Forgotten milestones in the history of optics

1
Forgotten milestones in the history of optics

• Greg Gbur
• Department of Physics and Optical Science
• UNC Charlotte

2
Introduction

• History is important!
• A proper study of historical experiments can give
  crucial context, and understanding
• Many important and enlightening experiments have
  been forgotten by science
• An understanding of such experiments can provide
  inspiration and a better understanding of the
  philosophy of science

3
Periods of optical history

• Prehistory initial studies of optics and vision
• Particle light treated as a stream of particles
• Wave light treated as a continuous wave
• Quantum light has wave/particle duality
• Modern light even weirder than we imagined!

4
Periods of optical history

• Prehistory Aristotle, Ptolemy, Ibn al-Haytham
• Particle Newton published Optiks in 1704
• Wave Young published double slit experiment in
  1803
• Quantum Einstein published photoelectric effect
  in 1905
• Modern Maiman builds first laser in 1960

5
Periods of optical history

• Prehistory Ibn al-Haytham writes Book of Optics
  between 1011-1021 C.E.
• Particle/Wave François Arago studies stellar
  aberration in 1810
• Wave/Quantum Charles Barkla shows that X-rays
  have polarization in 1905
• Modern Leonard Mandel shows multi-photon
  interference in 1963

6
Prehistory of optics

• Earliest scientific studies of light could be
  attributed to Aristotle, Ptolemy, Euclid
• Light and vision were concepts essentially
  independent (but intertwined)

Aristotle (384-322 B.C.E.)
Euclid (c. 300 B.C.E.)
Ptolemy (90-168 C.E.)
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Models of vision
Adapted from Bradley Steffens, Ibn al-Haytham,
First Scientist (Morgan Reynolds, Greensboro, NC,
2007), as is much of the discussion of
al-Haytham. A great HS-level introduction to Ibn
al-Haytham, and the only popular biography I know
of.
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Ibn al-Haytham (965-1039 C.E.)

• born in Basra (Iraq), devoted his early life to
  theology, but grew frustrated with sectarian
  arguments
• Discovered the works of Aristotle as a young
  man, and devoted his life to the study of the
  physical world
• Studied, and eventually commented on, works of
  Aristotle, Euclid, Archimedes, Ptolemy

(from Iraqi 10 dinar note)

• Appointed a vizier in the Basra government, but
  was dismissed from the job by either feigned or
  actual mental illness
• Wrote possibly more than 200 works, with some 50
  still surviving in some form
• Provided the first description of a scientific
  method
• Studied optics, astronomy, geometry, mechanics,
  water clocks, medicine, anatomy, business
  arithmetic, even civil engineering!

9
Islamic Renaissance

• Muslim scholars carefully studied the works of
  ancient Greeks (Aristotle, Plato, Archimedes,
  Euclid, Ptolemy) and many translations existed
• caliph Abu Jafar al-Mamun ibn Harun of Iraq
  founded the Bait-ul-Hikmat (House of Wisdom)
  around 813 C.E., in Baghdad
• In 825, Muhammed ibn Musa al-Khwarizmi adopted
  Arabic numerals from Hindu mathematicians
• al-Khwarizmi also introduced algebra to the
  Muslim world (al-jabr)

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Ibn al-Haytham in Cairo

• Called to Cairo around 1010 C.E. by The Mad
  Caliph al-Hakim, to attempt to dam the Nile!
• Project was determined to be infeasible
• Seems to have been given a government post
  nevertheless (though accounts vary)

Aswan high dam

• Soon after, mental illness came back or he
  began faking it in order to get out of government
  duties! (like modern-day jury duty?)
• Was placed under house arrest in Cairo for a
  period of ten years, deprived of his belongings
• It seems that during this period he developed
  his Book of Optics!

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al-Haythams Book of Optics

• Seven-volume book on vision, the anatomy of the
  eye, light propagation, reflection, and
  refraction
• Introduces rectilinear propagation of light
  light travels in straight lines from object to
  eye
• Sight does not perceive any visible object
  unless there exists in the object some light,
  which the object possesses of itself or which
  radiates upon it from another object

• First to make the (seemingly obvious) connection
  between light and vision
• First to observe that the brain is the center of
  vision, not the eye
• Introduced the distinction between primary and
  secondary sources
• Performed the first non-trivial demonstration of
  the camera obscura

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Camera obscura
Using geometrical optics, we can demonstrate that
light passing through a small pinhole into a
darkened room forms a reversed image of the
object
Naturalists prior to al-Haytham had observed this
type of effect via, for instance, sunlight
traveling through gaps in the leaves, but none
apparently had studied the phenomena
systematically
13
Ibn al-Haythams Camera obscura
Ibn al-Haytham used multiple light sources to
demonstrate that light followed straight line
paths through the holes
By screening one light source or another, was
able to demonstrate that the image was inverted
on passing through the hole!
14
Ibn al-Haytham conclusions

