is the branch of physics which involves the behaviour and
properties of light, including its interactions with matter and the
construction of instruments that use or detect it.
describes the behaviour of visible, ultraviolet, and infrared light.
Because light is an electromagnetic wave, other forms of
electromagnetic radiation such as X-rays, microwaves, and radio waves
exhibit similar properties.
Most optical phenomena can be accounted for using the classical
electromagnetic description of light. Complete electromagnetic
descriptions of light are, however, often difficult to apply in
practice. Practical optics is usually done using simplified models.
The most common of these, geometric optics, treats light as a
collection of rays that travel in straight lines and bend when they
pass through or reflect from surfaces.
is a more
comprehensive model of light, which includes wave effects such as
diffraction and interference that cannot be accounted for in geometric
optics. Historically, the ray-based model of light was developed
first, followed by the wave model of light. Progress in
electromagnetic theory in the 19th century led to the discovery that
light waves were in fact electromagnetic radiation.
Some phenomena depend on the fact that light has both wave-like and
particle-like properties. Explanation of these effects requires
quantum mechanics. When considering light's particle-like properties,
the light is modelled as a collection of particles called "photons".
deals with the application of quantum mechanics to
Optical science is relevant to and studied in many related disciplines
including astronomy, various engineering fields, photography, and
medicine (particularly ophthalmology and optometry). Practical
applications of optics are found in a variety of technologies and
everyday objects, including mirrors, lenses, telescopes, microscopes,
lasers, and fibre optics.
2 Classical optics
2.1 Geometrical optics
2.2 Physical optics
2.2.1 Modelling and design of optical systems using physical optics
2.2.2 Superposition and interference
Diffraction and optical resolution
2.2.4 Dispersion and scattering
18.104.22.168 Changing polarization
22.214.171.124 Natural light
3 Modern optics
3.2 Kapitsa–Dirac effect
4.1 Human eye
4.1.1 Visual effects
4.1.2 Optical instruments
4.3 Atmospheric optics
5 See also
7 External links
Main article: History of optics
See also: Timeline of electromagnetism and classical optics
The Nimrud lens
Optics began with the development of lenses by the ancient Egyptians
and Mesopotamians. The earliest known lenses, made from polished
crystal, often quartz, date from as early as 700 BC for Assyrian
lenses such as the Layard/Nimrud lens. The ancient Romans and
Greeks filled glass spheres with water to make lenses. These practical
developments were followed by the development of theories of light and
vision by ancient Greek and Indian philosophers, and the development
of geometrical optics in the Greco-Roman world. The word optics comes
from the ancient Greek word ὀπτική (optikē), meaning
Greek philosophy on optics broke down into two opposing theories on
how vision worked, the "intromission theory" and the "emission
theory". The intro-mission approach saw vision as coming from
objects casting off copies of themselves (called eidola) that were
captured by the eye. With many propagators including Democritus,
Aristotle and their followers, this theory seems to have
some contact with modern theories of what vision really is, but it
remained only speculation lacking any experimental foundation.
Plato first articulated the emission theory, the idea that visual
perception is accomplished by rays emitted by the eyes. He also
commented on the parity reversal of mirrors in Timaeus. Some
hundred years later,
Euclid wrote a treatise entitled
Optics where he
linked vision to geometry, creating geometrical optics. He based
his work on Plato's emission theory wherein he described the
mathematical rules of perspective and described the effects of
refraction qualitatively, although he questioned that a beam of light
from the eye could instantaneously light up the stars every time
someone blinked. Ptolemy, in his treatise Optics, held an
extramission-intromission theory of vision: the rays (or flux) from
the eye formed a cone, the vertex being within the eye, and the base
defining the visual field. The rays were sensitive, and conveyed
information back to the observer’s intellect about the distance and
orientation of surfaces. He summarised much of
Euclid and went on to
describe a way to measure the angle of refraction, though he failed to
notice the empirical relationship between it and the angle of
Alhazen (Ibn al-Haytham), "the father of Optics"
Reproduction of a page of Ibn Sahl's manuscript showing his knowledge
of the law of refraction.
During the Middle Ages, Greek ideas about optics were resurrected and
extended by writers in the Muslim world. One of the earliest of these
Al-Kindi (c. 801–73) who wrote on the merits of Aristotelian and
Euclidean ideas of optics, favouring the emission theory since it
could better quantify optical phenomena. In 984, the Persian
mathematician Ibn Sahl wrote the treatise "On burning mirrors and
lenses", correctly describing a law of refraction equivalent to
Snell's law. He used this law to compute optimum shapes for lenses
and curved mirrors. In the early 11th century,
al-Haytham) wrote the
Book of Optics
Book of Optics (Kitab al-manazir) in which he
explored reflection and refraction and proposed a new system for
explaining vision and light based on observation and
experiment. He rejected the "emission theory" of
Ptolemaic optics with its rays being emitted by the eye, and instead
put forward the idea that light reflected in all directions in
straight lines from all points of the objects being viewed and then
entered the eye, although he was unable to correctly explain how the
eye captured the rays. Alhazen's work was largely ignored in the
Arabic world but it was anonymously translated into Latin around 1200
A.D. and further summarised and expanded on by the Polish monk
Witelo making it a standard text on optics in Europe for the next
In the 13th century in medieval Europe, English bishop Robert
Grosseteste wrote on a wide range of scientific topics, and discussed
light from four different perspectives: an epistemology of light, a
metaphysics or cosmogony of light, an etiology or physics of light,
and a theology of light, basing it on the works
Platonism. Grosseteste's most famous disciple, Roger Bacon, wrote
works citing a wide range of recently translated optical and
philosophical works, including those of Alhazen, Aristotle, Avicenna,
Averroes, Euclid, al-Kindi, Ptolemy, Tideus, and Constantine the
African. Bacon was able to use parts of glass spheres as magnifying
glasses to demonstrate that light reflects from objects rather than
being released from them.
The first wearable eyeglasses were invented in Italy around 1286.
This was the start of the optical industry of grinding and polishing
lenses for these "spectacles", first in Venice and Florence in the
thirteenth century, and later in the spectacle making centres in
both the Netherlands and Germany. Spectacle makers created
improved types of lenses for the correction of vision based more on
empirical knowledge gained from observing the effects of the lenses
rather than using the rudimentary optical theory of the day (theory
which for the most part could not even adequately explain how
spectacles worked). This practical development, mastery, and
experimentation with lenses led directly to the invention of the
compound optical microscope around 1595, and the refracting telescope
in 1608, both of which appeared in the spectacle making centres in the
In the early 17th century
Johannes Kepler expanded on geometric optics
in his writings, covering lenses, reflection by flat and curved
mirrors, the principles of pinhole cameras, inverse-square law
governing the intensity of light, and the optical explanations of
astronomical phenomena such as lunar and solar eclipses and
astronomical parallax. He was also able to correctly deduce the role
of the retina as the actual organ that recorded images, finally being
able to scientifically quantify the effects of different types of
lenses that spectacle makers had been observing over the previous 300
years. After the invention of the telescope Kepler set out the
theoretical basis on how they worked and described an improved
version, known as the Keplerian telescope, using two convex lenses to
produce higher magnification.
Cover of the first edition of Newton's Opticks
Optical theory progressed in the mid-17th century with treatises
written by philosopher René Descartes, which explained a variety of
optical phenomena including reflection and refraction by assuming that
light was emitted by objects which produced it. This differed
substantively from the ancient Greek emission theory. In the late
1660s and early 1670s,
Isaac Newton expanded Descartes' ideas into a
corpuscle theory of light, famously determining that white light was a
mix of colours which can be separated into its component parts with a
prism. In 1690,
Christiaan Huygens proposed a wave theory for light
based on suggestions that had been made by
Robert Hooke in 1664. Hooke
himself publicly criticised Newton's theories of light and the feud
between the two lasted until Hooke's death. In 1704, Newton published
Opticks and, at the time, partly because of his success in other areas
of physics, he was generally considered to be the victor in the debate
over the nature of light.
Newtonian optics was generally accepted until the early 19th century
when Thomas Young and
Augustin-Jean Fresnel conducted experiments on
the interference of light that firmly established light's wave nature.
Young's famous double slit experiment showed that light followed the
law of superposition, which is a wave-like property not predicted by
Newton's corpuscle theory. This work led to a theory of diffraction
for light and opened an entire area of study in physical optics.
Wave optics was successfully unified with electromagnetic theory by
James Clerk Maxwell
James Clerk Maxwell in the 1860s.
