70-5542 Mckenney, Dean Brinton, 1940- ULTRAVIOLET
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ULTRAVIOLET INTERFERENCE FILTERS WITH METAL-DIELECTRIC STACKS Item Type text; Dissertation-Reproduction (electronic) Authors McKenney, Dean B. Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 04/10/2021 00:45:19 Link to Item http://hdl.handle.net/10150/287430 This dissertation has been microfilmed exactly as received 70-5542 McKENNEY, Dean Brinton, 1940- ULTRAVIOLET INTERFERENCE FILTERS WITH METAL-DIELECTRIC STACKS. University of Arizona, Ph.D., 1969 Physics, optics University Microfilms, Inc., Ann Arbor, Michigan ULTRAVIOLET INTERFERENCE FILTERS WITH METAL-DIELECTRIC STACKS by Dean Brinton McKenney A Dissertation Submitted to the Faculty of the OPTICAL SCIENCES COMMITTEE In Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY In the Graduate College THE UNIVERSITY OF ARIZONA 19 6 9 THE UNIVERSITY OF ARIZONA GRADUATE COLLEGE I hereby recommend that this dissertation prepared under my direction by Dean Brinton McKenney entitled Ultraviolet Interference Filters with Metal-Dielectric Stacks be accepted as fulfilling the dissertation requirement of the degree of Doctor of Philosophy After inspection of the final copy of the dissertation, the following members of the Final Examination Committee concur in its approval and recommend its acceptance:* Vj /74>; K. A/. VL&L net —l— This approval and acceptance is contingentlent on/ the candiccandidate's adequate performance and defense of this dissertation at the final oral examination. The inclusion of this sheet bound into the library copy of the dissertation is evidence of satisfactory performance at the final examination. STATEMENT BY AUTHOR This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona anc is deposited in the University Library to be made available to bor rowers under rules of the Library. Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or re production of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the in terests of scholarship. In all other instances, however, permission must be obtained from the author. / SIGNED; "A ACKNOWLEDGMENTS I would like to thank the following persons for their contri butions to this research: Dr. A. F. Turner for his help in selecting the research topic and his suggestions and guidance during the re search; Dr. W. G. Tifft for making the coating apparatus available for this work; Dr. 0. N. Stavroudis for many inspiring discussions; Dr. S. F. Jacobs for his encouragement and support; Mr. C. E. Nalley, Jr. for his laboratory assistance; Mr. J. Poulos for several helpful suggestions; and Mr. W. P. Jenny for assistance with the monitor electronics. This work has been supported in part by: The National Aeronautics and Space Administration through an institutional grant NGR-03-002-091, contract NAS8-20651, and grant NGR 03-002-032; The United States Air Force contract F04695-67-C-0197; and a Department of Defense THEMIS Contract F44620-69-C-0024. Ill TABLE OF CONTENTS LIST OF ILLUSTRATIONS vi LIST OF TABLES ix ABSTRACT x I, INTRODUCTION 1 Ultraviolet Filters 1 History of Reflection Filters 4 Description of the Research 8 II. COMPUTED PROPERTIES OF METAL-DIELECTRIC STACKS 12 Computation of the Electromagnetic Fields 13 Definitions of the Optical Properties 24 Mirror Reflection Filters as Solar Blind Mirrors 31 Admittance Properties of Multilayers and Antireflection 40 The Pauli Expansion Matrix 47 Herpin's Theorem for Reversible Stacks 52 Applications of DMD Stacks to Ultraviolet Filters 56 The Single Film Equivalents for DMD Stacks 63 III. EXPERIMENTAL PROPERTIES OF METAL-DIELECTRIC STACKS 89 Evaporation and Vacuum 90 The Vacuum System 94 The Film Thickness Monitor 99 Laboratory Procedures 105 Experimental Properties of Mirror Reflection Filters 110 Experimental Properties of Single DMD Stacks 114 Experimental Properties of Multiple DMD Stacks... 118 Empirical Filter Designs 125 IV. CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE RESEARCH 131 Suggestions for Future Research 133 APPENDIX A. THE DERIVATION OF THE CHARACTERISTIC MATRIX FROM ASSUMED WAVE FUNCTIONS 135 iv V TABLE OF CONTENTS—Continued APPENDIX B. PROPERTIES OF SINGLE METAL FILMS 137 REFERENCES 143 LIST OF ILLUSTRATIONS Figure Page 1. Schematic Diagram Showing Nomenclature Used to Describe a Multilayer Filter ; 15 2. The Effect of Dispersion on the Computed Optical Properties 34 3. The Effect of Changing the Thickness of the Semitransparent Layer of the Aluminum, Magnesium Fluoride, Aluminum Mirror Reflection Filter 37 4. The Computed Reflectance of a Chromium, Magnesium Fluoride, Aluminum Mirror Reflection Filter 39 5. Diagram Showing the Nomenclature Used to Describe the Antireflection Stack 45 6. Vector Diagram Showing the Formation of Reversible Stacks . 