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Highlights of my 51 years in optical design


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A revised version of an earlier post

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Highlights of my 51 years in optical design

  1. 1. My 51 years of optical design – some highlights Dave Shafer David Shafer Optical Design Fairfield, Connecticut 06824 203-259-1431
  2. 2. My early years
  3. 3. As a young boy I was always fascinated by magnifying glasses Optics is kind of like magic It was not what you do or see with it that interested me. It was the lens itself and how it did this magic.
  4. 4. Some kinds of flashlight bulbs have a very small glass lens on their tips. I used to carefully break the end off with a hammer and use the tiny lens as a high power magnifying glass – about 50X magnification
  5. 5. I also made water drop microscopes. A small drop of water can very easily give 100X magnification, but it has to be held up extremely close to your eye for you to see through it. The first single lens microscope, from 300 years ago, had a tiny glass lens and was about 250X, but a water drop works well too.
  6. 6. 1957 Sears Roebuck catalog when I was 14 I had two 100X, 200X, 300X microscopes from Sears. One I used and one I got on sale for $4.50 and took apart to get at the lenses
  7. 7. I lived on a small farm, until I went to college. We had 5,000 chickens.
  8. 8. We also had one cow, and I did not drink pasteurized milk until I went to college.
  9. 9. Our farm was very far from city lights and the night skies were very dark – perfect for astronomy. Many people have never seen a really dark sky,
  10. 10. When I was 13 years old I got a mail-order kit for grinding and polishing a 150 mm aperture telescope mirror, and something like this was the result.
  11. 11. A historical note here. Very soon after the telescope was invented something else was invented that did not exist before. Window shades.
  12. 12. I bought a small star spectroscope (100 mm long) and drew charts of the solar spectrum, with its many absorption lines. Now, over 50 years later, that exact same spectroscope costs about 10X more money.
  13. 13. I devoured these three books when I was 14 as well as the very wonderful story of the Mt. Palomar telescope.
  14. 14. I discovered for the first time, back then, that men and women see the world differently. This is still a mystery to me.
  15. 15. I found that men are relatively simple, with an off/on switch, but that women are more complicated. Who knew??
  16. 16. I was hooked on optics! When I was 15 years old I got Conrady’s two books on lens design.
  17. 17. I also got a book that was full of complicated diagrams like this one. It made optics look pretty difficult.
  18. 18. Some of this material was hard to understand but I stuck with it
  19. 19. I have always been able to focus my attention very well
  20. 20. I figured that with time I would be able to understand and communicate with math at the required level.
  21. 21. When I was in high school there were no personal computers yet and no large main frame computers that were available to the general public. I traced a few light rays through an achromatic doublet lens, with trigonometric ray tracing using tables of 6 decimal place logarithms. After you do that once you never want to do it again! But I still knew that I wanted to be a lens designer.
  22. 22. Back then in the late 1950’s there was almost nothing written about lens design so there was nowhere to get help with my study of it.
  23. 23. When I went to college in 1961 big universities had a main frame computer. Data was input using punched cards. At the University of Rochester, where I went, the Optics department was able to use this computer and students like me were able to do some simple lens design problems.
  24. 24. Back in 1961, when I was a freshman, you had to wear a U of R beanie for your first year. I have just gotten mine here. In 1965 I graduated in philosophy and then went to U of R grad school in optics.
  25. 25. While at the University of Rochester I had an electrifying experience – I met my wife
  26. 26. Her grandmother (in math), her mother (in history), herself (in English), and our daughter (in philosophy) have all gone to the U of R. That had better be me
  27. 27. She was able to see beyond my very unsophisticated exterior to my very unsophisticated interior. But I was able to convince her to accept me and we have been married for 52 years now.
