5 experiments that define modern optics © m. bass 8/25/20151 5 experiments that define modern...

5 experiments that define modern optics

© M. Bass

04/19/23 1


Michael Bass, Professor EmeritusCREOL, The College of Optics and Photonics

University of Central FloridaOrlando, FL 32816-2700

© M. Bass


© M. Bass

04/19/23 2

Questions• What experiments were fundamental?

• Why were they fundamental?

• Who conceived and performed them?– What kind of people were the key players?

• What impacts did the experiments have?

My answers are my answers. Others might chose differently.


© M. Bass

04/19/23 3

The wave nature of light• Thomas Young and the double slit

interference experiment.• This is the classic example of interference

effects in light waves and • should have settled the debate between

Newton’s corpuscular theory and Huygens’ wave concepts.– Of course it would be 97 years before Planck

introduced photons or quanta of light and the problem of duality.


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04/19/23 4

Thomas Young (1773-1829)

• Thomas Young - born June 13, 1773.• Read fluently at the age of two.• Started Latin at six. • At sixteen proficient in Greek and Latin and well

acquainted with eight other languages. • By eighteen an accomplished scholar – at 19

elected to the Royal Society. • Studied medicine at Edinburgh and Göttingen.• Continued his scholarly studies at Cambridge.• When an uncle died he became financially

independent and could pursue scientific studies.


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04/19/23 5

An 1803 description• “The experiments I am about to relate ... may be repeated with

great ease, whenever the sun shines, and without any other apparatus than is at hand to every one.” – Thomas Young, November 24, 1803, Royal Society of London

• Isaac Newton's claimed light is “made of tiny bullet-like particles”, because– it is always observed to travel in straight beams, – not behavior Christian Huygens linked to wave motion.

• "...It will not be denied by the most prejudiced, that the fringes [which are observed] are produced by the interference of two portions of light.“

Thomas Young, “Experimental Demonstration of the General Law of the Interference of Light”, Philosophical Transactions of the Royal Society of London, vol 94 (1804)


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04/19/23 6

Young describes his experiment• A narrow beam of sunlight was split

with "a slip of card, about one thirtieth of an inch in breadth (thickness)."

• The slip of card was held edgewise into the sunbeam, which was made to enter the room horizontally by means of a "looking glass" (mirror) and a tiny hole in a "window shutter".

• The sunbeam had a diameter slightly greater than the thickness of the card. When the card was placed properly it split the beam into two slivers, one passing on each side of the slip of card


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04/19/23 7

The 2 slit experiment as we know it today• Two light rays pass through two slits,

separated by a distance d and strike a screen a distance, L , from the slits, as shown.

• If d < < L then the difference in path length r1 - r2 travelled by the two rays is approximately:

• r1 - r2 dsin • where is approximately equal to the

angle that the rays make relative to a perpendicular line joining the slits to the screen.

• If the rays were in phase when they passed through the slits, then the condition for constructive interference at the screen is:

• dsin = m ,m = 1, 2,... • whereas the condition for destructive

interference at the screen is: • dsin = (m + 1/2 ) ,m = 1, 2,...


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04/19/23 8

Unrecognized and then…• Young later did the classic 2 slit experiment.• His results remained obscure until 1817.• Then Augustin Fresnel rediscovered them to

confirm his theories of light.– The corpuscular theory was unacceptable.

• Young had provided a means to measure the wavelengths of light.

• This was the key to all of spectroscopy.


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04/19/23 9

The range of Young’s science• Optics

– Interference– Color theory – the first to identify the 3 color system– Measurement of wavelengths – diffraction gratings– Phase change upon reflection– Father of spectroscopy– Optics and musculature of the eye

• Mechanical properties of materials– Elastic properties of materials– Young’s Modulus

• Mechanics– First to identify mv2 with energy– First to identify Force x Distance with work

• Archeology and cryptology


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An observation• Sir Humphrey Davy said of Young,

"... Had he limited himself to any one department of knowledge, he must have been the first in that department. But as a mathematician, a scholar, a hieroglyphist, he was eminent, and he knew so much that it was difficult to say what he did not know."


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04/19/23 11

The ether and the speed of light• The Michelson interferometer and

• the Michelson-Morley experiment.

• The key to Einstein’s theory of special relativity.

• The speed of light is always the same as measured by any observer no matter his/her state of motion.