The next development in optical theory came in 1899 when Max Planck
correctly modelled blackbody radiation by assuming that the exchange
of energy between light and matter only occurred in discrete amounts
he called quanta. In 1905
Albert Einstein published the theory of
the photoelectric effect that firmly established the quantization of
light itself. In 1913
Niels Bohr showed that atoms could only
emit discrete amounts of energy, thus explaining the discrete lines
seen in emission and absorption spectra. The understanding of the
interaction between light and matter which followed from these
developments not only formed the basis of quantum optics but also was
crucial for the development of quantum mechanics as a whole. The
ultimate culmination, the theory of quantum electrodynamics, explains
all optics and electromagnetic processes in general as the result of
the exchange of real and virtual photons.
Quantum optics gained practical importance with the inventions of the
maser in 1953 and of the laser in 1960. Following the work of Paul
Dirac in quantum field theory, George Sudarshan, Roy J. Glauber, and
Leonard Mandel applied quantum theory to the electromagnetic field in
the 1950s and 1960s to gain a more detailed understanding of
photodetection and the statistics of light.
Classical optics is divided into two main branches: geometrical (or
ray) optics and physical (or wave) optics. In geometrical optics,
light is considered to travel in straight lines, while in physical
optics, light is considered as an electromagnetic wave.
Geometrical optics can be viewed as an approximation of physical
optics that applies when the wavelength of the light used is much
smaller than the size of the optical elements in the system being
Main article: Geometrical optics
Geometry of reflection and refraction of light rays
Geometrical optics, or ray optics, describes the propagation of light
in terms of "rays" which travel in straight lines, and whose paths are
governed by the laws of reflection and refraction at interfaces
between different media. These laws were discovered empirically as
far back as 984 AD and have been used in the design of optical
components and instruments from then until the present day. They can
be summarised as follows:
When a ray of light hits the boundary between two transparent
materials, it is divided into a reflected and a refracted ray.
The law of reflection says that the reflected ray lies in the plane of
incidence, and the angle of reflection equals the angle of incidence.
The law of refraction says that the refracted ray lies in the plane of
incidence, and the sine of the angle of refraction divided by the sine
of the angle of incidence is a constant:
displaystyle frac sin theta _ 1 sin theta _ 2 =n
where n is a constant for any two materials and a given colour of
light. If the first material is air or vacuum, n is the refractive
index of the second material.
The laws of reflection and refraction can be derived from Fermat's
principle which states that the path taken between two points by a ray
of light is the path that can be traversed in the least time.
Geometric optics is often simplified by making the paraxial
approximation, or "small angle approximation". The mathematical
behaviour then becomes linear, allowing optical components and systems
to be described by simple matrices. This leads to the techniques of
Gaussian optics and paraxial ray tracing, which are used to find basic
properties of optical systems, such as approximate image and object
positions and magnifications.
Main article: Reflection (physics)
Diagram of specular reflection
Reflections can be divided into two types: specular reflection and
Specular reflection describes the gloss of
surfaces such as mirrors, which reflect light in a simple, predictable
way. This allows for production of reflected images that can be
associated with an actual (real) or extrapolated (virtual) location in
Diffuse reflection describes non-glossy materials, such as
paper or rock. The reflections from these surfaces can only be
described statistically, with the exact distribution of the reflected
light depending on the microscopic structure of the material. Many
diffuse reflectors are described or can be approximated by Lambert's
cosine law, which describes surfaces that have equal luminance when
viewed from any angle. Glossy surfaces can give both specular and
In specular reflection, the direction of the reflected ray is
determined by the angle the incident ray makes with the surface
normal, a line perpendicular to the surface at the point where the ray
hits. The incident and reflected rays and the normal lie in a single
plane, and the angle between the reflected ray and the surface normal
is the same as that between the incident ray and the normal. This
is known as the Law of Reflection.
For flat mirrors, the law of reflection implies that images of objects
are upright and the same distance behind the mirror as the objects are
in front of the mirror. The image size is the same as the object size.
The law also implies that mirror images are parity inverted, which we
perceive as a left-right inversion. Images formed from reflection in
two (or any even number of) mirrors are not parity inverted. Corner
reflectors retroreflect light, producing reflected rays that
travel back in the direction from which the incident rays came.
Mirrors with curved surfaces can be modelled by ray tracing and using
the law of reflection at each point on the surface. For mirrors with
parabolic surfaces, parallel rays incident on the mirror produce
reflected rays that converge at a common focus. Other curved surfaces
may also focus light, but with aberrations due to the diverging shape
causing the focus to be smeared out in space. In particular, spherical
mirrors exhibit spherical aberration. Curved mirrors can form images
with magnification greater than or less than one, and the
magnification can be negative, indicating that the image is inverted.
An upright image formed by reflection in a mirror is always virtual,
while an inverted image is real and can be projected onto a
Main article: Refraction
Snell's Law for the case n1 < n2, such as air/water
Refraction occurs when light travels through an area of space that has
a changing index of refraction; this principle allows for lenses and
the focusing of light. The simplest case of refraction occurs when
there is an interface between a uniform medium with index of
displaystyle n_ 1
and another medium with index of refraction
displaystyle n_ 2
. In such situations,
Snell's Law describes the resulting deflection
of the light ray:
displaystyle n_ 1 sin theta _ 1 =n_ 2 sin theta _ 2
displaystyle theta _ 1
displaystyle theta _ 2
are the angles between the normal (to the interface) and the incident
and refracted waves, respectively.
The index of refraction of a medium is related to the speed, v, of
light in that medium by
where c is the speed of light in vacuum.
Snell's Law can be used to predict the deflection of light rays as
they pass through linear media as long as the indexes of refraction
and the geometry of the media are known. For example, the propagation
of light through a prism results in the light ray being deflected
depending on the shape and orientation of the prism. In most
materials, the index of refraction varies with the frequency of the
light. Taking this into account,
Snell's Law can be used to predict
how a prism will disperse light into a spectrum. The discovery of this
phenomenon when passing light through a prism is famously attributed
to Isaac Newton.
Some media have an index of refraction which varies gradually with
position and, thus, light rays in the medium are curved. This effect
is responsible for mirages seen on hot days: a change in index of
refraction air with height causes light rays to bend, creating the
appearance of specular reflections in the distance (as if on the
surface of a pool of water). Optical materials with varying index of
refraction are called gradient-index (GRIN) materials. Such materials
are used to make gradient-index optics.
For light rays travelling from a material with a high index of
refraction to a material with a low index of refraction, Snell's law
predicts that there is no
displaystyle theta _ 2
displaystyle theta _ 1
is large. In this case, no transmission occurs; all the light is
reflected. This phenomenon is called total internal reflection and
allows for fibre optics technology. As light travels down an optical
fibre, it undergoes total internal reflection allowing for essentially
no light to be lost over the length of the cable.
Main article: Lens (optics)
A ray tracing diagram for a converging lens.
A device which produces converging or diverging light rays due to
refraction is known as a lens. Lenses are characterized by their focal
length: a converging lens has positive focal length, while a diverging
lens has negative focal length. Smaller focal length indicates that
the lens has a stronger converging or diverging effect. The focal
length of a simple lens in air is given by the lensmaker's
Ray tracing can be used to show how images are formed by a lens. For a
thin lens in air, the location of the image is given by the simple
displaystyle frac 1 S_ 1 + frac 1 S_ 2 = frac 1 f
displaystyle S_ 1
is the distance from the object to the lens,
displaystyle S_ 2
is the distance from the lens to the image, and
is the focal length of the lens. In the sign convention used here,
the object and image distances are positive if the object and image
are on opposite sides of the lens.
Incoming parallel rays are focused by a converging lens onto a spot
one focal length from the lens, on the far side of the lens. This is
called the rear focal point of the lens. Rays from an object at finite
distance are focused further from the lens than the focal distance;
the closer the object is to the lens, the further the image is from
With diverging lenses, incoming parallel rays diverge after going
through the lens, in such a way that they seem to have originated at a
spot one focal length in front of the lens. This is the lens's front
focal point. Rays from an object at finite distance are associated
with a virtual image that is closer to the lens than the focal point,
and on the same side of the lens as the object. The closer the object
is to the lens, the closer the virtual image is to the lens. As with
mirrors, upright images produced by a single lens are virtual, while
inverted images are real.
Lenses suffer from aberrations that distort images. Monochromatic
aberrations occur because the geometry of the lens does not perfectly
direct rays from each object point to a single point on the image,
while chromatic aberration occurs because the index of refraction of
the lens varies with the wavelength of the light.