  28. 28. During a summer job in 1964 at Itek Corp, I was the first to observe in the lab a spiral interference fringe. Bob Shannon came up with the correct theoretical explanation and an article about it was published in Applied Optics in 1965, while I was an undergraduate at U of R. That summer I did a lot of HeNe laser interferometer experiments in the lab The red laser would look red to me in the morning, when I started work, and would look orange and dimmer as the day went on as I stared into the laser optics more and more. Now I can look directly at the sun with no effect. Oh wait …. that was the moon.
  29. 29. In the 1950’s electro-mechanical calculators (electricity powered the calculating gears) were used to do optical raytracing. To trace one light ray through one optical surface took about 3 minutes. In the early 1960’s true digital computers (main frames) were developed and they could trace one ray-surface per second. Today an ordinary PC can trace about 30 million ray-surfaces per second.
  30. 30. Optimization of optical systems requires matrix inversion. Hand calculations or electromechanical calculators in the 1950’s did 2 X 2 matrix inversions – two variables and two aberrations. Very many of them, in sequence. Today, with my PC, I optimize complex lithographic lenses with many high-order aspherics. I can optimize several thousand rays using about 100 variables and there is an enormous matrix inversion – in just a few seconds.
  31. 31. The early lens design programs were not at all user-friendly and you had to carefully study the program manual in order to effectively work with the program. If you changed jobs you might have to learn a whole new program at the new place. I did that several times and have used ORDEALS, ACCOS, SYNOPSIS, the Perkin-Elmer in-house program, and OSLO.
  32. 32. Although computers have revolutionized optical design, there is still a big need for creative thinking by the designer, using your own mental PC
  33. 33. I have found that the best way to be creative when faced with an optical design problem, or basically any problem at all, is to question hidden assumptions. We all make unwarranted assumptions, all the time.
  34. 34. When I was a kid I bought an AM radio I made an unwarranted assumption
  35. 35. AM radio PM radio I thought I was going to have to buy two radios. (this is a joke)
  36. 36. My first job after college, in 1966, was at Itek, a small high-tech company that did military optics – mostly very high resolution reconnaissance cameras for the U-2 spy plane and for early space satellite cameras. I worked on a top-secret project there that was a new way to detect Russian submarines. Some years ago this secret technology was declassified and today you can read all about it on the internet. More about this in a moment. Submarine with its periscope above the water surface
  37. 37. The first part of my career was dominated by Cold War tensions. We were in the early days of our space programs and there was a big arms race. Sometimes rockets didn’t work right. We thought that there was a missile gap with Russia.
  38. 38. The very high altitude U-2 spy plane found during flyovers of Russia that they did not have nearly as many missiles as we had thought, in the early 1960s. This chart shows the actual reality back then, based on reconnaissance photos.
  39. 39. The CORONA satellite program took pictures over Russia and then ejected film canisters that were caught in midair. Some were missed and fell into the ocean but most were caught.This was a top secret program, based at Itek, near Boston, where I was working.
  40. 40. The timing of the film canister catch had to be very precise. The film gave further proof that the “Missile Gap” with Russia was false and that information was used as a bargaining point in the Salt Talks with Russia for arms reduction.
  41. 41. The CORONA satellite took stereo photo pairs that had certain projective distortions. Those photos were then reimaged by the Gamma Rectifier lens, which cancelled out those distortions. I worked on that design at Itek Corp. in the late 1960s. These lenses were built and then worked 24 hours a day for 10 years straight fixing spy photo distortions.
  42. 42. Back to the submarine project. Submarine with its periscope above the water surface
  43. 43. In World War I and World War II submarines would be found by looking for their periscopes sticking up above the water. Sometimes the sun would reflect off the front surface of the periscope optics, but there was also sun glint off of the water waves and it was very hard to tell them apart.
  44. 44. From an airplane the water wake left by the moving periscope could be seen. But if the submarine was moving slowly or not at all then the wake was very hard to see, like in this case here.
  45. 45. What was needed was a new and highly sensitive way to spot submarine periscopes, when they were above the surface of the water. The solution was to use optics and lasers in a new, top-secret way. This new technology was given, back in 1966, the code name “Optical Augmentation” and it is still called that today. You can look it up on the internet.