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04/19/23 12

Albert Abraham Michelson (1852-1931)

• Born - Strzelno (Poland) – Dec. 19, 1852 • Emigrated to the United States in 1855.• United States Naval Academy at 17 - did well

in science but - poorly in seamanship.• Science instructor - 1875 until 1879.• 1880 – 1882 study in Europe• 1883 Professor of Physics, Case School of

Applied Science in Cleveland– measured the speed of light to be 299,853 km s-1.

• 1889 -1892 - Professor of Physics, Clark U.• 1892-1929 - Professor and Head of the

Department of Physics at the brand new University of Chicago.

•1907 – the first American to receive the Nobel Prize in Physics.


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The early interferometer• A rather crude instrument that only sometimes

worked – prepared in Berlin 1881.– None of us can imagine how difficult it was to use.


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The next generation• If they were going to detect the earth’s motion through

the ether the interferometer had to be improved. • This one floated in a pool of mercury.


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The beam path in the Michelson-Morley Experiment


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The paper that changed history


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Comments• It is very hard to report null results.• It required great confidence and

examination of all possible alternatives.• In fact, it wasn’t until about page 4 that

they discussed the ether.• In Berlin he could see no fringes • Better instrumentation and a better light

source was needed.


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04/19/23 18

Other contributions• An international standard meter based on a cadmium

wave length. • 1878 -the speed of light using $10 worth of apparatus

along the seawall in Annapolis. • 1920 - using a 6-meter interferometer attached to a 254-

centimeter telescope, measured the diameter of the star Betelgeuse (Alpha Orionis).

• 1923 - a more accurate measurement of the speed of light - 299,798 km s-1.

• Later used a 16 km folded beam path in a vacuum tube but Michelson died shortly thereafter. In 1933 his final figure was announced as 299,774 km s-1, less than 2 km s-1 higher than the value accepted in the 1970s.


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04/19/23 19

More recognition• Albert Einstein, in 1931, publicly paid tribute to

Michelson's extensive contributions to science: "My honored Dr. Michelson, it was you who led the physicists into new paths, and through your marvelous experimental work paved the way for the development of the theory of relativity."

Albert A. Michelson, Albert Einstein and Robert A. Millikan at the Califonia Institute of Technology in 1931


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04/19/23 20

Not much of a prophet, though!• Michelson's address at the dedication ceremony

for the Ryerson Physical Laboratory at the University of Chicago in 1894:"The more important fundamental laws and

facts of physical science have all been discovered, and these are now so firmly

established that the possibility of their ever being supplanted in consequence of new discoveries is exceedingly remote.... Our

future discoveries must be looked for in the sixth place of decimals."


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04/19/23 21

Michelson is still with us• The LIGO interferometer:

American Scientist, V. 92 July-August 2004, p.355


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Gravity bends light• In 1915 Einstein predicted that light would

follow curved paths near massive objects.

• An expedition to view a total solar eclipse was considered for the fall in Russia.– This group could have tried to measure the

displacement Einstein had predicted.

• But war had broken out in August 1914.

• So we fast forward to 1919.


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04/19/23 23

Arthur Stanley Eddington (1882 -1944)• 1898 – 1902 - scholarship student at

Manchester.• Graduate work in math and physics (largest

stipend was 100 pounds per year).• Failure in studying thermionic emission -

transferred to astronomy at the Royal Observatory.

• Outstanding study of the motion of stars led to the Plumian Professor of Astronomy - Cambridge - 1913.

• 1914 - Lowndean Professor chair too and the directorship of the Cambridge Observatory.

• A Quaker - conscientious objector’s release from service in the war.


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General Relativity• In 1915 Eddington received copies of Einstein’s

and de Sitter’s papers.• He applied his mathematics background to

understanding the work and its implications.– Particularly of interest was the explanation it gave for

the precession of the perihelion of mercury.• He lectured on relativity and was described as

“together with Einstein one of the two people who understood it”.

• Eddington began to plan his test of the prediction that gravity would affect light.


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The general idea• If light is bent by a gravitating object the

source of the light will appear displaced.

• Eddington reasoned that during a total solar eclipse he could measure the position of a star seen close to the sun.

• He could then compare that position to the known position and determine if Einstein was correct.