• Experiment was not done to demonstrate imaging,
  but rather the non-interaction of light rays with
  one another
• all the lights that appear in the dark place
  have reached it through the aperture alone
  therefore the lights of all those lamps have come
  together at the aperture, then separated after
  passing through it. Thus, if lights blended in
  the atmosphere, the lights of the lamps meeting
  at the aperture would have mixed in the air at
  the aperture and they would have come out so
  mingled together that they would not be
  subsequently distinguishable. We do not,
  however, find the matter to be so rather the
  lights are found to come out separately, each
  being the opposite the lamp from which it has
  arrived.

15
al-Haythams influence

• al-Haythams Book of Optics remained one of the
  most influential optics books throughout the
  prehistory period
• translated into Latin al-Haytham Latinized to
  Alhazen or Alhacen
• influenced significant medieval optical
  researchers such as Roger Bacon (1214-1294)

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Corpuscular era of light

• By late 1600s, basics of geometrical optics had
  been established (Snells law in 1621, Fermats
  principle of least time in 1662)
• In 1690, Christiaan Huygens published Traité de
  la Lumière, suggesting light is a wave phenomenon
• Newtons 1704 Optiks, however, firmly cemented
  the corpuscular (particle) theory of light for
  100 years

17
Transition to the wave era

• In 1803, Thomas Young published his famous
  double slit experiment demonstrating the wave
  nature of light however, the result was not
  immediately recognized
• An explanation of diffraction was proposed as the
  subject of the 1818 Paris Academy prize question
• Augustin Jean Fresnel explained diffraction based
  on a wave theory of light
• Poisson argued against it, stating that the
  theory would lead to a bright spot behind an
  opaque disk Arago experimentally found the spot!
  (Arago spot)

18
François Arago (1786-1853)

• A French physicist, mathematician, astronomer,
  politician and unwilling adventurer!
• Made fundamental contributions to optics the
  Arago spot, the Fresnel-Arago laws, and the
  stellar aberrations to be mentioned, among others
• After 1830s, was an active liberal republican
  in French politics, and his influence and
  guidance helped spur many scientific discoveries

• In 1806, went to Spain to perform meridional
  measurements in June 1808, he was accused as a
  spy and imprisoned in a fortress in July 1808 he
  escaped in a fishing boat, reaching Algiers in
  August. Mid-August, sailing to France, his ship
  was captured by a Spanish corsair, and he was
  imprisoned in Spain until November! Freed, his
  next trip to Marseilles was blown back by a bad
  wind to the coast of Africa, at which point he
  took a six month trip back to Algiers on land.
  Finally sailing to Marseilles, he was quarantined
  for some time!

19
The speed of light

• Measurements of the speed of light had first been
  made by Römer in 1676

Essentially the Doppler effect!
20
Stellar aberration
The combination of the finite speed of light and
the motion of the earth leads to stellar
aberration, a phenomenon in which starlight
appears to come from different directions at
different times of year (first observed in 1725
by James Bradley)
21
Stellar aberration

• Aberration angle tan? v/c
• Can in principle use stellar aberration to
  measure the speed of light
• Researchers of the time were interested in
  measuring variations in the speed of light
• Heavier stars were expected to produce slower
  light in the corpuscular theory
• Stellar aberration alone not precise enough to
  measure difference

22
Newtonian view of refraction
According to Newtonian theory of refraction,
light particles refract because they speed up in
matter i.e., speed c becomes speed nc
To reproduce Snells law (with n2 n), must have
23
Aragos experiment (1810)
Arago realized that light traveling at different
initial speeds should be refracted at different
angles
same direction of incidence
refraction of light 1
refraction of light 2
refraction angles different!
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Results

• Arago found that the light from every star is
  refracted by the same amount!
• This result seems to be, with the first aspect,
  in manifest contradiction with the Newtonian
  theory of the refraction, since a real inequality
  in the speed of the rays however does not cause
  any inequality in the deviations which they test.
  It even seems that one can return of it reason
  only by supposing that the luminous elements emit
  rays with all kinds speeds, provided that it is
  also admitted that these rays are visible only
  when their speeds lie between given limits. On
  this assumption, indeed, the visibility of the
  rays will depend their relative speeds, and, as
  these same speeds determine the quantity of the
  refraction, the visible rays will be always also
  refracted.

