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Lecture 1
Phys 322
Optics
Lecture 1
Historical introduction
Optics in
Ancient History
A mirror was discovered
in workers' quarters near
the tomb of Pharaoh
Sesostris II (1900 BCE).
Pyramid of Sesostris II
(also known as
Senusret II)
Ancient Greeks (500-300 BCE)
Burning glass mentioned by Aristophanes (424 BCE)
Law of reflection: “Catoptrics” by Euclid (300 BCE)
Refraction in water mentioned by Plato in “The Republic”
But they thought that the eye emits rays that reflect off objects.
Ancient Greeks: Ancient light weapons
Early Greek and Roman
historians report that
Archimedes equipped
several hundred people
with metal mirrors to
focus sunlight onto
Roman warships in the
battle of Syracuse (213 211 BCE).
This story is probably apocryphal.
Optics in the Middle Ages: Alhazen
Arab scientist Alhazen (~1000 AD) studied spherical and
parabolic mirrors.
Alhazen correctly proposed that
the eyes passively receive light
reflected from objects, rather
than emanating light rays
themselves.
He also explained the laws
of reflection and refraction
by the slower movement of
light through denser substances.
Optics in early 17th-century Europe
Hans Lippershey applied for a
patent on the Galilean
telescope in 1608.
Galileo (1564-1642) used one
to look at our moon, Jupiter
and its moons, and the sun.
Two of Galileo’s
telescopes
Galileo’s drawings of the
moon
17th
century: optics takes off
Lecture 1
Progress in optical instrumentation:
refracting telescope, compound microscope
• 1621: Law of Refraction, Willebrord Snell
• 1664: interference: color in thin films, Robert Hooke
light is a rapid vibratory motion in media
• 1665: diffraction, Francesco Grimaldi
• 1677: wave theory, Christiaan Huygens
• 1704: particles, Isaac Newton
Newton about Newton’s rings:
"I forbore to treat of these Colors, because they seemed of a more difficult
Consideration, and were not necessary for establishing the Properties of Light
there discoursed of."
Willibrord Snell
Willibrord Snell discovered the
Law of Refraction, now named
after him.
1
n1
2
n2
ni is the refractive index of
each medium.
Willibrord Snell
(1591-1626)
n1 sin(1 )  n2 sin( 2 )
17th-century Optics
Descartes reasoned that light
must be like sound. So he
modeled light as pressure
variations in a medium
(aether).
Rene Descartes (1596-1659)
Robert Hooke (1635-1703) studied colored interference
between thin films and developed the first wave theory of
light.
Christiaan Huygens
Huygens extended the wave theory of
optics.
He realized that light slowed down on
entering dense media.
He explained polarization and
double refraction.
Double refraction
Christiaan Huygens
(1629-1695)
Huygens‘ principle
says that a wave
propagates as if
the wave-front were
composed of an array of point sources
each emitting a
spherical wave.
Isaac Newton
"I procured me a triangular glass prism
to try therewith the celebrated
phenomena of colours." (Newton,
1665)
Isaac Newton
(1642-1727)
After remaining ambivalent for many years, he eventually
concluded that it was evidence for a particle theory of light.
Particles
Isaac Newton
1643 – 1727
or
waves?
Christiaan Huygens
1629 – 1695
…18th century…
Corpuscular theory prevails
Wave theory is forgotten…
19th century
• 1801: interference, Thomas Young
famous double-slit experiment
color in thin films
diffraction of light
diffraction grating:
"These colors may be easily seen, in an irregular form, by looking at any
metal, coarsely polished, in the sunshine; but they become more distinct and
conspicuous, when a number of fine lines of equal strength are drawn
parallel to each other, so as to conspire in their effects."
• 1814, Frensel ‘rediscovers’
interference and diffraction
James Clerk Maxwell
Maxwell unified electricity and
magnetism with his now famous
equations and showed that light is an
electromagnetic wave.
 
E  0
 
B  0

 
B
 E  
t

  1 E
 B  2
c t
James Clerk
Maxwell (18311879)


where E is the electric field, B is the magnetic field, and c
is the velocity of light.
Maxwell’s equations simplify to the wave
equation for the electric field.

 1  E
2
 E 2
0
2
c t
2
which has a simple sine-wave solution:
 
 
E (r , t )  cos(t  k  r )
where

c / k
The same is true for the magnetic field.
19th century: Maxwell
~1864:
Maxwell introduced four
equations that described all known
electro-magnetic phenomena and
showed theoretically that
electromagnetic pulse or wave
moving in space could exist.
Surprisingly, he found that this EMwave must move at a speed of
300,000 km/s - i.e. speed of light!
Maxwell suggested that
light is electromagnetic wave
Maxwell’s equations
 E   E A 
q
0
 B   B A  0
 B
E   E||l  
t
 E 

 B||l  0  I   0 t 
Light is an electromagnetic wave.
The electric (E) and magnetic (B) fields are in phase.
The electric field, the magnetic field, and the propagation
direction are all perpendicular.
19th century: Hertz
In 1886 Heinrich Hertz experimentally proved the
electromagnetic wave nature of light
"It's of no use whatsoever,“
"This is just an experiment that proves Maestro Maxwell was
right - we just have these mysterious electromagnetic waves
that we cannot see with the naked eye. But they are there.“
EM wave transmitter
1857 - 1894
EM wave receiver
Michelson & Morley
Michelson and Morley then
attempted to measure the earth's
velocity with respect to the
aether and found it to be zero,
effectively disproving the
existence of the aether.
Albert
Edward
Michelson
Morley
(1852-1931) (1838-1923)
20th century
Difficulties:
Wave theory cannot explain:
- black body radiation spectrum
- photoelectric effect
- speed of light measured by two detectors moving in respect to
each other is exactly the same…
20th century: The birth of quantum theory
1900: To explain black body radiation, Planck
suggested that energy of light consists of quanta
Ephoton = h
Planck’s constant
frequency
Max Karl Ernst
Ludwig Planck
1905: Albert Einstein proposed that light consists
of particles (photons) that have energy and
momentum depending on frequency
Special theory of relativity: speed of light in
vacuum is the same in all inertial reference systems
20th century: quantum theory
Quantum nature of light is pronounced at low light intensities
Light: dual nature, both wave and particle
In this course, we will mostly work in the frame of classical
EM wave theory of light
Albert Einstein
Einstein showed that light:
is a phenomenon of empty space;
has a velocity that’s constant,
independent of observer velocity;
is both a wave and a particle;
Albert Einstein (1879-1955)
Excited medium
and undergoes stimulated
emission, the basis of the
laser.