  46. 46. We all know about red eye from camera flash photos.
  47. 47. The eye retina reflects back the focused light and then it is collimated by the eye lens. It can then travel long distances backwards without spreading very much. That is why flash camera “red eyes” are so bright, like this cat. Eye retina
  48. 48. Near IR laser beam Eye retina Periscope optics A low power near-IR laser beam was sent out over the water surface, from a ship, and scanned around by 360 degrees. If there is a periscope above the water then the laser light goes down the periscope optics tube and is focused on the eye retina of the person who is looking through the periscope. That light then reflects off the retina, is collimated by the eye’s lens, and reverses its path back up the tube and out. It travels back over the water to the ship where the laser is located and a very bright “red eye” can be seen. Water level
  49. 49. The energy collection area of the periscope optics is very much larger than that of the eye by itself, so the retro-reflected signal is orders of magnitude larger and gives a huge “red eye” effect.
  50. 50. You may find this hard to believe but with this relatively simple technology a submarine periscope can be detected that is many kilometers away. The laser used is near IR instead of a visible wavelength so that the person looking through the periscope will not know that they have been detected. This same technology can be used in other ways. Airplanes can detect the eyes of soldiers looking through the sights of camouflaged anti-aircraft guns. Film or a detector array at the focus of a camera also reflects back light and that is then collimated by the camera lens on the way back out. Hidden cameras can be found this way. From the ground level a laser can detect space satellite camera optics. A pulsed laser can actually measure the distance to a hidden camera, telescope, or periscope.
  51. 51. Today you can buy several versions of this declassified technology on the internet for less than $100 and find hidden cameras in your hotel room or other places, especially those tiny pin- hole sized cameras - like on cellphones.
  52. 52. The countermeasure that can defeat this system is pathetically cheap, simple, and very low-tech. Back when I was working on this project the countermeasure ideas were at a classification level above top secret. In general most expensive high tech new weapon related systems, like that below, can be defeated at a cost well below 1% of the cost of the system that is being defeated. To date all the bogus tests of this system have been completely rigged and even then most fail. Do not believe the hype about this system.
  53. 53. The Navy now has an extremely expensive high power laser system that is designed to shoot down and burn up cruise missiles in flight. Here is a simple ultra-cheap countermeasure that defeats this laser system – have a reflective mirror coating on the whole outside of the missile. Then the incoming laser power will not be nearly enough to destroy the missile. Most will be reflected away. An ultra-cheap optics idea.
  54. 54. Early warning missile defense system (Work I did in 1972, 45 years ago). In 1971 I changed jobs and worked for a company that specialized in infra-red military optics. One project was this ----
  55. 55. If a missile from behind the earth comes over the rim of the earth it will be seen here by a satellite against a black sky, but it will be very close to an extremely bright earth, which gives an unwanted signal that vastly exceeds the missile’s infra-red heat signal. But that is the easy case. Much worse is when the satellite is on the night side and the missile is seen against a sun-lit earth’s limb.
  56. 56. With the sun behind the horizon, the earth’s limb is ten orders of magnitude brighter than the missile’s infra-red heat signal.
  57. 57. Astronomers use a special kind of telescope, a coronoscope, to look at the sun’s corona. They need to block out the light from the body of the sun and just look at the sun’s edge. This is possible using a “Lyot stop” and this very old technology was used in missile defense satellite optics. It can block out very bright light that is just outside the field of view of the telescope and which is being diffracted into that field of view. That unwanted diffracted light can be many orders of magnitude brighter than the dim signal that the telescope wants to see, in its field of view.