Images of black letters in a thin convex lens of focal length f
are shown in red. Selected rays are shown for letters E, I and K in
blue, green and orange, respectively. Note that E (at 2f) has an
equal-size, real and inverted image; I (at f) has its image at
infinity; and K (at f/2) has a double-size, virtual and upright image.
Main article: Physical optics
In physical optics, light is considered to propagate as a wave. This
model predicts phenomena such as interference and diffraction, which
are not explained by geometric optics. The speed of light waves in air
is approximately 3.0×108 m/s (exactly 299,792,458 m/s in
vacuum). The wavelength of visible light waves varies between 400 and
700 nm, but the term "light" is also often applied to infrared
(0.7–300 μm) and ultraviolet radiation (10–400 nm).
The wave model can be used to make predictions about how an optical
system will behave without requiring an explanation of what is
"waving" in what medium. Until the middle of the 19th century, most
physicists believed in an "ethereal" medium in which the light
disturbance propagated. The existence of electromagnetic waves was
predicted in 1865 by Maxwell's equations. These waves propagate at the
speed of light and have varying electric and magnetic fields which are
orthogonal to one another, and also to the direction of propagation of
Light waves are now generally treated as
electromagnetic waves except when quantum mechanical effects have to
Modelling and design of optical systems using physical optics
Many simplified approximations are available for analysing and
designing optical systems. Most of these use a single scalar quantity
to represent the electric field of the light wave, rather than using a
vector model with orthogonal electric and magnetic vectors. The
Huygens–Fresnel equation is one such model. This was derived
empirically by Fresnel in 1815, based on Huygens' hypothesis that each
point on a wavefront generates a secondary spherical wavefront, which
Fresnel combined with the principle of superposition of waves. The
Kirchhoff diffraction equation, which is derived using Maxwell's
equations, puts the Huygens-Fresnel equation on a firmer physical
foundation. Examples of the application of Huygens–Fresnel principle
can be found in the sections on diffraction and Fraunhofer
More rigorous models, involving the modelling of both electric and
magnetic fields of the light wave, are required when dealing with the
detailed interaction of light with materials where the interaction
depends on their electric and magnetic properties. For instance, the
behaviour of a light wave interacting with a metal surface is quite
different from what happens when it interacts with a dielectric
material. A vector model must also be used to model polarised light.
Numerical modeling techniques such as the finite element method, the
boundary element method and the transmission-line matrix method can be
used to model the propagation of light in systems which cannot be
solved analytically. Such models are computationally demanding and are
normally only used to solve small-scale problems that require accuracy
beyond that which can be achieved with analytical solutions.
All of the results from geometrical optics can be recovered using the
Fourier optics which apply many of the same mathematical
and analytical techniques used in acoustic engineering and signal
Gaussian beam propagation is a simple paraxial physical optics model
for the propagation of coherent radiation such as laser beams. This
technique partially accounts for diffraction, allowing accurate
calculations of the rate at which a laser beam expands with distance,
and the minimum size to which the beam can be focused. Gaussian beam
propagation thus bridges the gap between geometric and physical
Superposition and interference
Superposition principle and Interference (optics)
In the absence of nonlinear effects, the superposition principle can
be used to predict the shape of interacting waveforms through the
simple addition of the disturbances. This interaction of waves to
produce a resulting pattern is generally termed "interference" and can
result in a variety of outcomes. If two waves of the same wavelength
and frequency are in phase, both the wave crests and wave troughs
align. This results in constructive interference and an increase in
the amplitude of the wave, which for light is associated with a
brightening of the waveform in that location. Alternatively, if the
two waves of the same wavelength and frequency are out of phase, then
the wave crests will align with wave troughs and vice versa. This
results in destructive interference and a decrease in the amplitude of
the wave, which for light is associated with a dimming of the waveform
at that location. See below for an illustration of this effect.
Two waves in phase
Two waves 180° out
When oil or fuel is spilled, colourful patterns are formed by
Huygens–Fresnel principle states that every point of a
wavefront is associated with the production of a new disturbance, it
is possible for a wavefront to interfere with itself constructively or
destructively at different locations producing bright and dark fringes
in regular and predictable patterns.
Interferometry is the science
of measuring these patterns, usually as a means of making precise
determinations of distances or angular resolutions. The Michelson
interferometer was a famous instrument which used interference effects
to accurately measure the speed of light.
The appearance of thin films and coatings is directly affected by
interference effects. Antireflective coatings use destructive
interference to reduce the reflectivity of the surfaces they coat, and
can be used to minimise glare and unwanted reflections. The simplest
case is a single layer with thickness one-fourth the wavelength of
incident light. The reflected wave from the top of the film and the
reflected wave from the film/material interface are then exactly 180°
out of phase, causing destructive interference. The waves are only
exactly out of phase for one wavelength, which would typically be
chosen to be near the centre of the visible spectrum, around
550 nm. More complex designs using multiple layers can achieve
low reflectivity over a broad band, or extremely low reflectivity at a
Constructive interference in thin films can create strong reflection
of light in a range of wavelengths, which can be narrow or broad
depending on the design of the coating. These films are used to make
dielectric mirrors, interference filters, heat reflectors, and filters
for colour separation in colour television cameras. This interference
effect is also what causes the colourful rainbow patterns seen in oil
Diffraction and optical resolution
Diffraction and Optical resolution
Diffraction on two slits separated by distance
. The bright fringes occur along lines where black lines intersect
with black lines and white lines intersect with white lines. These
fringes are separated by angle
and are numbered as order
Diffraction is the process by which light interference is most
commonly observed. The effect was first described in 1665 by Francesco
Maria Grimaldi, who also coined the term from the Latin diffringere,
'to break into pieces'. Later that century,
Robert Hooke and
Isaac Newton also described phenomena now known to be diffraction in
Newton's rings while James Gregory recorded his observations of
diffraction patterns from bird feathers.
The first physical optics model of diffraction that relied on the
Huygens–Fresnel principle was developed in 1803 by Thomas Young in
his interference experiments with the interference patterns of two
closely spaced slits. Young showed that his results could only be
explained if the two slits acted as two unique sources of waves rather
than corpuscles. In 1815 and 1818,
Augustin-Jean Fresnel firmly
established the mathematics of how wave interference can account for
The simplest physical models of diffraction use equations that
describe the angular separation of light and dark fringes due to light
of a particular wavelength (λ). In general, the equation takes the
displaystyle mlambda =dsin theta
is the separation between two wavefront sources (in the case of
Young's experiments, it was two slits),
is the angular separation between the central fringe and the
th order fringe, where the central maximum is
This equation is modified slightly to take into account a variety of
situations such as diffraction through a single gap, diffraction
through multiple slits, or diffraction through a diffraction grating
that contains a large number of slits at equal spacing. More
complicated models of diffraction require working with the mathematics
of Fresnel or Fraunhofer diffraction.
X-ray diffraction makes use of the fact that atoms in a crystal have
regular spacing at distances that are on the order of one angstrom. To
see diffraction patterns, x-rays with similar wavelengths to that
spacing are passed through the crystal. Since crystals are
three-dimensional objects rather than two-dimensional gratings, the
associated diffraction pattern varies in two directions according to
Bragg reflection, with the associated bright spots occurring in unique
being twice the spacing between atoms.
Diffraction effects limit the ability for an optical detector to
optically resolve separate light sources. In general, light that is
passing through an aperture will experience diffraction and the best
images that can be created (as described in diffraction-limited
optics) appear as a central spot with surrounding bright rings,
separated by dark nulls; this pattern is known as an Airy pattern, and
the central bright lobe as an Airy disk. The size of such a disk
is given by
displaystyle sin theta =1.22 frac lambda D
where θ is the angular resolution, λ is the wavelength of the light,
and D is the diameter of the lens aperture. If the angular separation
of the two points is significantly less than the
Airy disk angular
radius, then the two points cannot be resolved in the image, but if
their angular separation is much greater than this, distinct images of
the two points are formed and they can therefore be resolved. Rayleigh
defined the somewhat arbitrary "Rayleigh criterion" that two points
whose angular separation is equal to the
Airy disk radius (measured to
first null, that is, to the first place where no light is seen) can be
considered to be resolved. It can be seen that the greater the
diameter of the lens or its aperture, the finer the resolution.
Interferometry, with its ability to mimic extremely large baseline
apertures, allows for the greatest angular resolution possible.