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04/19/23 26

A sketch leaving out the great difficulties

Earth

Arthur in the moon’s shadow

Moon

Sun

Distant star – known position Distant star – apparent position

Difficulties:

1. Location

2. Weather

3. Atmospherics

4. Angle is very small

5. Instrumentation ~400,000 km

~150,000,000 km

Many light years


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04/19/23 27

The event• Sailed from England in March 1919.• Principe Island off West Africa by mid-May.• Eclipse due at 2 PM on May 29.• Eddington’s words,

– The rain stopped about noon and about 1:30 ... we began to get a glimpse of the sun. We had to carry out our photographs in faith. I did not see the eclipse, being too busy changing plates, except for one glance to make sure that it had begun and another half-way through to see how much cloud there was. We took sixteen photographs. They are all good of the sun, showing a very remarkable prominence; but the cloud has interfered with the star images. The last few photographs show a few images which I hope will give us what we need ...

• After developing the plates he noted,– ... one plate I measured gave a result agreeing with

Einstein.”


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04/19/23 28

Was it beautiful?

• An eclipse is a common and predictable event.• Measuring stellar positions is not extraordinary.• You might say it was a mundane experiment, but• its consequences were certainly dramatic.• Perhaps in its consequences it is beautiful.


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Eddington’s parody of the Rubaiyat of Omar Khayam

• Oh leave the Wise our measures to collateOne thing at least is certain, light has weightOne thing is certain and the rest debateLight rays, when near the Sun, do not go straight.


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04/19/23 30

The laser• No doubt that Charles Townes (and some

others in unpublished work) had identified the fundamental principles of the laser.– See the Townes and Shawlow paper of 1958.

• No doubt that there was a race to be the first to make a working device.

• No doubt that Theodore Maiman won the race in 1960 by flaunting convention and working on ruby.– Some claim Gordon Gould won but that is unclear.

What is, is that Gould eventually won the patent fight.


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04/19/23 31

Theodore Harold Maiman (1927 - 2007)

• Born in Los Angeles.• B.S. in engineering physics - U. of Colorado -

1949.• Ph. D. from Stanford University in 1955.• Joined the Hughes Research Laboratories in

Malibu, – Great view of the ocean.

• After the ruby laser in 1960 he left Hughes and founded Korad Laser Co. in Santa Monica.– No ocean view but less expensive rent.– Stitch joined him.

• He sold Korad to Union Carbide in 1968 and formed Maiman Associates.

• 1976 - Vice President for technology development at TRW.


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04/19/23 32

Why ruby?• Nicholas Bloembergen - three level system

– (He would get a Nobel prize for this.)• Ruby, Cr3+ ions in Al2O3 (sapphire), had been

around a long time.– It’s spectroscopy was known.– The spectroscopists at Johns Hopkins had published

values for absorption and emission coefficients.– These values said it wouldn’t work as a laser.– Maiman was certain they were wrong and Malcolm

Stitch, his boss at Hughes, let him dabble with ruby.• In fact, he did his own spectroscopic measurements to prove

his point.


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Ruby’s features• Maiman correctly chose to use “pink” or lightly

doped ruby.• It is pink because it absorbs blue and green

light.• Photographic flash lamps could produce lots of

such light to pump the levels that emitted the deep red fluorescence.

• The lifetime was ~3 msec so the lamp could pump fast enough.

• It was available and could be polished.• No one else was working on it.


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04/19/23 34

History• Henri Becquerel studied ruby fluorescence

sometime around 1900.• He noted in his record that occasionally

the red fluorescence became very narrow in wavelength.

• Years before Einstein and stimulated emission, Becquerel had seen it.

• Spectral narrowing was a sign of lasing but could not be recognized as such.


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What to look for?

• Spectral narrowing.

• Relaxation oscillations.

• Collimated beam of light.

• Threshold.


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How to do it?• Get a flashlamp, wrap it around a ruby rod and pump as hard

as you could.– Build a power supply and chamber.

• Prepare the ruby rod with plane parallel ends and silver coatings.– One 100% and one partially transmitting.

• Set up diagnostics– Your eye to see the beam.– A detector (a phototube) to monitor output waveform on an

oscilloscope.– Meters to measure input energy.

• Note – there were no laser energy/power meters, no fast solid state detectors, no electronic imaging cameras, no alignment lasers (you used an auto-collimator) and no convenient optical hardware.


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The experiment• A cleaned up sketch.

