUcibly? How does the material glass behave in processing? Which chemical and physical influences have to be considered in the application of optical glasses? In addition, an insight into special applications in optoelec• tronics is given. In these chapters, the latest results from the Schott laboratories on the properties of optical glasses are reported. Due to their vital importance for the construction and manufacture of op• tical instruments, the mechanical and thermal properties of optical glasses and the influence of thermal treatment on the optical constants are also considered. The influence of the tempering of glasses on their structure and the resulting change in their properties, however, will be treated together with the analysis of glasses in a subsequent volume. This division seems appropriate because for an adequate characterization of the properties of a glass, for many kinds of applica• tion, both an elemental analysis and a characterization of the structure through spectroscopy and other analytical methods are required. Preface to the First Edition XI

For the production and utilization of optical surfaces the interaction between the surfaces of optical glasses with aqueous solutions and gases in the atmo• sphere, especially the water vapour contained in the air, is of great importance. Methods for the practical determination of chemical properties and the differ• ences in the resistance of optical glasses resulting from them are therefore treated in a separate chapter. The following chapter describes results and experiences gathered during the production of optical surfaces. The chapter explains which mechanical and chemical interaction parameters must be taken into account in the manufacture of optical surfaces in order to obtain the best possible yields. New developments and examples of the application of special optical glasses for opthalmics, the ultraviolet and infrared spectral regions, photochromic glasses, glasses for lasers, glasses for nuclear engineering, and coloured and pro• tection glasses are the subjects of individual sections in the final chapter. In all the contributions, descriptions in the text and tables and examples are chosen so as to assist the user of the material glass, especially the constructor of optical equipment, in his or her daily work with the material and components made from it. The form of the presentation and the selection of citations can also be useful for teaching and research, especially in those cases where data for measuring and analysis techniques are required. The cited literature should support the reader in gaining access to more detailed presentations to deepen his or her knowledge. The contributions in this volume fill the gap between the basic knowledge of glass and its properties provided by material science, on the one hand, and catalogue data supplied by glass manufacturers on the other. In view of the amount of material to be covered, the description of the pro• duction of raw glass and of semimanufactured and finished products, including sol-gel techniques, requires its own volume in the Schott Series. For the same reason, separate volumes must also be reserved for the coating of glass surfaces and the production of optical fibres for light guides and image guides and for integrated optics. We would like to thank all the authors of this book for their steady and pleasing cooperation. We have received further valuable help from many colleagues. For critical reading of the manuscripts we thank Mrs. Marga Faulstich, Dr. habil. Walter Geffcken, Dipl.-Phys. Alfred Jacobsen, Dipl.-Phys. Hans Morian, Dr. Burkhard Speit, at Schott Glas, Mainz, Dr. Alexander J. Marker III, at Schott Glass Technologies, Duryea, and Prof. Dr. Hans-Jiirgen Hoffmann, at the Technical University, Berlin. Additionally, we are indebted to several employees of Springer-Verlag, espe• cially Barbara S. Hellbarth-Busch, Petra Treiber, and Peter Strafier, for helping us to overcome the difficulties involved in producing manuscripts ready for print• ing. For their help in solving text processing problems we are indebted to Urda Beiglbock and Frank Holzwarth, also of Springer-Verlag. XII Preface to the First Edition

We are grateful to Dipl.-Math. Sieglinde Quast-Stein, Schott Glas, who with her knowledge and experience provided substantial support in the implementa• tion of the software guidelines supplied by Springer-Verlag. We also thank Dipl.-Designer Andreas Jacobsen, Niedernhausen, for the cre• ation of the numerous computer graphics needed to illustrate the texts. We would especially like to thank Mrs. Angela Gamp-Paritschke, M.A., Schott Glas, for the translation from German into English, for the correction of manuscripts submitted in English, and for her enthusiasm in performing all the hard work necessary to prepare manuscripts ready for printing.

January 1995 Hans Bach Norbert Neuroth Table of Contents

1 Overview - Optical Glass: An Engineered Material Alexander J. Marker III, Norbert Neuroth...... 1 1.1 Glass: An Important Material for Optics ...... 1 1.2 Essential Properties...... 2 1.3 History of Development ...... 3 1.4 Selected Applications ...... 4 1.5 Progress in Manufacturing Technology ...... 6 1.6 Today's Interests...... 7 References ...... 11

2 Optical Properties Marc K. Th. Clement, Joseph S. Hayden, Yuiko T. Hayden, Hans-Jiirgen Hoffmann, Uwe Kolberg, Frank-Thomas Lentes, Norbert Neuroth, Silke Wolff ...... " 19 2.1 Refractive Index and Dispersion Frank-Thomas Lentes ...... 19 2.1.1 Introduction...... 19 2.1.2 Law of Refraction ...... " 19 2.1.3 Dispersion and the Various Dispersion Formulae...... 20 2.1.4 Measurement and Limitations of the Accuracy of Refractive Index Data ...... " 27 2.1.5 Definition of the Characteristic Properties of Optical Glasses...... 29 2.2 The Chemical Composition of Optical Glasses and Its Influence on the Optical Properties Marc K. Th. Clement...... 58 2.2.1 General Remarks ...... " 58 2.2.2 Glass Types ...... 65 2.2.3 Reduction of the Density ...... " 72 2.2.4 Development of Optical Glasses ...... 73 2.3 Transmission and Reflection Norbert Neuroth...... 82 2.3.1 General Relations ...... 82 2.3.2 Sources of Optical Loss in Glass ...... " 85 2.3.3 Examples of Transmission Spectra ...... " 90 2.3.4 Influence of Temperature...... 93 2.3.5 Influence of Radiation on the Transmission ...... 94 XIV Table of Contents