For astronomical imaging, the atmosphere prevents optimal resolution
from being achieved in the visible spectrum due to the atmospheric
scattering and dispersion which cause stars to twinkle. Astronomers
refer to this effect as the quality of astronomical seeing. Techniques
known as adaptive optics have been used to eliminate the atmospheric
disruption of images and achieve results that approach the diffraction
Dispersion and scattering
Dispersion (optics) and Scattering
Conceptual animation of light dispersion through a prism. High
frequency (blue) light is deflected the most, and low frequency (red)
Refractive processes take place in the physical optics limit, where
the wavelength of light is similar to other distances, as a kind of
scattering. The simplest type of scattering is Thomson scattering
which occurs when electromagnetic waves are deflected by single
particles. In the limit of Thomson scattering, in which the wavelike
nature of light is evident, light is dispersed independent of the
frequency, in contrast to
Compton scattering which is
frequency-dependent and strictly a quantum mechanical process,
involving the nature of light as particles. In a statistical sense,
elastic scattering of light by numerous particles much smaller than
the wavelength of the light is a process known as Rayleigh scattering
while the similar process for scattering by particles that are similar
or larger in wavelength is known as
Mie scattering with the Tyndall
effect being a commonly observed result. A small proportion of light
scattering from atoms or molecules may undergo Raman scattering,
wherein the frequency changes due to excitation of the atoms and
Brillouin scattering occurs when the frequency of light
changes due to local changes with time and movements of a dense
Dispersion occurs when different frequencies of light have different
phase velocities, due either to material properties (material
dispersion) or to the geometry of an optical waveguide (waveguide
dispersion). The most familiar form of dispersion is a decrease in
index of refraction with increasing wavelength, which is seen in most
transparent materials. This is called "normal dispersion". It occurs
in all dielectric materials, in wavelength ranges where the material
does not absorb light. In wavelength ranges where a medium has
significant absorption, the index of refraction can increase with
wavelength. This is called "anomalous dispersion".
The separation of colours by a prism is an example of normal
dispersion. At the surfaces of the prism,
Snell's law predicts that
light incident at an angle θ to the normal will be refracted at an
angle arcsin(sin (θ) / n). Thus, blue light, with its higher
refractive index, is bent more strongly than red light, resulting in
the well-known rainbow pattern.
Dispersion: two sinusoids propagating at different speeds make a
moving interference pattern. The red dot moves with the phase
velocity, and the green dots propagate with the group velocity. In
this case, the phase velocity is twice the group velocity. The red dot
overtakes two green dots, when moving from the left to the right of
the figure. In effect, the individual waves (which travel with the
phase velocity) escape from the wave packet (which travels with the
Material dispersion is often characterised by the Abbe number, which
gives a simple measure of dispersion based on the index of refraction
at three specific wavelengths. Waveguide dispersion is dependent on
the propagation constant. Both kinds of dispersion cause changes
in the group characteristics of the wave, the features of the wave
packet that change with the same frequency as the amplitude of the
electromagnetic wave. "
Group velocity dispersion" manifests as a
spreading-out of the signal "envelope" of the radiation and can be
quantified with a group dispersion delay parameter:
displaystyle D= frac 1 v_ g ^ 2 frac dv_ g dlambda
displaystyle v_ g
is the group velocity. For a uniform medium, the group velocity
displaystyle v_ g =cleft(n-lambda frac dn dlambda right)^ -1
where n is the index of refraction and c is the speed of light in a
vacuum. This gives a simpler form for the dispersion delay
displaystyle D=- frac lambda c , frac d^ 2 n dlambda ^ 2
If D is less than zero, the medium is said to have positive dispersion
or normal dispersion. If D is greater than zero, the medium has
negative dispersion. If a light pulse is propagated through a normally
dispersive medium, the result is the higher frequency components slow
down more than the lower frequency components. The pulse therefore
becomes positively chirped, or up-chirped, increasing in frequency
with time. This causes the spectrum coming out of a prism to appear
with red light the least refracted and blue/violet light the most
refracted. Conversely, if a pulse travels through an anomalously
(negatively) dispersive medium, high frequency components travel
faster than the lower ones, and the pulse becomes negatively chirped,
or down-chirped, decreasing in frequency with time.
The result of group velocity dispersion, whether negative or positive,
is ultimately temporal spreading of the pulse. This makes dispersion
management extremely important in optical communications systems based
on optical fibres, since if dispersion is too high, a group of pulses
representing information will each spread in time and merge, making it
impossible to extract the signal.
Main article: Polarization (waves)
Polarization is a general property of waves that describes the
orientation of their oscillations. For transverse waves such as many
electromagnetic waves, it describes the orientation of the
oscillations in the plane perpendicular to the wave's direction of
travel. The oscillations may be oriented in a single direction (linear
polarization), or the oscillation direction may rotate as the wave
travels (circular or elliptical polarization). Circularly polarised
waves can rotate rightward or leftward in the direction of travel, and
which of those two rotations is present in a wave is called the wave's
The typical way to consider polarization is to keep track of the
orientation of the electric field vector as the electromagnetic wave
propagates. The electric field vector of a plane wave may be
arbitrarily divided into two perpendicular components labeled x and y
(with z indicating the direction of travel). The shape traced out in
the x-y plane by the electric field vector is a Lissajous figure that
describes the polarization state. The following figures show some
examples of the evolution of the electric field vector (blue), with
time (the vertical axes), at a particular point in space, along with
its x and y components (red/left and green/right), and the path traced
by the vector in the plane (purple): The same evolution would occur
when looking at the electric field at a particular time while evolving
the point in space, along the direction opposite to propagation.
In the leftmost figure above, the x and y components of the light wave
are in phase. In this case, the ratio of their strengths is constant,
so the direction of the electric vector (the vector sum of these two
components) is constant. Since the tip of the vector traces out a
single line in the plane, this special case is called linear
polarization. The direction of this line depends on the relative
amplitudes of the two components.
In the middle figure, the two orthogonal components have the same
amplitudes and are 90° out of phase. In this case, one component is
zero when the other component is at maximum or minimum amplitude.
There are two possible phase relationships that satisfy this
requirement: the x component can be 90° ahead of the y component or
it can be 90° behind the y component. In this special case, the
electric vector traces out a circle in the plane, so this polarization
is called circular polarization. The rotation direction in the circle
depends on which of the two phase relationships exists and corresponds
to right-hand circular polarization and left-hand circular
In all other cases, where the two components either do not have the
same amplitudes and/or their phase difference is neither zero nor a
multiple of 90°, the polarization is called elliptical polarization
because the electric vector traces out an ellipse in the plane (the
polarization ellipse). This is shown in the above figure on the right.
Detailed mathematics of polarization is done using
Jones calculus and
is characterised by the Stokes parameters.
Media that have different indexes of refraction for different
polarization modes are called birefringent. Well known
manifestations of this effect appear in optical wave plates/retarders
(linear modes) and in Faraday rotation/optical rotation (circular
modes). If the path length in the birefringent medium is
sufficient, plane waves will exit the material with a significantly
different propagation direction, due to refraction. For example, this
is the case with macroscopic crystals of calcite, which present the
viewer with two offset, orthogonally polarised images of whatever is
viewed through them. It was this effect that provided the first
discovery of polarization, by
Erasmus Bartholinus in 1669. In
addition, the phase shift, and thus the change in polarization state,
is usually frequency dependent, which, in combination with dichroism,
often gives rise to bright colours and rainbow-like effects. In
mineralogy, such properties, known as pleochroism, are frequently
exploited for the purpose of identifying minerals using polarization
microscopes. Additionally, many plastics that are not normally
birefringent will become so when subject to mechanical stress, a
phenomenon which is the basis of photoelasticity. Non-birefringent
methods, to rotate the linear polarization of light beams, include the
use of prismatic polarization rotators which use total internal
reflection in a prism set designed for efficient collinear
A polariser changing the orientation of linearly polarised light.
In this picture, θ1 – θ0 = θi.
Media that reduce the amplitude of certain polarization modes are
called dichroic, with devices that block nearly all of the radiation
in one mode known as polarizing filters or simply "polarisers". Malus'
law, which is named after Étienne-Louis Malus, says that when a
perfect polariser is placed in a linear polarised beam of light, the
intensity, I, of the light that passes through is given by
displaystyle I=I_ 0 cos ^ 2 theta _ i quad ,
I0 is the initial intensity,
and θi is the angle between the light's initial polarization
direction and the axis of the polariser.
A beam of unpolarised light can be thought of as containing a uniform
mixture of linear polarizations at all possible angles. Since the
average value of
displaystyle cos ^ 2 theta
is 1/2, the transmission coefficient becomes
displaystyle frac I I_ 0 = frac 1 2 quad
In practice, some light is lost in the polariser and the actual
transmission of unpolarised light will be somewhat lower than this,
around 38% for Polaroid-type polarisers but considerably higher
(>49.9%) for some birefringent prism types.