  58. 58. Rim of aperture stop is source of diffracted light Light from earth limb Second aperture stop is smaller than image of first stop, and it blocks out-of-field diffracted light from earth limb. Lyot stop principle Two confocal parabolic mirrors give well-corrected afocal imagery Field of view rays Diffracted light is focused unto second aperture stop
  59. 59. The use of the Lyot stop principle, plus super-polished optics, makes it possible to reject almost all of the extremely bright unwanted signal from the sun and the earth’s limb and to just see the missile signal. I worked on some space optics systems to make accurate measurements of the earth limb signal profile, as well as some wide angle reflective space-based telescopes for reconnaissance.
  60. 60. I also designed optics for medical infra-red imaging systems. The infra-red heat temperature map of a person’s face or other parts of the body can often show different kinds of illness, including cancer. There is no physical contact with the patient, just infra-red optical imaging. Display shows temperature as different colors.
  61. 61. In 1975 I changed companies again and went to work for Perkin- Elmer Corp., a maker of laboratory instruments. They were just starting to get into making some lithographic equipment. Their “Micralign” optical system made it possible to make 1.0u circuit feature sizes on 75 mm diameter silicon wafers, using mercury i-line light from a lamp. This was a 1.0 X magnification system. I designed a next generation 5X system that was able to make .50u feature sizes. The 5X magnification made the mask easier to make.
  62. 62. An ant holding 1.0 mm square chip, with tiny circuit features. What plans does the ant have for this chip? It is hard for us to imagine how small one micron really is.
  63. 63. A guitar made the same size as a red blood cell, using nanotechnology
  64. 64. nanotechnology
  65. 65. 30 years ago computer chips had circuit features one micron in size One micron
  66. 66. Today’s chips have about .03u circuit features
  67. 67. In 1976 I also worked on early experiments in Laser Fusion
  68. 68. Laser fusion, if it ever works, will be about as cost effective a way to produce energy as it is to go to the moon in order to get some sand for your children’s sandbox. It’s main use, if it works, will probably be to test the physics of new nuclear bomb designs. My work was in the very early days of laser fusion, around 1976.
  69. 69. Conic mirrorConic mirror Highly aspheric lens Target pellet Very high power laser beams enter from opposite sides and are focused onto the tiny target pellet. Laser beam Laser beam
  70. 70. Target pellet filled with tritium gas
  71. 71. Laser fusion ignition at 100 million degrees
  72. 72. Conic mirrorConic mirror Highly aspheric lens Target pellet The highly aspheric lens was made of the highest possible purity glass but it would still absorb enough of the very high power laser energy so that it would often explode! Laser beam Laser beam
  73. 73. I thought of a new type of design where there are two reflections from the mirrors instead of one, before focusing on the target pellet. The result is that the focusing lens is much thinner, with very much less asphericity and it does not explode. It is also much less expensive to make. An identical ray path is not shown here for this side of system
  74. 74. One of my first patents, in 1977, was for an unusual kind of telescope that only has spherical mirrors. Many years later one of these unusual telescopes was sent on the Cassini space craft to Saturn. Later another one went to the asteroid Vesta, and took photos.
  75. 75. This is the Cassini space craft before being launched. Another of my telescopes was on a space mission to visit a comet and fly up close to it. Close up of asteroid Vesta, taken recently from space with my telescope.
  76. 76. When my telescope on the flight to the planetoid Ceres first started showing the mysterious bright “lights” it looked for a while like we had found lights from an alien city.
  77. 77. Another telescope of my design was on the Rosetta mission to land on a comet
  78. 78. My middle years My early years
  79. 79. In 1980 I started my own one-person optical design business. This was very unusual, back in 1980 and is still not very common today in the USA. In most other countries it is very rare. It was possible for me because I had lots of business right away in lithography optics design, with some companies like Tropel, Ultra-Tech, and Perkin-Elmer. My early design work back then was done on an Apple computer, using the OSLO design program.
  80. 80. Since 1980 I have worked at home. That experience is not for everybody, but I like it.
  81. 81. 81 Salvador Dali Spanish Surrealist artist One very interesting short project I had, in 1980, was for the artist Salvador Dali.
