Highlights of my 51 years in optical design
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Transcript of Highlights of my 51 years in optical design
My 51 years of optical design – some highlights
Dave Shafer
David Shafer Optical Design
Fairfield, Connecticut 06824
203-259-1431
My early years
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.
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
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.
1957 Sears Roebuck catalogwhen 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
I lived on a small
farm, until I went
to college. We had
5,000 chickens.
We also had one cow, and I did not drink
pasteurized milk until I went to college.
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,
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.
A historical note here. Very soon after the telescope was invented something else was invented that did not exist before.Window shades.
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.
I devoured these three books
when I was 14 as well as the
very wonderful story of the
Mt. Palomar telescope.
I discovered for the first time, back then, that men and women see the world differently. This is still a mystery to me.
I found that men are relatively simple, with an off/on switch, but that women are more complicated. Who knew??
I was hooked on optics! When I was 15 years old
I got Conrady’s two books on lens design.
I also got a book that was
full of complicated diagrams
like this one. It made optics
look pretty difficult.
Some of this material was hard to understand but I stuck with it
I have always been able to focus my attention very well
I figured that with time I would be able to understand and communicate with math at the required level.
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.
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.
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.
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.
While at the University of Rochester I had an electrifying experience – I met my wife
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
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.
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 HeNelaser 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.
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.
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.
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.
Although computers
have revolutionized
optical design, there is
still a big need for
creative thinking by the
designer, using your
own mental PC
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.
When I was a kid I bought an AM radio
I made an unwarranted assumption
AM radio PM radio
I thought I was going to have to buy two radios.(this is a joke)
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
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.
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.
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.
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.
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.
Back to the
submarine
project.
Submarine with its periscope above the water surface
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.
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.
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.
We all know
about red eye
from camera
flash photos.
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
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
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.
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.
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.
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.
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.
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 ----
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.
With the sun behind the horizon, the earth’s limb is
ten orders of magnitude brighter than the missile’s
infra-red heat signal.
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.
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
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.
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.
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.
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.
A guitar made the same size as a red blood
cell, using nanotechnology
nanotechnology
30 years ago computer chips had circuit features one micron in size
One micron
Today’s chips have about .03u circuit features
In 1976 I also worked on early experiments in
Laser Fusion
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.
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
Target pellet
filled with
tritium gas
Laser fusion ignition
at 100 million degrees
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
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
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.
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.
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.
Another telescope of my design was on the Rosetta mission to land on a comet
My middle years
My early years
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.
Since 1980 I have worked at home. That experience is not for everybody, but I like it.
81
Salvador Dali
Spanish Surrealist artist
One very interesting
short project I had, in
1980, was for the artist
Salvador Dali.
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
Salvador DaliLate 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.
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
Salvador Dali stereo painting pair, with about 8 distinct 3-D depth planes
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.
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
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.
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.
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!
A 20” aperture Shafer-Maksutov telescope in Swansea,Wales
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.
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.
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.
It is the largest telescope in Wales
This is quite a jump up in size from the ½ meter aperture telescope in Swansea, Wales
Budgets will determine where this quest for ever larger telescopes will end.
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
The Kilometer-Scope!!
One kilometer
f/1.0 primary mirror diffraction-limited f/6 system over a 4 meter diameter image
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.
Because it is all-reflective it can handle the deep UV through the IR
Door Hole Viewer
Eyepupil
Outside of door
Door viewer optics – strong negative power gives wide field of view
Extremely wide angle rays
Inside of door
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
Used by police and firemen. Also spies and voyeurs
But there is a sneaky way around this!
Actual system Door hole viewer
eye
Peephole Reverse Viewer
Door width
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.
Binocular or monocular optics
Unfolded light path
Prisms equivalent
eye
eye
Optics used backwards
eye
eye
Relayed image of eye
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
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.
These
lithographic
stepper
lenses are
made by
Zeiss and
then put into
ASML chip-
making
machines.
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.
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
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
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.
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
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
Prototype, made by Olympus, .90 NA, wavelength = .266u - .800u
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.
My time is finished
- any questions?