In addition to birefringence and dichroism in extended media,
polarization effects can also occur at the (reflective) interface
between two materials of different refractive index. These effects are
treated by the Fresnel equations. Part of the wave is transmitted and
part is reflected, with the ratio depending on angle of incidence and
the angle of refraction. In this way, physical optics recovers
Brewster's angle. When light reflects from a thin film on a
surface, interference between the reflections from the film's surfaces
can produce polarization in the reflected and transmitted light.
The effects of a polarising filter on the sky in a photograph. Left
picture is taken without polariser. For the right picture, filter was
adjusted to eliminate certain polarizations of the scattered blue
light from the sky.
Most sources of electromagnetic radiation contain a large number of
atoms or molecules that emit light. The orientation of the electric
fields produced by these emitters may not be correlated, in which case
the light is said to be unpolarised. If there is partial correlation
between the emitters, the light is partially polarised. If the
polarization is consistent across the spectrum of the source,
partially polarised light can be described as a superposition of a
completely unpolarised component, and a completely polarised one. One
may then describe the light in terms of the degree of polarization,
and the parameters of the polarization ellipse.
Light reflected by shiny transparent materials is partly or fully
polarised, except when the light is normal (perpendicular) to the
surface. It was this effect that allowed the mathematician
Étienne-Louis Malus to make the measurements that allowed for his
development of the first mathematical models for polarised light.
Polarization occurs when light is scattered in the atmosphere. The
scattered light produces the brightness and colour in clear skies.
This partial polarization of scattered light can be taken advantage of
using polarizing filters to darken the sky in photographs. Optical
polarization is principally of importance in chemistry due to circular
dichroism and optical rotation ("circular birefringence") exhibited by
optically active (chiral) molecules.
Optical physics and Optical engineering
Modern optics encompasses the areas of optical science and engineering
that became popular in the 20th century. These areas of optical
science typically relate to the electromagnetic or quantum properties
of light but do include other topics. A major subfield of modern
optics, quantum optics, deals with specifically quantum mechanical
properties of light.
Quantum optics is not just theoretical; some
modern devices, such as lasers, have principles of operation that
depend on quantum mechanics.
Light detectors, such as photomultipliers
and channeltrons, respond to individual photons. Electronic image
sensors, such as CCDs, exhibit shot noise corresponding to the
statistics of individual photon events. Light-emitting diodes and
photovoltaic cells, too, cannot be understood without quantum
mechanics. In the study of these devices, quantum optics often
overlaps with quantum electronics.
Specialty areas of optics research include the study of how light
interacts with specific materials as in crystal optics and
metamaterials. Other research focuses on the phenomenology of
electromagnetic waves as in singular optics, non-imaging optics,
non-linear optics, statistical optics, and radiometry. Additionally,
computer engineers have taken an interest in integrated optics,
machine vision, and photonic computing as possible components of the
"next generation" of computers.
Today, the pure science of optics is called optical science or optical
physics to distinguish it from applied optical sciences, which are
referred to as optical engineering. Prominent subfields of optical
engineering include illumination engineering, photonics, and
optoelectronics with practical applications like lens design,
fabrication and testing of optical components, and image processing.
Some of these fields overlap, with nebulous boundaries between the
subjects terms that mean slightly different things in different parts
of the world and in different areas of industry. A professional
community of researchers in nonlinear optics has developed in the last
several decades due to advances in laser technology.
Main article: Laser
Experiments such as this one with high-power lasers are part of the
modern optics research.
A laser is a device that emits light (electromagnetic radiation)
through a process called stimulated emission. The term laser is an
Light Amplification by Stimulated Emission of
Laser light is usually spatially coherent, which means
that the light either is emitted in a narrow, low-divergence beam, or
can be converted into one with the help of optical components such as
lenses. Because the microwave equivalent of the laser, the maser, was
developed first, devices that emit microwave and radio frequencies are
usually called masers.
VLT’s laser guided star.
The first working laser was demonstrated on 16 May 1960 by Theodore
Maiman at Hughes Research Laboratories. When first invented, they
were called "a solution looking for a problem". Since then, lasers
have become a multibillion-dollar industry, finding utility in
thousands of highly varied applications. The first application of
lasers visible in the daily lives of the general population was the
supermarket barcode scanner, introduced in 1974. The laserdisc
player, introduced in 1978, was the first successful consumer product
to include a laser, but the compact disc player was the first
laser-equipped device to become truly common in consumers' homes,
beginning in 1982. These optical storage devices use a
semiconductor laser less than a millimetre wide to scan the surface of
the disc for data retrieval.
Fibre-optic communication relies on
lasers to transmit large amounts of information at the speed of light.
Other common applications of lasers include laser printers and laser
pointers. Lasers are used in medicine in areas such as bloodless
surgery, laser eye surgery, and laser capture microdissection and in
military applications such as missile defence systems, electro-optical
countermeasures (EOCM), and lidar. Lasers are also used in holograms,
bubblegrams, laser light shows, and laser hair removal.
Kapitsa–Dirac effect causes beams of particles to diffract as
the result of meeting a standing wave of light.
Light can be used to
position matter using various phenomena (see optical tweezers).
Optics is part of everyday life. The ubiquity of visual systems in
biology indicates the central role optics plays as the science of one
of the five senses. Many people benefit from eyeglasses or contact
lenses, and optics are integral to the functioning of many consumer
goods including cameras. Rainbows and mirages are examples of optical
Optical communication provides the backbone for both the
Internet and modern telephony.
Model of a human eye. Features mentioned in this article are 3.
ciliary muscle, 6. pupil, 8. cornea, 10. lens cortex, 22. optic nerve,
26. fovea, 30. retina
Human eye and Photometry (optics)
The human eye functions by focusing light onto a layer of
photoreceptor cells called the retina, which forms the inner lining of
the back of the eye. The focusing is accomplished by a series of
Light entering the eye passes first through the
cornea, which provides much of the eye's optical power. The light then
continues through the fluid just behind the cornea—the anterior
chamber, then passes through the pupil. The light then passes through
the lens, which focuses the light further and allows adjustment of
focus. The light then passes through the main body of fluid in the
eye—the vitreous humour, and reaches the retina. The cells in the
retina line the back of the eye, except for where the optic nerve
exits; this results in a blind spot.
There are two types of photoreceptor cells, rods and cones, which are
sensitive to different aspects of light. Rod cells are sensitive
to the intensity of light over a wide frequency range, thus are
responsible for black-and-white vision. Rod cells are not present on
the fovea, the area of the retina responsible for central vision, and
are not as responsive as cone cells to spatial and temporal changes in
light. There are, however, twenty times more rod cells than cone cells
in the retina because the rod cells are present across a wider area.
Because of their wider distribution, rods are responsible for
In contrast, cone cells are less sensitive to the overall intensity of
light, but come in three varieties that are sensitive to different
frequency-ranges and thus are used in the perception of colour and
photopic vision. Cone cells are highly concentrated in the fovea and
have a high visual acuity meaning that they are better at spatial
resolution than rod cells. Since cone cells are not as sensitive to
dim light as rod cells, most night vision is limited to rod cells.
Likewise, since cone cells are in the fovea, central vision (including
the vision needed to do most reading, fine detail work such as sewing,
or careful examination of objects) is done by cone cells.
Ciliary muscles around the lens allow the eye's focus to be adjusted.
This process is known as accommodation. The near point and far point
define the nearest and farthest distances from the eye at which an
object can be brought into sharp focus. For a person with normal
vision, the far point is located at infinity. The near point's
location depends on how much the muscles can increase the curvature of
the lens, and how inflexible the lens has become with age.
Optometrists, ophthalmologists, and opticians usually consider an
appropriate near point to be closer than normal reading
distance—approximately 25 cm.
Defects in vision can be explained using optical principles. As people
age, the lens becomes less flexible and the near point recedes from
the eye, a condition known as presbyopia. Similarly, people suffering
from hyperopia cannot decrease the focal length of their lens enough
to allow for nearby objects to be imaged on their retina. Conversely,
people who cannot increase the focal length of their lens enough to
allow for distant objects to be imaged on the retina suffer from
myopia and have a far point that is considerably closer than infinity.
A condition known as astigmatism results when the cornea is not
spherical but instead is more curved in one direction. This causes
horizontally extended objects to be focused on different parts of the
retina than vertically extended objects, and results in distorted
All of these conditions can be corrected using corrective lenses. For
presbyopia and hyperopia, a converging lens provides the extra
curvature necessary to bring the near point closer to the eye while
for myopia a diverging lens provides the curvature necessary to send
the far point to infinity. Astigmatism is corrected with a cylindrical
surface lens that curves more strongly in one direction than in
another, compensating for the non-uniformity of the cornea.