  82. 82. Dali was once called “a genius, up to his elbow” because of his amazing technical skills, but crazy ideas – like his 1936 lobster telephone. Dali working at his desk
  83. 83. 83 Salvador Dali Late in life Dali mastered the art of making stereo pair paintings, sometimes of scenes that only existed in his amazing imagination. He wanted a novel new kind of stereo viewer to view the stereo painting pairs.
  84. 84. When I met him in 1980 Dali was an older man and not in the best shape, but his mind was tack sharp. I spent about an hour alone with him discussing stereo ideas
  85. 85. 85 Salvador Dali stereo painting pair, with about 8 distinct 3-D depth planes
  86. 86. 86 I had always been fascinated by stereo effects, like this 1957 Sears catalog ViewMaster. It was a lot of fun to work on this 3-D project for Salvador Dali.
  87. 87. Salvador Dali had managed to paint a stereo pair of paintings, which is an amazingly difficult thing to do. He wanted a new type of stereo viewer to go with his unusual painting pair. The paintings would be on a wall and then a person would look at them with a stereo viewer that could be adjusted for the viewer’s distance from the paintings.
  88. 88. 88 You just have to remember to switch the positions of the stereo paintings if you go for the alternate viewing configuration. If you don’t you get reverse stereo, which is hard on the brain.
  89. 89. Deviating prism wedges can make a stereo viewer but they have a lot of dispersive color and mapping distortion and are not adjustable. I realized that a different ray path through a prism can have no color, no distortion, and be adjustable.
  90. 90. The final viewer was just two 45-90-45 degree prisms with a flexible hinge that joined them along one prism edge. They could be folded up, when not being used, into a larger size triangle. I did not have to go anywhere near a computer to do this design project!
  91. 91. A 20” aperture Shafer-Maksutov telescope in Swansea,Wales
  92. 92. In the 1980’s both Field and Shafer independently published descriptions of a new kind of telescope. It is ideally suited for amateur telescope makers because it is very simple and inexpensive to make. There are two spherical mirrors and a single thick meniscus lens. My version has been called by others the Shafer-Maksutov. It uses the lens thickness as a more important design parameter than Ralph Field’s design version. For a large aperture telescope the lens thickness gets too large and expensive. Then a better solution is to split it into two thin lenses.
  93. 93. A retired doctor, a member of the Swansea (Wales, UK) Astronomical Society, read about my design and offered to fund the building of a 20” (500 mm) aperture telescope. The less than ideal observatory site is right on the beach. The telescope is used mostly for public education. It has recently been relocated to a better site inland.
  94. 94. Around 1990 I did the design, with a f/2.5 spherical primary mirror and about an f/18 system. The two lenses are both flat on one side and have the same convex/concave radius on the other side. BK7 glass was used, the cheapest optical glass. The design is diffraction – limited over the visual spectrum over a small field size.
  95. 95. It is the largest telescope in Wales
  96. 96. This is quite a jump up in size from the ½ meter aperture telescope in Swansea, Wales
  97. 97. Budgets will determine where this quest for ever larger telescopes will end.
  98. 98. Recently I have discovered an amazing design, of just two conic surfaces with three reflections between them. With a 100 meter diameter f/.75 primary mirror and a f/4.6 system it is diffraction-limited at .5000u over a .10 degree diameter curved field, giving a 800 mm diameter image. Both mirrors are very close to being parabolas. The obscuration due to the hole in the secondary mirror is about 8% area. The big weakness is it can’t be baffled well. f/.75 primary mirror
  99. 99. The Kilometer-Scope!! One kilometer f/1.0 primary mirror diffraction-limited f/6 system over a 4 meter diameter image
  100. 100. Just as the telescope is huge, the spectrograph is too. I did a design for it. It is unusual because the spectrograph requires an external aperture stop.
