My 51 years of optical design – some highlights

Dave Shafer

David Shafer Optical Design

Fairfield, Connecticut 06824

shaferlens@sbcglobal.net

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. (!!!!!!!)

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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?