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Conclusions and impact

• Newtons particle theory of light completely
  failed to explain Aragos experiment a wave
  theory of light seemed the only possibility
• In 1818, Fresnel suggested that the aether, the
  hypothetical medium in which light travels, is
  partially dragged along with a material medium
• Result led Arago to embrace the wave theory of
  light, and also led to widespread belief in the
  aether!
• (True explanation of Aragos results in special
  relativity)
• A failed experiment, based on incorrect theories
  of light propagation, interpreted incorrectly by
  Fresnel, but which helped convince people of the
  (correct) wavelike properties of light!

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The wave era of light

• Fresnel and Arago (1816) showed that orthogonal
  polarizations would not interfere
• Young (1817) interpreted light as a transverse
  wave
• Ørsted, Ampère (1820) and Faraday (1831) showed
  that electricity and magnetism are related
• Maxwell (1864) laid the theoretical foundations
  for light as an electromagnetic wave
• Hertz (1887) experimentally demonstrated
  electromagnetic waves

27
X-rays

• In 1895, Wilhelm Conrad Röntgen discovered a
  mysterious new form of radiation, by accident,
  dubbed X-rays
• After two short weeks of experiments, the first
  X-ray photograph was produced of the human body,
  using his wife Anna as a test subject

Rays produced when high-energy electrons collide
with an anticathode in a cathode ray tube this
one is a Cossor tube
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Are X-rays electromagnetic waves?
Physical origin of X-rays was not immediately
clear. Were they a new form of particle? A new
form of wave? Or another manifestation of
electromagnetic waves? Three properties of X-rays
seemed very unlike light and other E/M radiation

• X-rays did not seem to be refracted when
  entering a material surface
• X-rays are reflected diffusely at a surface,
  instead of being reflected in a single direction
  (specular reflection)
• X-rays did not seem to experience diffraction

29
Charles Glover Barkla (1877-1944)

• British physicist who worked as a professor of
  natural philosophy at the University of Edinburgh
  from 1917 until his death
• Ph.D. advisors were J.J. Thomson, discoverer of
  the electron, and O. Lodge, a key developer of
  wireless telegraphy

• Worked primarily in X-ray scattering, X-ray
  spectroscopy, and the excitation of secondary
  X-rays
• Won the Nobel Prize in 1917 for his discovery
  of the characteristic X-radiation of the
  elements.

30
Wilberforces idea (I)
Polarization would be a good indication of the
electromagnetic nature of X-rays however,
ordinary methods of polarizing light do not work
for X-rays they shoot right through polarizers,
and because they dont specularly reflect
Brewsters angle doesnt work. Researchers knew
that X-rays passing through gas scatter and
produce secondary X-rays
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Wilberforces idea (II)
Professor Wilberforce suggested to Barkla that
one could use the secondary radiation as a
polarized source, and scattering the secondary
radiation, produce a tertiary beam of radiation,
which should have a dipole behavior
Unfortunately, secondary radiation is weak
tertiary radiation is negligible!
32
Barklas experiment (1905)
Barkla realized, however, that polarized X-rays
must be produced right at the anticathode
An appropriately-collimated beam of radiation
from the anticathode could be scattered from a
gas, and the secondary radiation would have
polarization properties!
33
Barklas experiment (II)
Rotation of the bulb should result in the
secondary radiation appearing in the vertical
position, for horizontal rays, or the horizontal
position, for vertical rays
34
Barklas results
As the bulb was rotated round the axis of the
primary beam there was, of course, no change in
the intensity of primary radiation in that
direction.  There was, however, a considerable
change in the intensity of secondary radiation in
both the horizontal and vertical directions, one
reaching a maximum when the other attained a
minimum.   By turning the bulb through a right
angle the electroscope which had previously
indicated a maximum of intensity indicated a
minimum, and vice versa.  The position of the
bulb when the vertical secondary beam attained a
maximum of intensity and the horizontal secondary
beam a minimum was that in which the kathode
stream was horizontal, the maximum and minimum
being reversed when the kathode stream was
vertical.  By turning the bulb through another
right angle, so that the kathode stream was again
horizontal but in the opposite direction to that
in the other horizontal position, the maximum and
minimum were attained as before.
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Quantum era of light

• The same year of Barklas publication (1905),
  Einstein developed special relativity and
  explained the photoelectric effect by
  (re)postulating the particle nature of light
• Quantum mechanics was developed rapidly to
  explain atomic structure and the nature of the
  light/matter interaction
• Detailed studies of the behavior of light
  particles (photons) was somewhat hindered by the
  lack of a quality light source