2.4 Differential Changes of the Refractive Index Hans-Jurgen Hoffmann...... 96 2.4.1 General Remarks...... 96 2.4.2 The Refractive Index of Air and Its Variations ...... 97 2.4.3 Thermal Treatment of Glasses and the Refractive Index.. 99 2.4.4 The Thermo-Optical Coefficient ...... 104 2.4.5 Photoelastic Properties of Glasses ...... 107 2.4.6 The Electro-Optic Effect in Glasses (Kerr-Effect) ...... 114 2.4.7 Magneto-Optic Effects in Glasses ...... 115 2.4.8 Further Possibilities ...... 120 2.5 Acousto-Optical Properties of Glasses Hans-Jurgen Hoffmann . 123 2.5.1 Acousto-Optical Effects and Applications ...... 123 2.5.2 Characterization of Glasses ...... 125 2.6 Nonlinear Optical Properties Yuiko T. Hayden, Joseph -8. Hayden ...... 130 2.6.1 Homogeneous Glasses ...... 131 2.6.2 Heterogeneous Glasses - Semiconductor-Doped Glasses ... 134 2.6.3 Heterogeneous Glasses - Metallic-Particle-Doped Glasses. 137 2.6.4 Heterogeneous Glasses - Other Systems ...... 138 2.7 Resistance to Laser Radiation Joseph S. Hayden ...... 139 2.7.1 Bulk Damage Resistance to Laser Radiation ...... 139 2.7.2 Surface Damage Resistance to Laser Irradiation ...... 142 2.7.3 Multiphoton Darkening of Optical Glass ...... 144 2.8 Environmentally Friendly Optical Glass Silke Wolff, Uwe Kolberg ...... 144 References ...... 149

3 Optical Quality Frank-Thomas Lentes, Norbert Neuroth ...... 165 3.1 Uniformity and Tolerances of the Refractive Index and the Abbe Number ...... 165 3.2 Colouration, Solarization and Fluorescence ...... 170 References ...... 175

4 Mechanical Properties Kurt N attermann, Norbert Neuroth, Robert J. Scheller ...... 179 4.1 Density ...... 179 4.2 Elastic Modulus, Poisson's Ratio, Specific Thermal Tension ..... 179 4.3 Microhardness ...... 183 4.4 Strength of Glasses ...... 187 4.4.1 Introduction ...... 187 4.4.2 Brittle Fracture of Glass ...... 188 4.4.3 Fractography ...... 190 4.4.4 Sub-Critical Crack Growth ...... 191 4.4.5 Fracture Probability ...... 192 Table of Contents XV

4.4.6 Testing of Glasses ...... 194 4.4.7 Three-Point Bending...... 194 4.4.8 Ring-on-Ring Test ...... 195 4.5 Strengthening of Glass ...... 196 4.5.1 Thermal Strengthening ...... 196 4.5.2 Chemical Strengthening ...... 197 References ...... 198

5 Thermal Properties of Glass Ulrich Fotheringham ...... 201 5.1 Heat Capacity ...... 201 5.2 Thermal Conductivity ...... 209 5.2.1 The Phononic Contribution to the Thermal Conductivity. 210 5.2.2 The Radiative Heat Transfer in Opaque Glass ...... 211 5.2.3 The Radiative Heat Transfer in Transparent Glass ...... 213 5.3 Thermal Expansion ...... 220 5.4 Viscosity ...... 223 References ...... 227

6 Chemical Durability of Optical Glass: Testing Methods - Basic Information, Comparison of Methods Applied by Different Manufacturers and International Testing Standards Wilfried Heimerl, Arnd Peters ...... 229 6.1 Introduction ...... 229 6.2 General Chemical Reactions with Water (Neutral Aqueous Solutions) on the Glass Surface ...... 230 6.3 Processing and Chemical Reactions ...... 231 6.4 Cleaning and Its Possible Effects ...... 232 6.5 Testing Methods ...... 232 6.5.1 International Standard Procedures ...... 233 6.5.2 Comparison of Methods for Testing the Chemical Durability of Optical Glasses, Using Solid Polished Glass Plates as Samples ...... 239 6.5.3 Comparison of Methods for Testing the Chemical Durability of Optical Glasses Using Powdered Glass as Sample ...... 241 6.6 Discussion ...... 242 References ...... 243