51 7. The Computed Properties of (DMD)*5 Stacks with Different Numbers of Periods p 57 8. The Computed Properties of (DMD)^ Stacks with Different Metal Thicknesses h^ 58 9. The Computed Reflectance of a (DMD)8 Filter 60 10. The Computed Properties of a DMD Fabry-Perot Filter 64 .wV 11. The Equivalent Admittance and Thickness of a (DMD) Stack with 10 run Thick Metal Layers 66 12. The Equivalent Admittance and Thickness of a (DMD) Stack with 5 nm Thick Metal Layers 67 13. The Equivalent Admittance and Thickness of a (MDM) Stack with 2.5 nm Thick Metal Layers 69 14. The Computed Reflectances of (DMD)00 Stacks with Metal Thicknesses of 5 nm and 10 nm 72 vi LIST OF ILLUSTRATIONS—Continued Figure Page 15. The Computed Reflectance of a (MDM)°° Stack with Metal Thicknesses of 2.5 73 16. The Load Admittance Required to Antireflect the Stacks (DMD)1 and (DMD)2 79 17. The Load Admittance Required to Antireflect the . Stacks (DMD)1 and (DMD)1* 81 18. The Admittance of the Stack (DMD)°° in Air 83 19. The Reflectance of a Modified Mirror Reflection Filter ... 86 20. The Computed Reflectance of a Modified (DMD) Reflection Filter 87 21. Schematic Diagram of the Ultrahigh Vacuum System 95 22. Schematic Diagram of the Optical Thickness Monitor 101 23. Schematic Diagram of the Electronic Circuit for the Film Thickness Monitor 104 24. The Measured Reflectance of an Aluminum, Magnesium Fluoride, Aluminum Mirror Reflection Filter Ill 25. The Measured Reflectance of an Aluminum, Magnesium Fluoride, Chromium Mirror Reflection Filter 113 26. Comparison Between the Computed and Measured Transmittances and Reflectances of a Single DMD Period for Several Values of the Metal Thickness 116 27. The Measured Reflectance and Transmittance for a (DMD)2 filter 120 28. The Reflectance and Transmittance of a (DMD)3 Filter .... 122 29. The Reflectance and Transmittance of a (DMD)1* Filter .... 123 30. The Effect of Dielectric Layer Thickness Errors on the Optical Properties of the (DMD)1* Filter 124 31. The Reflectance and Transmittance of a (DMD)5 Filter .... 127 viii LIST OF ILLUSTRATIONS—Continued Figure Page 32. The Measured Reflectance of the Filter (DM^D)3(DM2D)1 ... 128 33. The Computed Reflectance of the Filter (DMjD)3(DM2D)1 . 130 34. The Reflectances and Transmittances of Different Absorbing Films 139 35. The Reflectance and Transmittance of Very Thin Metal Films in Air . 141 \ \*\ S i LIST. OF TABLES Table Uge 1. The Optical Constants of Evaporated Aluminum 33 2. The Design Details for the Modified DMD and Mirror Reflection Filters . 88 3. Some Vacuum Properties of Nitrogen 93 V ix ABSTRACT This investigation represents a systematic study of a class of metal-dielectric interference filters which would be suitable for use in the ultraviolet. General techniques for designing filters containing many metal layers are developed and are applied specifi cally to the design of ultraviolet reflection filters with magnesium fluoride and aluminum. That some of these filters can be realized experimentally is demonstrated. The problem of designing and describing the properties of general metal-dielectric stacks is considered. The accepted computa tional method is extended to include the dispersion of the optical constants. Formal conditions for antireflecting with a metal-dielec- tric stack are derived. These general conditions for antireflection reduce, in the all-dielectric case, to the well-known complex conjugate admittance matching theorem. The characteristic thin film matrix is expanded in terms of the Pauli spin matrices in vector form. This gives a geometrical representation of the conditions under which a stack of films is equivalent to a single film. This special case of Herpin's theorem allows the properties of a stack of the form (DMD)P - a Dielectric-Metal-Dielectric stack repeated p times - to be represented by two complex quantities: the equivalent characteristic admittance and the equivalent phase thickness. The computed properties of specific DMD stacks with magnesium fluoride and aluminum are applied to the design of ultraviolet filters. We have found that a high reflection band is formed around the region where the optical thicknesses of the dielectric layers is X/4. The width of the high reflection band is shown to depend on the thicknesses of the metal layers, narrower reflection bands being produced by thinner metal layers. We find that the long-wavelength reflectance also depends on the metal layer thicknesses. A solar-blind mirror design was found that consists of eight DMD periods with an aluminum layer thickness of 4.3 nm. TTie equivalent film properties are applied to the design of DMD stacks with different metal layer thicknesses for each period. Two examples of filters with low long-wavelength reflectances obtained with a minimum metal layer thickness of 7 nm are given.