36
Paul Diracs (in)famous statement
In his 1930 text Principles of Quantum Mechanics,
the brilliant scientist Paul Dirac made the
following statement
Some time before the discovery of quantum
mechanics people realized that the connexion
between light waves and photons must be of a
statistical character. What they did not clearly
realize, however, was that the wave function
gives information about the probability of one
photon being in a particular place and not the
probable number of photons in that place. The
importance of the distinction can be made clear
in the following way. Suppose we have a beam of
light consisting of a large number of photons
split up into two components of equal intensity.
On the assumption that the intensity of a beam is
connected with the probable number of photons in
it, we should have half the total number of
photons going into each component. If the two
components are now made to interfere, we should
require a photon in one component to be able to
interfere with one in the other. Sometimes these
two photons would have to annihilate one another
and other times they would have to produce four
photons. This would contradict the conservation
of energy. The new theory, which connects the
wave function with probabilities for one photon,
gets over the difficulty by making each photon go
partly into each of the two components. Each
photon then interferes only with itself.
Interference between two different photons never
occurs.
37
Quantum to modern era

• In 1917, Einstein established the theoretical
  foundations of stimulated emission
• In 1953, Charles H. Townes and students produced
  the first microwave amplifier based on this
  principle (the first MASER was built in Russia at
  a similar time, by Basov and Prokhorov)
• Theodore H. Maiman produced the first working
  LASER in 1960
• Basov, Prokhorov and Townes shared the 1964 Nobel
  Prize in Physics

38
Leonard Mandel (1927-2001)

• Born in Berlin, Germany
• Earned his Ph.D. in nuclear physics from
  Birkbeck College, University of London, in 1951
• One of the pioneers of the field of quantum
  optics, which has led to such speculative ideas
  as quantum computing, quantum cryptography, and
  quantum teleportation (and he had a hand in all
  of them) and tested the foundations of quantum
  mechanics itself

• Became a faculty member at the Institute of
  Optics at the University of Rochester in 1964, at
  the invitation of colleague Professor Emil Wolf

39
Interference of independent beams

• Interference requires, in essence, that the wave
  fields being interfered have a definite phase
  relationship with respect to each other
• Two independent lasers will fluctuate
  independently of one another and on average will
  produce no discernable interference pattern
• Note the clause on average is the absence of
  interference just an artifact of the averaging
  process, or a true manifestation of Diracs
  statement, Interference between two different
  photons never occurs?

40
Interference of independent beams
Classically, two quasi-monochromatic waves will
stay in phase for a finite period of time during
that time, it should be possible to see an
interference pattern between them
41
Magyar and Mandels experiment (1963)
Two light beams from two independent ruby masers
are aligned with the help of two adjustable 45º
mirrors and superposed on the photocathode of an
electronically gated image tube.  The tube is
magnetically focused and the image produced on
the output fluorescent screen is photographed.
42
MM results
Fringes were observed, as can be seen both in the
photocathode image (left) and the microphotometer
tracing on the right
So it would seem that different photons can
interfere with one another, violating Diracs
original statement or can they?
43
The quantum plot thickens

• In 1967, L. Mandel and R.L. Pfleegor would repeat
  the experiment with very low intensity light
  sources
• With high probability, only one photon is present
  at the detector at any time
• They still found an interference pattern!
• Surprising as it might seem, the statement of
  Dirac quoted in the introduction appears to be as
  appropriate in the context of this experiment as
  under the more usual conditions of
  interferometry.
• (I would say that Diracs statement is
  appropriate, but not a terribly useful one in the
  context of this experiment)

44
A Meta era of optics?
Recent discoveries have shifted the focus of
optics from, What is the behavior of light? to,
How can we make light behave how we want it to?

• T.W. Ebbesen, H.J. Lezec, H.F. Ghaemi, T. Thio,
  and P.A. Wolff, Extraordinary optical
  transmission through sub-wavelength hole arrays,
  Nature 391 (1998), 667.
• J.B. Pendry, Negative Refraction Makes a
  Perfect Lens, Phys. Rev. Lett. 85 (2000), 3966.
• U. Leonhardt, Optical Conformal Mapping,
  Science 312 (2006), 1777.
• J. B. Pendry, D. Schurig, D. R. Smith,
  Controlling electromagnetic fields, Science 312
  (2006), 1780.

45
Investigating the history of optics
Pretty much any historical paper, from 1600s
through the 1930s, can be found freely available
on Google books and through other sources!

• Bradley Steffens, Ibn al-Haytham, First
  Scientist (Morgan Reynolds, Greensboro, NC, 2007)
• François Arago, Œuvres Complètes, Tome 7, Volume
  4 (1858), p. 548-568.
• Charles Barkla, Polarisation in Röntgen rays,
  Nature 69 (1904), 463.
• Charles Barkla, Polarized Röntgen radiation,
  Phil. Trans. Roy. Soc. Lond. A 204 (1905), 467.
• G. Magyar and L. Mandel, Interference fringes
  produced by superposition of two independent
  maser light beams, Nature 198 (1963), 255.
• R.Pfleegor and L. Mandel, Interference of
  independent photon beams, Phys. Rev. 159 (1967),
  1084.