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Tutorial Course Descriptions

Detailed Syllabus

C-216 Practical Design of Optical Thin Films

The course is intended to be valuable to new coating engineers, scientists, technicians, and technical managers as well as seasoned thin film scientists who are involved in design, development, and production of optical thin films. Basic principles are laid out from the beginning for those new to the field, but the evolution of the topics then moves into material and techniques useful to even the more experienced practitioners. No extensive background in mathematics or physics is required; extensive graphical illustrations are used. This course deals with optical thin film coating design. It is a companion to, but not a requirement for, the course on optical thin film coating production on the following day with another book by the author. Advanced optical thin films are being used increasingly in communications, optical systems, and light control and collection applications. The sophistication of the optical coating industry is advancing rapidly to meet ever increasing demands for performance and production capability. New viewpoints, equipment, and processes are available to support advanced capability and efficiency. Objectives of this course include: to provide increased knowledge and understanding of the many practical aspects of optical coating design, to discuss the techniques and principles discussed, and to elucidate techniques and processes that are commonly successful in meeting optical coating needs.

Topical Outline:

• Firmly grasp, visualize, and use optical thin film design principles.
• Use graphical methods in thin film design.
• Estimate what can be achieved before starting a design.
• Obtaining good indexes from processes before final designs by good measurement techniques and avoiding pitfalls.
• Understand Fourier thin film synthesis and compare rugate and discrete layer designs.
• Solve practical coating design problems.

Attendees in this tutorial receive the text, Practical Design of Optical Thin Films, 4th edition, Ronald R. Willey (Willey Optical, Consultants, 2014) [printed by Lulu.com Press]

Course Details:

FUNDAMENTALS OF THIN FILM OPTICS 1

1.1. INTRODUCTION 1
1.2. REVIEW OF THIN FILM OPTICS PRINCIPLES 5
1.3. REFLECTANCE DIAGRAMS AND DESIGN 13
1.3.1. Low Reflectors, Antireflection Coatings 16
1.3.2. Why Are Bubbles Colored? 24
1.3.3. Back Of The Envelope (BOTE) Calculations 27
1.3.4. Three-Layer AR Coating on Germanium, Example 28
1.3.5. Example Four-Layer Broad Band AR Coating in the Visible 33
1.3.6. Medium Reflectors and Beamsplitters 35
1.3.7. High Reflectors and Building Blocks 36
1.3.8. Physical Thickness versus Optical Thickness 38
1.4. REFERENCES 38
 

APPLICATIONS 39
2.1. INTRODUCTION 39
2.2. DESIGNING DIELECTRIC MIRRORS 39
2.3. ESTIMATING BANDPASS AND BLOCKER COATINGS 45
2.3.1. Estimating the Width of a Blocking Band 45
2.3.2. Estimating the Optical Density of a Blocking Band 47
2.3.3. Estimating the Number of Layers and Thickness Needed 48
2.4. DICHROIC REFLECTION COATINGS 49
2.5. NARROW BANDPASS FILTERS 52
2.5.1. Behavior of a High Index Slab 53
2.5.2. High Reflectors 54
2.5.3. NBP Wavelength Effects as Seen on Reflectance Diagrams 61
2.5.4. Dense Wavelength Division Multiplexing (DWDM) Filters 64
2.5.5. Fiber Bragg Gratings 67
2.6. ESTIMATING DWDM FILTERS 67
2.6.1. Beamsplitters 71
2.7. ANGLES AND POLARIZATION 72
2.7.1. Wavelength Shift with Angle of Incidence 72
2.7.2. Polarization Effects of Angle of Incidence 73
2.7.3. Tilting for Tuning the Wavelength of a Filter 76
2.7.4. Polarization as Seen in Reflectance Amplitude Diagrams 78
2.7.5. Polarizing Beamsplitters 80
2.7.6. Non-Polarizing Beamsplitters 83
2.8. ADDITIONAL VIEWS VIA GRAPHICS AND PLOTS 88
2.8.1. Admittance Diagrams 88
2.8.2. Ellipsometry Plots 92
2.8.3. Additional Graphics for Visualization 100
2.9. APPROXIMATIONS OF INDICES AND DESIGNS 101
2.9.1. Herpin/Epstein Periods 101
2.9.2. More General Approximations 102
2.10. INHOMOGENEOUS INDEX FUNCTIONS 106
2.10.1. Step-Down Functions 106
2.10.2. Low Index Limitations 115
2.10.3. Lithographic “Moth-Eye” ARs 117
2.10.4. Overcoming Low Index Limitations With Thickness 119
2.10.5. Additional Thickness Functions 119
2.11. A FOURIER APPROACH 125
2.12. REFERENCES 130


ABSORBING MATERIALS 133
3.1. TRIANGLE DIAGRAMS AND DESIGN 133
3.2. DESIGNING COATINGS WITH ABSORBING MATERIALS 137
3.3. INDUCED TRANSMITTANCE FILTER 155
3.4. NBP REFLECTANCE FILTER EXAMPLE 158
3.5. NEUTRAL DENSITY FILTER EXAMPLE 161
3.6. CONCLUSIONS OF DESIGNING WITH METALS 167
3.7. REFERENCES 167