The optical power of corrective lenses is measured in diopters, a
value equal to the reciprocal of the focal length measured in metres;
with a positive focal length corresponding to a converging lens and a
negative focal length corresponding to a diverging lens. For lenses
that correct for astigmatism as well, three numbers are given: one for
the spherical power, one for the cylindrical power, and one for the
angle of orientation of the astigmatism.
Optical illusions and Perspective (graphical)
For the visual effects used in film, video, and computer graphics, see
The Ponzo Illusion relies on the fact that parallel lines appear to
converge as they approach infinity.
Optical illusions (also called visual illusions) are characterized by
visually perceived images that differ from objective reality. The
information gathered by the eye is processed in the brain to give a
percept that differs from the object being imaged. Optical illusions
can be the result of a variety of phenomena including physical effects
that create images that are different from the objects that make them,
the physiological effects on the eyes and brain of excessive
stimulation (e.g. brightness, tilt, colour, movement), and cognitive
illusions where the eye and brain make unconscious inferences.
Cognitive illusions include some which result from the unconscious
misapplication of certain optical principles. For example, the Ames
room, Hering, Müller-Lyer, Orbison, Ponzo, Sander, and Wundt
illusions all rely on the suggestion of the appearance of distance by
using converging and diverging lines, in the same way that parallel
light rays (or indeed any set of parallel lines) appear to converge at
a vanishing point at infinity in two-dimensionally rendered images
with artistic perspective. This suggestion is also responsible for
the famous moon illusion where the moon, despite having essentially
the same angular size, appears much larger near the horizon than it
does at zenith. This illusion so confounded
Ptolemy that he
incorrectly attributed it to atmospheric refraction when he described
it in his treatise, Optics.
Another type of optical illusion exploits broken patterns to trick the
mind into perceiving symmetries or asymmetries that are not present.
Examples include the café wall, Ehrenstein, Fraser spiral,
Poggendorff, and Zöllner illusions. Related, but not strictly
illusions, are patterns that occur due to the superimposition of
periodic structures. For example, transparent tissues with a grid
structure produce shapes known as moiré patterns, while the
superimposition of periodic transparent patterns comprising parallel
opaque lines or curves produces line moiré patterns.
Illustrations of various optical instruments from the 1728 Cyclopaedia
Main article: Optical instruments
Single lenses have a variety of applications including photographic
lenses, corrective lenses, and magnifying glasses while single mirrors
are used in parabolic reflectors and rear-view mirrors. Combining a
number of mirrors, prisms, and lenses produces compound optical
instruments which have practical uses. For example, a periscope is
simply two plane mirrors aligned to allow for viewing around
obstructions. The most famous compound optical instruments in science
are the microscope and the telescope which were both invented by the
Dutch in the late 16th century.
Microscopes were first developed with just two lenses: an objective
lens and an eyepiece. The objective lens is essentially a magnifying
glass and was designed with a very small focal length while the
eyepiece generally has a longer focal length. This has the effect of
producing magnified images of close objects. Generally, an additional
source of illumination is used since magnified images are dimmer due
to the conservation of energy and the spreading of light rays over a
larger surface area. Modern microscopes, known as compound microscopes
have many lenses in them (typically four) to optimize the
functionality and enhance image stability. A slightly different
variety of microscope, the comparison microscope, looks at
side-by-side images to produce a stereoscopic binocular view that
appears three dimensional when used by humans.
The first telescopes, called refracting telescopes were also developed
with a single objective and eyepiece lens. In contrast to the
microscope, the objective lens of the telescope was designed with a
large focal length to avoid optical aberrations. The objective focuses
an image of a distant object at its focal point which is adjusted to
be at the focal point of an eyepiece of a much smaller focal length.
The main goal of a telescope is not necessarily magnification, but
rather collection of light which is determined by the physical size of
the objective lens. Thus, telescopes are normally indicated by the
diameters of their objectives rather than by the magnification which
can be changed by switching eyepieces. Because the magnification of a
telescope is equal to the focal length of the objective divided by the
focal length of the eyepiece, smaller focal-length eyepieces cause
Since crafting large lenses is much more difficult than crafting large
mirrors, most modern telescopes are reflecting telescopes, that is,
telescopes that use a primary mirror rather than an objective lens.
The same general optical considerations apply to reflecting telescopes
that applied to refracting telescopes, namely, the larger the primary
mirror, the more light collected, and the magnification is still equal
to the focal length of the primary mirror divided by the focal length
of the eyepiece. Professional telescopes generally do not have
eyepieces and instead place an instrument (often a charge-coupled
device) at the focal point instead.
Main article: Science of photography
Photograph taken with aperture f/32
Photograph taken with aperture f/5
The optics of photography involves both lenses and the medium in which
the electromagnetic radiation is recorded, whether it be a plate,
film, or charge-coupled device. Photographers must consider the
reciprocity of the camera and the shot which is summarized by the
Exposure ∝ ApertureArea × ExposureTime × SceneLuminance
In other words, the smaller the aperture (giving greater depth of
focus), the less light coming in, so the length of time has to be
increased (leading to possible blurriness if motion occurs). An
example of the use of the law of reciprocity is the Sunny 16 rule
which gives a rough estimate for the settings needed to estimate the
proper exposure in daylight.
A camera's aperture is measured by a unitless number called the
f-number or f-stop, f/#, often notated as
, and given by
displaystyle f/#=N= frac f D
is the focal length, and
is the diameter of the entrance pupil. By convention, "f/#" is
treated as a single symbol, and specific values of f/# are written by
replacing the number sign with the value. The two ways to increase the
f-stop are to either decrease the diameter of the entrance pupil or
change to a longer focal length (in the case of a zoom lens, this can
be done by simply adjusting the lens). Higher f-numbers also have a
larger depth of field due to the lens approaching the limit of a
pinhole camera which is able to focus all images perfectly, regardless
of distance, but requires very long exposure times.
The field of view that the lens will provide changes with the focal
length of the lens. There are three basic classifications based on the
relationship to the diagonal size of the film or sensor size of the
camera to the focal length of the lens:
Normal lens: angle of view of about 50° (called normal because this
angle considered roughly equivalent to human vision) and a focal
length approximately equal to the diagonal of the film or sensor.
Wide-angle lens: angle of view wider than 60° and focal length
shorter than a normal lens.
Long focus lens: angle of view narrower than a normal lens. This is
any lens with a focal length longer than the diagonal measure of the
film or sensor. The most common type of long focus lens is the
telephoto lens, a design that uses a special telephoto group to be
physically shorter than its focal length.
Modern zoom lenses may have some or all of these attributes.
The absolute value for the exposure time required depends on how
sensitive to light the medium being used is (measured by the film
speed, or, for digital media, by the quantum efficiency). Early
photography used media that had very low light sensitivity, and so
exposure times had to be long even for very bright shots. As
technology has improved, so has the sensitivity through film cameras
and digital cameras.
Other results from physical and geometrical optics apply to camera
optics. For example, the maximum resolution capability of a particular
camera set-up is determined by the diffraction limit associated with
the pupil size and given, roughly, by the Rayleigh criterion.
Main article: Atmospheric optics
A colourful sky is often due to scattering of light off particulates
and pollution, as in this photograph of a sunset during the October
2007 California wildfires.
The unique optical properties of the atmosphere cause a wide range of
spectacular optical phenomena. The blue colour of the sky is a direct
Rayleigh scattering which redirects higher frequency (blue)
sunlight back into the field of view of the observer. Because blue
light is scattered more easily than red light, the sun takes on a
reddish hue when it is observed through a thick atmosphere, as during
a sunrise or sunset. Additional particulate matter in the sky can
scatter different colours at different angles creating colourful
glowing skies at dusk and dawn.
Scattering off of ice crystals and
other particles in the atmosphere are responsible for halos,
afterglows, coronas, rays of sunlight, and sun dogs. The variation in
these kinds of phenomena is due to different particle sizes and
Mirages are optical phenomena in which light rays are bent due to
thermal variations in the refraction index of air, producing displaced
or heavily distorted images of distant objects. Other dramatic optical
phenomena associated with this include the
Novaya Zemlya effect
Novaya Zemlya effect where
the sun appears to rise earlier than predicted with a distorted shape.
A spectacular form of refraction occurs with a temperature inversion
called the Fata Morgana where objects on the horizon or even beyond
the horizon, such as islands, cliffs, ships or icebergs, appear
elongated and elevated, like "fairy tale castles".