  101. 101. Because it is all-reflective it can handle the deep UV through the IR
  102. 102. Door Hole Viewer
  103. 103. Eye pupil Outside of door Door viewer optics – strong negative power gives wide field of view Extremely wide angle rays Inside of door
  104. 104. Eye outside door looking in Can’t see inside because of extreme vignetting – rays miss the eye Can only see a very narrow angle through the optics Wide angle exit pupil of door viewer is inside it, where outside eye cannot get close enough to it to be effective
  105. 105. Used by police and firemen. Also spies and voyeurs But there is a sneaky way around this!
  106. 106. Actual system Door hole viewer eye Peephole Reverse Viewer Door width
  107. 107. Hidden assumption about binoculars/monoculars • We are supposed to look through one end but not the other one • But that is what we, humans, bring to the optical device – it is not part of it Insight • You can look through it backwards too and maybe find a new use for it. You have more choices here than just the usual way of looking through it.
  108. 108. Binocular or monocular optics Unfolded light path Prisms equivalent eye eye
  109. 109. Optics used backwards eye eye Relayed image of eye
  110. 110. eye Move these optics towards right and match up its exit pupil to the pupil of door viewer. That effectively then puts eye completely to right of the door viewer, and inside the room Relayed image of eye Relayed image of eye pupil can be put inside door viewer or even outside it, inside the room eye
  111. 111. After I started my company in 1980 my optical design work has included camera lenses, medical optics, telescopes, microscopes, and many other systems. Since 1996 almost all of my work has been lithographic designs for Zeiss, in Germany, and wafer inspection designs for KLA-Tencor, in California. A typical lithographic 4X stepper lens design, from 2004. It is .80 NA, 1000mm long, has 27 lenses and 3 aspherics. The 27 mm field diameter on the fast speed end has distortion of about 1.0 nanometer, telecentricity of about 2 milliradians, and better than .005 waves r.m.s. over the field at .248u. More modern designs have more aspherics and fewer lenses.
  112. 112. These lithographic stepper lenses are made by Zeiss and then put into ASML chip- making machines.
  113. 113. These state of the art stepper lenses cost about $20 million each and many hundreds have been made by Zeiss and sent to ASML. In 2006 I invented a new type of design that combines mirrors and lenses and it is now the leading-edge Zeiss product, making today’s state of the art computer chips.
  114. 114. I have several patents on this new kind of lithographic system, that combines lenses and mirrors. Many of the lenses are aspheric, to reduce the amount of surfaces and glass volume. Some of these designs have 4 mirrors and some have 2 mirrors. One important characteristic of these designs is that there are two images inside the design, while conventional stepper lenses have no images inside the design. These are immersion designs, with a thin layer of water between the last lens surface and the silicon wafer that is being exposed. The design being made today by Zeiss is 1.35 NA and works with .193u laser light. They will not say, and I won’t either, if it looks like this design here or one of my other patents. Aspheric mirror Aspheric mirror wafer mask
  115. 115. With my latest version of this lens/mirror design and double-patterning exposures it would be possible to write a 300 X 300 spot image onto an area the size of single red blood cell – more than enough to etch a good photo of yourself, or to write an office memo, onto that surface. Red blood cells, 8u across
  116. 116. For some years I have been working for Zeiss on EUV (X-ray) lithography, which will be the next generation of lithography systems. This only uses mirrors.
  117. 117. The aspheric mirrors made for these high-performance optical systems are aligned to a precision of a few millionths of a millimeter (i.e. nanometers). Their surface figure quality (admissible deviation from the exact mathematically required surface) and the surface roughness are approximately three or four times the diameter of a hydrogen atom. (!!!!!!!)
  118. 118. 118 All-silica broadband design For KLA-Tencor I have developed new designs for wafer inspection that cover an enormous spectral region with only a single glass type. wafer .266u through .800u
  119. 119. Prototype, made by Olympus, .90 NA, wavelength = .266u - .800u
  120. 120. My future My plan is to work forever, but with fewer hours. I love optical design! After death I plan to cut back to maybe 20 hours a week.
  121. 121. My time is finished - any questions?