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Spie Press Book

Field Guide to Optical Thin Films
Author(s): Ronald R. Willey
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Book Description

This Guide covers the principles and applications of various useful graphical tools and methods for optical coating design, including the reflectance diagram, admittance diagram, and triangle diagram. These tools give insight into how optical coatings function and how they might be designed to meet given requirements. Shown are how unavailable indices can be approximated, the basis of ideal antireflection coating design, and the practical approximation of inhomogeneous index profiles.

Book Details

Date Published: 27 January 2006
Pages: 118
ISBN: 9780819462183
Volume: FG07

Table of Contents
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Glossary x
Fundamentals of Thin Film Optics 1
Optical Basic Concepts 1
Internal Angles in Thin Films 2
Reflection 3
Reflections 4
Example Reflection Calculations 5
Graphics for Visualization of Coating Behavior 6
Reflectance as Vector Addition 6
Reflectance Amplitude Diagram 7
Admittance Diagram 8
Electric Field in a Coating 9
Admittance versus Reflectance Amplitude Diagrams 10
Triangle Diagram 11
Behavior of Some Simple AR Coating Types 12
Single-Layer Antireflection Coating 12
Two-Layer AR Amplitude Diagram Example 13
Wavelength Effects 14
Broad-Band AR Coating 17
Two V-Coat Possibilities 18
Index of Refraction Simulations and Approximations 19
Effective Index of Refraction 19
Complex Effective Index Plot 20
Simulating One Index With Two Others 21
Herpin Equivalent Layers 22
Approximations of One Index with Others 23
The QWOT Stack, a Coating Building Block 24
QWOT Stack Reflectors 25
QWOT Stack Properties 26
Width of the Block Band 28
Applications of the QWOT Stack 29
Absentee Layer 30
Narrow Band Pass Filter 31
Optical Density and Decibels (db) 32
NBP Filter Design 33
Multiple-Cavity NBP 34
Rabbit Ears 36
Coatings at Non-Normal Angles of Incidence 37
Polarization Effects 37
Wavelength Shift with Angle of Incidence 38
Angle of Incidence Effects in Coatings 39
Polarizing Beamsplitters 40
Polarization as Viewed in Circle Diagrams 41
Non-Polarizing Beamsplitters in General 43
A Non-Polarizing Beamsplitter Design Procedure 44
Non-Polarizing BS's Found & Rules-of-Thumb 46
Coatings with Absorption 47
Various Metals on Triangle Diagrams 47
Chromium Metal Details 48
A Design Example Using Chromium 50
Potential Transmittance 52
Understanding Behavior and Estimating a Coating's Potential 53
Estimating What Can Be Done Before Designing 53
Effects of Last Layer Index on BBAR Coatings 54
Effects of Index Difference (H-L) on BBAR Coatings 55
Bandwidth Effects on BBAR Coatings 56
Bandwidth Effects Background 57
Estimating the Rave of a BBAR 59
Estimating the Minimum Number of Layers in a BBAR 60
Bandpass and Blocker Coatings 61
Mirror Estimating Example Using ODBWP 63
Estimating Edge Steepness in Bandpass Filters 64
Estimating Bandwidths of Narrow Bandpass Filters 65
Blocking Bands at Higher Harmonics of a QWOT Stack 68
Insight Gained from Hypothetical Cases 71
'Step-Down' Index of Refraction AR Coatings 71
Too Much Overall Thickness in a Design 74
Inhomogeneous Index of Refraction Designs 75
Possibility of Synthesizing Designs 77
Fourier Concepts 77
Fourier Background 78
Fourier Examples 80
Fourier Limitations 82
Designing Various Types of Coatings 84
Designing a New Coating 84
Designing BBAR Coatings 85
Tails in BBAR Coatings 87
Designing Edge Filters, High Reflectors, Polarizing
and Non-Polarizing Beamsplitters 89
Designing Beamsplitters in General 90
Designing to a Spectral Shape & Computer Optimization 91
Performance Goals and Weightings 92
Constraints 93
Global vs. Local Minima 94
Some Optimizing Concepts 94
Damped Least Squares Optimization 95
Needle Optimization 95
Flip-Flop Optimization 96
Equation Summary 97
Bibliography 101
Index 102


The principles of optical thin films are reviewed and applications shown of various useful graphical tools (or methods) for optical coating design: the reflectance diagram, admittance diagram, and triangle Diagram. It is shown graphically how unavailable indices can be approximated by two available indices of higher and lower values than the one to be approximated. The basis of ideal antireflection coating design is shown empirically. The practical approximation of these inhomogeneous index profiles is demonstrated. Much of the discussions center on AR coatings, but most other coating types are seen in the perspective of the same graphics and underlying principles. Reflection control is the basis of essentially all dielectric optical coatings; and transmittance, optical density, etc., are byproducts of reflection (and absorption). The best insight is gained by the study of reflectance. It is also shown that AR coatings, high reflectors, and edge filters are all in the same family of designs. The graphical tools described are found to be useful as an aid to understanding and insight with respect to how optical coatings function and how they might be designed to meet given requirements.

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