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5 experiments that define modern optics
5 experiments that define
modern optics
Michael Bass, Professor Emeritus
CREOL, The College of Optics and Photonics
University of Central Florida
Orlando, FL 32816-2700
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© M. Bass
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5 experiments that define modern optics
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.
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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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Thomas Young (1773-1829)
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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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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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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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The 2 slit experiment as we know it today
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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  dsinq
where q 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:
• dsinq = ml ,m = 1, 2,...
whereas the condition for destructive
interference at the screen is:
• dsinq = (m + 1/2 )l ,m = 1, 2,...
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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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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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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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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.
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•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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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 254centimeter 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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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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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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Michelson is still with us
• The LIGO interferometer:
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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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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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A sketch leaving out the great difficulties
Distant star – known position
Distant star – apparent position
Many light years
Difficulties:
Sun
1. Location
~150,000,000 km
2. Weather
3. Atmospherics
Moon
4. Angle is very
small
~400,000 km
Earth
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Arthur in the
moon’s shadow
5. Instrumentation
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The event
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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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Was it beautiful?
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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 collate
One thing at least is certain, light has
weight
One thing is certain and the rest debate
Light rays, when near the Sun, do not go
straight.
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5 experiments that define modern optics
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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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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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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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?
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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.
Pink ruby rod with
silver coatings
Laser light
Detector
Spiral flashlamp
Pulse power supply
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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
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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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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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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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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 centrosymmetric 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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5 experiments that define modern optics
The experiment (Spring 1961)
lens
Quartz crystal
Hilger and Watts quartz
prism/photographic plate
spectrograph.
A Maiman type
room temperature
ruby laser
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The data
P. A. Franken, A. E. Hill, C. W. Peters and G. Weinreich,
Phys. Rev. Letters, 7, 118 (1961)
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Optical mixing or sum frequency generation
(Fall 1961)
lens
Quartz
crystal
A Maiman type
room temperature
ruby laser
Hilger and Watts quartz
prism/photographic plate
spectrograph.
A Maiman type
The data
LN2 temperature
ruby laser
M. Bass, P. A. Franken, A. E. Hill, C. W. Peters and G.
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Weinreich, Phys. Rev. Letters, 8, 18 (1962)
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Optical rectification (Spring-summer 1962)
Rotating mirror Qswitch and supply
Photodetector
trigger
KDP
nonlinear
crystal
Oscilloscope
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M. Bass, P. A. Franken, J. F. Ward and G.
Weinreich, Phys. Rev. Letters 9, 446 (1962)
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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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5 experiments that define modern optics
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.
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