Rainbows are the result of a combination of internal reflection and
dispersive refraction of light in raindrops. A single reflection off
the backs of an array of raindrops produces a rainbow with an angular
size on the sky that ranges from 40° to 42° with red on the outside.
Double rainbows are produced by two internal reflections with angular
size of 50.5° to 54° with violet on the outside. Because rainbows
are seen with the sun 180° away from the centre of the rainbow,
rainbows are more prominent the closer the sun is to the horizon.
Important publications in optics
List of optical topics
^ a b McGraw-Hill Encyclopedia of Science and Technology (5th ed.).
^ "World's oldest telescope?".
BBC News. July 1, 1999. Archived from
the original on February 1, 2009. Retrieved Jan 3, 2010.
^ T. F. Hoad (1996). The Concise Oxford Dictionary of English
Etymology. ISBN 0-19-283098-8.
^ A History Of The Eye Archived 2012-01-20 at the Wayback Machine..
stanford.edu. Retrieved 2012-06-10.
^ T. L. Heath (2003). A manual of greek mathematics. Courier Dover
Publications. pp. 181–182. ISBN 0-486-43231-9.
^ William R. Uttal (1983). Visual Form Detection in 3-Dimensional
Space. Psychology Press. pp. 25–. ISBN 978-0-89859-289-4.
Archived from the original on 2016-05-03.
Euclid (1999). Elaheh Kheirandish, ed. The Arabic version of
Euclid's optics = Kitāb Uqlīdis fī ikhtilāf al-manāẓir. New
York: Springer. ISBN 0-387-98523-9.
^ a b
Ptolemy (1996). A. Mark Smith, ed. Ptolemy's theory of visual
perception: an English translation of the
Optics with introduction and
commentary. DIANE Publishing. ISBN 0-87169-862-5.
^ Verma, RL (1969), Al-Hazen: father of modern optics
^ Adamson, Peter (2006). "Al-Kindi¯ and the reception of Greek
philosophy". In Adamson, Peter; Taylor, R.. The Cambridge companion to
Arabic philosophy. Cambridge University Press. p. 45.
^ a b Rashed, Roshdi (1990). "A pioneer in anaclastics: Ibn Sahl on
burning mirrors and lenses". Isis. 81 (3): 464–491.
doi:10.1086/355456. JSTOR 233423.
^ Hogendijk, Jan P.; Sabra, Abdelhamid I., eds. (2003). The Enterprise
of Science in Islam: New Perspectives. MIT Press. pp. 85–118.
ISBN 0-262-19482-1. OCLC 50252039.
^ G. Hatfield (1996). "Was the Scientific Revolution Really a
Revolution in Science?". In F. J. Ragep; P. Sally; S. J. Livesey.
Tradition, Transmission, Transformation: Proceedings of Two
Conferences on Pre-modern Science held at the University of Oklahoma.
Brill Publishers. p. 500. ISBN 90-04-10119-5. Archived from
the original on 2016-04-27.
Nader El-Bizri (2005). "A Philosophical Perspective on Alhazen's
Optics". Arabic Sciences and Philosophy. 15 (2): 189–218.
Nader El-Bizri (2007). "In Defence of the Sovereignty of Philosophy:
al-Baghdadi's Critique of Ibn al-Haytham's Geometrisation of Place".
Arabic Sciences and Philosophy. 17: 57–80.
^ G. Simon (2006). "The Gaze in Ibn al-Haytham". The Medieval History
Journal. 9: 89. doi:10.1177/097194580500900105.
^ Ian P. Howard; Brian J. Rogers (1995). Binocular Vision and
Stereopsis. Oxford University Press. p. 7.
ISBN 978-0-19-508476-4. Archived from the original on
^ Elena Agazzi; Enrico Giannetto; Franco Giudice (2010). Representing
Light Across Arts and Sciences: Theories and Practices. V&R
unipress GmbH. p. 42. ISBN 978-3-89971-735-8. Archived from
the original on 2016-05-10.
^ El-Bizri, Nader (2010). "Classical
Optics and the Perspectiva
Traditions Leading to the Renaissance". In Hendrix, John Shannon;
Carman, Charles H. Renaissance Theories of Vision (Visual Culture in
Early Modernity). Farnham, Surrey: Ashgate. pp. 11–30.
ISBN 1-409400-24-7. ; El-Bizri, Nader (2014). "Seeing
Reality in Perspective: 'The Art of Optics' and the 'Science of
Painting'". In Lupacchini, Rossella; Angelini, Annarita. The Art of
Science: From Perspective Drawing to Quantum Randomness. Doredrecht:
Springer. pp. 25–47.
^ D. C. Lindberg, Theories of Vision from al-Kindi to Kepler,
(Chicago: Univ. of Chicago Pr., 1976), pp. 94–99.
^ Vincent, Ilardi (2007). Renaissance Vision from Spectacles to
Telescopes. Philadelphia, PA: American Philosophical Society.
pp. 4–5. ISBN 978-0-87169-259-7.
^ '''The Galileo Project > Science > The Telescope''' by Al Van
Helden '' Archived 2012-03-20 at the Wayback Machine..
Galileo.rice.edu. Retrieved 2012-06-10.
^ Henry C. King (2003). The History of the Telescope. Courier Dover
Publications. p. 27. ISBN 978-0-486-43265-6. Archived from
the original on 2016-06-17.
^ Paul S. Agutter; Denys N. Wheatley (2008). Thinking about Life: The
History and Philosophy of Biology and Other Sciences. Springer.
p. 17. ISBN 978-1-4020-8865-0. Archived from the original on
^ Ilardi, Vincent (2007). Renaissance Vision from Spectacles to
Telescopes. American Philosophical Society. p. 210.
ISBN 978-0-87169-259-7. Archived from the original on
^ Microscopes: Time Line Archived 2010-01-09 at the Wayback Machine.,
Nobel Foundation. Retrieved April 3, 2009
^ Watson, Fred (2007). Stargazer: The Life and Times of the Telescope.
Allen & Unwin. p. 55. ISBN 978-1-74175-383-7. Archived
from the original on 2016-05-08.
^ Ilardi, Vincent (2007). Renaissance Vision from Spectacles to
Telescopes. American Philosophical Society. p. 244.
ISBN 978-0-87169-259-7. Archived from the original on
^ Caspar, Kepler, pp. 198–202 Archived 2016-05-07 at the Wayback
Machine., Courier Dover Publications, 1993, ISBN 0-486-67605-6.
^ a b A. I. Sabra (1981). Theories of light, from Descartes to Newton.
CUP Archive. ISBN 0-521-28436-8.
^ W. F. Magie (1935). A Source Book in Physics. Harvard University
Press. p. 309.
^ J. C. Maxwell (1865). "A Dynamical Theory of the Electromagnetic
Field". Philosophical Transactions of the Royal Society of London.
155: 459. Bibcode:1865RSPT..155..459C.
^ For a solid approach to the complexity of Planck's intellectual
motivations for the quantum, for his reluctant acceptance of its
implications, see H. Kragh, Max Planck: the reluctant revolutionary,
Physics World. December 2000.
^ Einstein, A. (1967). "On a heuristic viewpoint concerning the
production and transformation of light". In Ter Haar, D. The Old
Quantum Theory (PDF). Pergamon. pp. 91–107. Retrieved March 18,
2010. [permanent dead link] The chapter is an English translation
of Einstein's 1905 paper on the photoelectric effect.
^ Einstein, A. (1905). "Über einen die Erzeugung und Verwandlung des
Lichtes betreffenden heuristischen Gesichtspunkt" [On a heuristic
viewpoint concerning the production and transformation of light].
Annalen der Physik (in German). 322 (6): 132–148.
^ "On the Constitution of Atoms and Molecules". Philosophical
Magazine. 26, Series 6: 1–25. 1913. Archived from the original on
July 4, 2007. . The landmark paper laying the Bohr model of the
atom and molecular bonding.
^ R. Feynman (1985). "Chapter 1". QED: The Strange Theory of
Matter. Princeton University Press. p. 6.
^ N. Taylor (2000). LASER: The inventor, the Nobel laureate, and the
thirty-year patent war. New York: Simon & Schuster.
^ Ariel Lipson; Stephen G. Lipson; Henry Lipson (28 October 2010).
Optical Physics. Cambridge University Press. p. 48.
ISBN 978-0-521-49345-1. Archived from the original on 28 May
2013. Retrieved 12 July 2012.
^ Arthur Schuster (1904). An Introduction to the Theory of Optics. E.
Arnold. p. 41. Archived from the original on 2016-05-13.