Pulse power supply

Spiral flashlamp

Pink ruby rod with silver coatings

Laser light

Detector


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04/19/23 38

Publication• After bringing in Hughes bosses to see it• and Hughes patent people to consider it,• Maiman sent a paper to Physical Review Letters.

– There was no Applied Physics Letters or J. of Quantum Electronics.

– It was sent to Bell Labs people to review and they couldn’t believe they hadn’t done it first so they rejected it.

• Maiman sent the paper to Nature where it was published.

• The dam burst!!


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A flood of lasers• Theodore Maiman at Hughes Res. Labs. - Ruby - 1960 • Ali Javan at Bell Laboratories - HeNe - 1960. • Robert Hall at IBM Watson Laboratories – Diode – 1962• Elias Snitzer at American Optical – Glass and fiber - 1961• Kumar Patel at Bell Laboratories - Carbon Dioxide -

1964. • Joseph Geusic, H. M. Marcos and L. G. Van Uitert at Bell

Laboratories – Nd:YAG – 1964• William Bridges – Hughes Research Laboratories – argon

ion - 1965• Peter Sorokin at IBM Watson Laboratories – Dye - 1966


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04/19/23 40

The start of modern nonlinear optics

• Kerr and Pockels had done nonlinear optics.– A dc field modifying an optical field is a nonlinear

effect.

• Maxwell had said let the polarization be a function of the applied field.– In an expansion this function would have nonlinear

terms.– Everyone agreed they would be too small to be

relevant.

• There had to be a horse somewhere.


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04/19/23 41

Peter Alden Franken (1929 - 1999)• Born in New York City.• Ph. D. from Columbia under

Polykarp Kusch (Nobel Laureate).• Professor of Physics at University

of Michigan – atomic physics, cross over spectroscopy and nonlinear optics.– His Ph. D. students include

Michael Bass• Director of D-ARPA.• Director of Optical Sciences Center

at University of Arizona.• Raconteur, gourmet, lover of

greyhounds.


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04/19/23 42

Second harmonic generation• Franken’s idea was that lasers made the electric field

large enough to make small terms detectable.• Weinreich pointed out that you had to have non centro-

symmetric media.• Peters had the spectrograph and the dark room.• Allan Hill was a junior year physics student with unusual

experimental skills.– While taking Franken’s undergraduate physics course Allan had

tested something in the course by a clever home experiment.– Franken thought the young man worthy of some support and

took him on as an undergraduate researcher.– Besides, no graduate students were yet available and willing to

take a risk on such a strange idea.


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The experiment (Spring 1961)

A Maiman type room temperature ruby laser

lens

Quartz crystal

Hilger and Watts quartz prism/photographic plate spectrograph.

The data

P. A. Franken, A. E. Hill, C. W. Peters and G. Weinreich, Phys. Rev. Letters, 7, 118 (1961)


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04/19/23 44

Optical mixing or sum frequency generation (Fall 1961)

A Maiman type room temperature ruby laser

lens

Hilger and Watts quartz prism/photographic plate spectrograph.

The dataA Maiman type LN2 temperature ruby laser

Quartz crystal

M. Bass, P. A. Franken, A. E. Hill, C. W. Peters and G. Weinreich, Phys. Rev. Letters, 8, 18 (1962)


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Optical rectification (Spring-summer 1962)

KDP nonlinear crystal

Oscilloscope

M. Bass, P. A. Franken, J. F. Ward and G. Weinreich, Phys. Rev. Letters 9, 446 (1962)

Rotating mirror Q-switch and supply

trigger

Photodetector


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04/19/23 46

The rest is nonlinear history• Other nonlinear properties and

phenomena were demonstrated but by others:– Stimulated Raman and Brillouin scattering– Phase matching – quasi phase matching– Third harmonics and higher – Parametric processes– etc., etc., etc.


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All of this made possible• The experiments demonstrating and

proving quantum mechanics– Alain Aspect’s brilliant demonstration of

quantum entanglement of photons.• Einstein, Podolfsky and Rosen were wrong.

• Modern spectroscopy – the alphabet soup of acronyms and Doppler free techniques.

• Photonics.


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04/19/23 48

The 5 experiments• Young’s double slit – light has wavelike

properties

• Michelson-Morely – no ether

• Eddington – light experiences gravity

• Maiman – demonstration of lasers

• Franken – demonstration of nonlinear optics

and modern optics followed.

5 experiments that define modern optics © m. bass 8/25/20151 5 experiments that define modern...

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