7 Processing (Grinding and Polishing) Knut Holger Fiedler ...... 245 7.1 Introduction ...... 245 7.1.1 Grinding and Polishing ...... 245 7.1.2 Material Removal Rate ...... " ... " ...... 246 XVI Table of Contents

7.1.3 Historical Background ...... 246 7.2 Glass Grinding ...... 247 7.2.1 Indentation and Scratching ...... 247 7.2.2 Loose Abrasive Grinding ...... 248 7.2.3 Fixed Abrasive Grinding ...... 249 7.3 Glass Polishing ...... 252 7.3.1 Full Lap Polishing Techniques ...... 252 7.3.2 Sub-aperture Polishing ...... 256 7.3.3 Influences of Chemistry in Glass Polishing ...... 256 7.4 Advanced Material Removal Techniques ...... 258 7.5 Conclusion and Future Work ...... 258 References ...... 259

8 Selected Applications Joseph S. Hayden, Ewald Hillmann, Hans-Jurgen Hoffmann, Uwe Kolberg, David Krashkevich, Clemens Kunisch, Monika J. Liepmann, Susan R. Loehr, Peter NajJ, Norbert Neuroth, Thomas Schindelbeck, Burkhard Speit, Thomas Westerhoff ...... 263 8.1 Ophthalmic Glasses David Krashkevich, Susan R. Loehr ...... 263 8.1.1 History of Ophthalmic Lenses ...... 263 8.1.2 The Optics of Vision and Ophthalmic Lenses ...... 263 8.1.3 Properties of Ophthalmic Glasses ...... 267 8.1.4 Multifocal Ophthalmic Lenses ...... 268 8.1.5 Strengthening of Ophthalmic Lenses ...... 270 8.2 Photochromic Glasses Hans-Jiirgen Hoffmann ...... 273 8.2.1 Basic Principles of Photochromic Effects ...... 273 8.2.2 Photochromic Oxidic Glasses Doped with Silver Halides .. 274 8.2.3 Qualitative Description of the Darkening and the Regeneration Mechanisms of the Photochromic Glasses ... 279 8.2.4 Photochemical Reaction Kinetics in Photo chromic Glasses 281 8.2.5 Generalisations and Consequences ...... 286 8.2.6 Conclusions ...... 287 8.3 Ultraviolet-Transmitting Glasses Monika J. Liepmann, Norbert Neuroth ...... 288 8.3.1 Intrinsic Absorption ...... 288 8.3.2 Effects of Impurities ...... 294 8.3.3 Commercial Glasses ...... 295 8.4 Infrared-Transmitting Glasses Monika J. Liepmann, Norbert Neuroth ...... '.' ..... 297 8.4.1 Sources of Absorption ...... 297 8.4.2 Oxide Glasses ...... 398 8.4.3 Halide Glasses ...... 301 8.4.4 Chalcogenide Glasses ...... 303 8.4.5 Commercial Glasses ...... 308 Table of Contents XVII

8.5 Laser Glasses Joseph S. Hayden, Norbert Neuroth ...... 308 8.5.1 Requirements for Laser Glass Materials ...... 308 8.5.2 Activating Ions ...... 312 8.5.3 Glass Development ...... 314 8.5.4 Process Development ...... 317 8.5.5 Commercial Neodymium Laser Glasses ...... 320 8.5.6 Functional Forms of Laser Glass ...... 321 8.5.7 Applications of Laser Glass and Future Development Trends ...... 323 8.6 Glasses for High Energy Particle Detectors Susan R. Loehr, Peter NajJ, Burkhard Speit ...... 324 8.6.1 Introduction ...... 324 8.6.2 X-Ray Sensitive Glasses ...... 325 8.6.3 Scintillating Glass Calorimeter ...... 327 8.6.4 Cerenkov Glass Counters ...... 329 8.6.5 Active Glasses for Scintillating Fibres ...... 331 8.6.6 Glass Capillaries Filled with Liquid Scintillator for High-Resolution Detectors ...... 334 8.7 Special Glasses for Nuclear Technologies Burkhard Speit ...... 340 8.7.1 Radiation-Shielding Glasses ...... 340 8.7.2 Radiation-Resistant Optical Glasses ...... 343 8.7.3 Dosimeter Glasses ...... 346 8.7.4 Glasses for Nuclear Fusion ...... 348 8.8 Coloured Glasses Uwe Kolberg ...... 350 8.8.1 Introduction ...... 350 8.8.2 The Basics of Colour Generation in Glasses ...... 354 8.8.3 Trends in the Development of Coloured Glasses at Schott. 367 8.9 Glasses for Eye Protection Ewald Hillmann, Norbert Neuroth . . 370 8.9.1 The Eye ...... 370 8.9.2 Protective Glasses ...... 370 8.10 Optical Materials for Microlithography Clemens Kunisch, Thomas Schindelbeck, Thomas Westerhoff ...... 380 8.10.1 Optical Microlithography ...... 380 8.10.2 i-Line Glass ...... 381 8.10.3 Fused Silica (Si02) and CaF2 ...... 386 References ...... 388

List of Contributing Authors ...... 403

Sources of Figures and Tables ...... 405

Index ...... 409