ADVANCED DESIGN 169
4.1. HIGHER HARMONIC REFLECTION BANDS 169
4.2. MINUS FILTERS AND NARROW BLOCKING BANDS 176
4.3. FENCEPOST AND POSTHOLE DESIGN APPROACHES 180
4.3.1. Fencepost Design Examples 184
4.3.2. Edge Filters 187
4.3.3. Fencepost Narrow Bandpass Filters 189
4.3.4. Estimating OD and BW of Fenceposts 192
4.4. RUGATES AND EUV/SOFT X-RAY SPECTRAL REGION 196
4.5. QUANTIZATION EFFECTS IN EUV/X-RAY MIRRORS 208
4.6. FOURIER VIEWPOINT OF OPTICAL COATINGS 214
4.6.1. Fourier Concepts 214
4.6.2. Background 216
4.6.3. Some Limitations 224
4.6.4. A Method to Determine the Multiple Reflections 230
4.6.5. Fourier Summary 232
4.7. ESTIMATING EDGE FILTER PASSBAND REFLECTION 233
4.7.1. Procedure 237
4.7.2. Equations 239
4.7.3. Bandwidth Limitations on SWP Filters 242
4.7.4. Design Limitations of QWOT Stack SWP Filters 243
4.7.5. When Wider Passbands Are Needed for SWP Edge Filters 244
4.7.6. Optical Density and Band Edge Steepness 249
4.7.7. Squareness Between Edge and Passband 251
4.7.8. Wide Passband SWP Filters Conclusions 251
4.8. REFERENCES 253


MEASUREMENTS 257

5.1. INTRODUCTION 257
5.2. SPECTROPHOTOMETERS 258
5.2.1 Dispersive Spectrometers and Spectrophotometers 258
5.2.2 Interferometric Spectrometers and Spectrophotometers 262
5.2.3 Fourier Transform Infrared versus Grating Instruments 270
5.2.4 Types of Reflecting Surfaces 275
5.2.5 The Original Recording Spectrophotometer 276
5.3. MEASURING %TRANSMITTANCE & %REFLECTANCE 278
5.3.1. Measuring Transmittance 278
5.3.2. Potential Measurement Problems 280
5.3.3. Measuring Reflectance 282
5.3.4. Checking Linearity of Reflectance Measurements 288
5.3.5. Other Reflectance Measurements 292
5.3.6. Photodiode Array Spectrometers 295
 

FINDING INDICES AND TOOLING FACTORS 313
6.1 INDEX & THICKNESS DETERMINATION 313
6.1.1. Index of Refraction Determination 314
6.1.2. Fitting Values for High Index Materials 315
6.1.3. Piecewise Fitting Using $NK in FilmStar 325
6.1.4. Fitting Values for Low Index Materials 327
6.1.5. Using the FilmStar Software Package for Index Fitting 328
6.1.6. Another Index Test Method 333


DESIGNING COATINGS 349
7.1. INTRODUCTION 349
7.2. ANTIREFLECTION COATINGS 349
7.2.1. Procedure 350
7.2.2. The Formula 351
7.2.3. Results 353
7.2.4. Berlin AR Design Contest 357
7.2.5. Results of Further Study 360
7.2.6. Estimating the Number of Layers 365
7.2.7. Looking Outside the Box 367
7.2.8. Reverse Engineering Using Number of Ripples in Band 370
7.2.9. Summary of Antireflection Coating Estimation 371
7.3. OPTIMIZATION 372
7.3.1. Performance Goals and Weightings 372
7.3.2. Global versus Local Minima 374
7.3.3. Some Optimizing Concepts 375
7.3.4. Constraints 379
7.3.5. Quantization 381
7.4. DESIGNING A VERY BROAD BAND AR 384
7.4.1. Specific Example 385
7.4.2. Design Extension to Three Bands 393
7.5. OTHER EXAMPLES 395
7.6. REFERENCES 399
 

Appendix Table of Conversion Factors 401
Index 405


 

Instructor: Ronald R. Willey, Consultant, Willey Optical
Ronald R. Willey

graduated from the MIT in optical instrumentation, has an M.S. from FIT, and over 40 years of experience in optical system and coating development and production. He is very experienced in practical thin films design, process development, and the application of industrial Design of Experiments methodology. He is the inventor of a robust plasma/ion source for optical coating applications. He worked in optical instrument development and production at Perkin-Elmer and Block Associates. He developed automatic lens design programs at United Aircraft Research Laboratories. He formed Willey Corporation in 1964 and served a wide variety of clients with consulting, development, prototypes, and production. In 1981 he joined Martin Marietta Aerospace and was Director of the Optical Component Center where he was responsible for optical fabrication, coating, and assembly. He joined Opto Mechanik in 1985 where he was responsible for the development of all new technologies, new instruments, and production engineering. He was a Staff Scientist at Hughes Danbury Optical Systems. He holds four patents and has published many papers on optical coating design and production, optical design, and economics of optical tolerances. He has published books on optical thin film coating design and production since 1996. His recent books are “Practical Design of Optical Thin Films”, 4th Ed. (2014) and “Practical Production of Optical Thin Films,” 2nd Ed. (2012) He is a fellow of the Optical Society of America and SPIE and a past Director of the Society of Vacuum Coaters. He now is a consultant in the above-listed technical and forensic areas. Here he is concentrating on teaching optical thin film design and production, and also aiding clients in process development and improvement.


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