^ J. E. Greivenkamp (2004). Field Guide to Geometrical Optics. SPIE
Field Guides vol. FG01. SPIE. pp. 19–20.
^ a b c d e f g h i j H. D. Young (1992). "35". University
Addison-Wesley. ISBN 0-201-52981-5.
^ Marchand, E. W. (1978). Gradient Index Optics. New York: Academic
^ a b c d e f g h i j k l m E. Hecht (1987).
Optics (2nd ed.). Addison
Wesley. ISBN 0-201-11609-X. Chapters 5 & 6.
^ MV Klein & TE Furtak, 1986, Optics, John Wiley & Sons, New
York ISBN 0-471-87297-0.
^ Maxwell, James Clerk (1865). "A dynamical theory of the
electromagnetic field" (PDF). Philosophical Transactions of the Royal
Society of London. 155: 499. doi:10.1098/rstl.1865.0008. Archived
(PDF) from the original on 2011-07-28. This article accompanied
a December 8, 1864 presentation by Maxwell to the Royal Society. See
also A dynamical theory of the electromagnetic field.
^ M. Born and E. Wolf (1999). Principle of Optics. Cambridge:
Cambridge University Press. ISBN 0-521-64222-1.
^ J. Goodman (2005). Introduction to Fourier
Optics (3rd ed, ed.).
Roberts & Co Publishers. ISBN 0-9747077-2-4.
^ A. E. Siegman (1986). Lasers. University Science Books.
ISBN 0-935702-11-3. Chapter 16.
^ a b c d H. D. Young (1992). University
Physics 8e. Addison-Wesley.
ISBN 0-201-52981-5. Chapter 37
^ a b P. Hariharan (2003). Optical
Interferometry (PDF) (2nd ed.). San
Diego, USA: Academic Press. ISBN 0-12-325220-2. Archived (PDF)
from the original on 2008-04-06.
^ E. R. Hoover (1977). Cradle of Greatness: National and World
Achievements of Ohio's Western Reserve. Cleveland: Shaker Savings
^ J. L. Aubert (1760). Memoires pour l'histoire des sciences et des
beaux arts. Paris: Impr. de S. A. S.; Chez E. Ganeau.
^ D. Brewster (1831). A Treatise on Optics. London: Longman, Rees,
Orme, Brown & Green and John Taylor. p. 95.
^ R. Hooke (1665). Micrographia: or, Some physiological descriptions
of minute bodies made by magnifying glasses. London: J. Martyn and J.
Allestry. ISBN 0-486-49564-7.
^ H. W. Turnbull (1940–1941). "Early Scottish Relations with the
Royal Society: I. James Gregory, F.R.S. (1638–1675)". Notes and
Records of the Royal Society of London. 3: 22.
doi:10.1098/rsnr.1940.0003. JSTOR 531136.
^ T. Rothman (2003). Everything's Relative and Other Fables in Science
and Technology. New Jersey: Wiley. ISBN 0-471-20257-6.
^ a b c d H. D. Young (1992). University
Physics 8e. Addison-Wesley.
ISBN 0-201-52981-5. Chapter 38
^ R. S. Longhurst (1968). Geometrical and Physical Optics, 2nd
Edition. London: Longmans.
^ Lucky Exposures:
Diffraction limited astronomical imaging through
the atmosphere Archived 2008-10-05 at the Wayback Machine. by Robert
^ C. F. Bohren & D. R. Huffman (1983). Absorption and Scattering
Light by Small Particles. Wiley. ISBN 0-471-29340-7.
^ a b J. D. Jackson (1975). Classical Electrodynamics (2nd ed.).
Wiley. p. 286. ISBN 0-471-43132-X.
^ a b R. Ramaswami; K. N. Sivarajan (1998). Optical Networks: A
Practical Perspective. London: Academic Press.
ISBN 0-12-374092-4. Archived from the original on
^ Brillouin, Léon.
Wave Propagation and Group Velocity. Academic
Press Inc., New York (1960)
^ M. Born & E. Wolf (1999). Principle of Optics. Cambridge:
Cambridge University Press. pp. 14–24.
^ a b c d e f H. D. Young (1992). University
Addison-Wesley. ISBN 0-201-52981-5. Chapter 34
F. J. Duarte
F. J. Duarte (2015). Tunable
Optics (2nd ed.). New York: CRC.
pp. 117–120. ISBN 978-1-4822-4529-5. Archived from the
original on 2015-04-02.
^ D. F. Walls and G. J. Milburn Quantum
Optics (Springer 1994)
^ Alastair D. McAulay (16 January 1991). Optical computer
architectures: the application of optical concepts to next generation
computers. Wiley. ISBN 978-0-471-63242-9. Archived from the
original on 29 May 2013. Retrieved 12 July 2012.
^ Y. R. Shen (1984). The principles of nonlinear optics. New York,
Wiley-Interscience. ISBN 0-471-88998-9.
^ "laser". Reference.com. Archived from the original on 2008-03-31.
^ Charles H. Townes – Nobel Lecture Archived 2008-10-11 at the
Wayback Machine.. nobelprize.org
^ "The VLT's Artificial Star". ESO Picture of the Week. Archived from
the original on 3 July 2014. Retrieved 25 June 2014.
^ C. H. Townes. "The first laser". University of Chicago. Archived
from the original on 2008-05-17. Retrieved 2008-05-15.
^ C. H. Townes (2003). "The first laser". In Laura Garwin; Tim
Lincoln. A Century of Nature: Twenty-One Discoveries that Changed
Science and the World. University of Chicago Press. pp. 107–12.
ISBN 0-226-28413-1. Archived from the original on
^ What is a bar code? Archived 2012-04-23 at the Wayback Machine.
^ "How the CD was developed".
BBC News. 2007-08-17. Archived from the
original on 2012-02-18. Retrieved 2007-08-17.
^ J. Wilson & J.F.B. Hawkes (1987). Lasers: Principles and
Applications, Prentice Hall International Series in Optoelectronics.
Prentice Hall. ISBN 0-13-523697-5.
^ a b c D. Atchison & G. Smith (2000).
Optics of the Human Eye.
Elsevier. ISBN 0-7506-3775-7.
^ a b E. R. Kandel; J. H. Schwartz; T. M. Jessell (2000). Principles
of Neural Science (4th ed.). New York: McGraw-Hill.
pp. 507–513. ISBN 0-8385-7701-6.
^ a b D. Meister. "Ophthalmic Lens Design". OptiCampus.com. Archived
from the original on December 27, 2008. Retrieved November 12,
^ J. Bryner (2008-06-02). "Key to All Optical Illusions Discovered".
LiveScience.com. Archived from the original on 2008-09-05.
Geometry of the Vanishing Point Archived 2008-06-22 at the Wayback
Machine. at Convergence Archived 2007-07-13 at the Wayback Machine.
^ "The Moon Illusion Explained" Archived 2015-12-04 at the Wayback
Machine., Don McCready, University of Wisconsin-Whitewater
^ A. K. Jain; M. Figueiredo; J. Zerubia (2001).
Methods in Computer Vision and Pattern Recognition. Springer.
^ a b c d H. D. Young (1992). "36". University
Addison-Wesley. ISBN 0-201-52981-5.
^ P. E. Nothnagle; W. Chambers; M. W. Davidson. "Introduction to
Stereomicroscopy". Nikon MicroscopyU. Archived from the original on
^ Samuel Edward Sheppard & Charles Edward Kenneth Mees (1907).
Investigations on the Theory of the Photographic Process. Longmans,
Green and Co. p. 214.
^ B. J. Suess (2003). Mastering Black-and-White Photography. Allworth
Communications. ISBN 1-58115-306-6.
^ M. J. Langford (2000). Basic Photography. Focal Press.
^ a b Warren, Bruce (2001). Photography. Cengage Learning. p. 71.
ISBN 978-0-7668-1777-7. Archived from the original on
^ Leslie D. Stroebel (1999). View Camera Technique. Focal Press.
^ S. Simmons (1992). Using the View Camera. Amphoto Books. p. 35.
^ Sidney F. Ray (2002). Applied Photographic Optics: Lenses and
Optical Systems for Photography, Film, Video, Electronic and Digital
Imaging. Focal Press. p. 294. ISBN 978-0-240-51540-3.
Archived from the original on 2016-08-19.
^ New York Times Staff (2004). The New York Times Guide to Essential
Knowledge. Macmillan. ISBN 978-0-312-31367-8.
^ R. R. Carlton; A. McKenna Adler (2000). Principles of Radiographic
Imaging: An Art and a Science. Thomson Delmar Learning.
^ W. Crawford (1979). The Keepers of Light: A History and Working
Guide to Early Photographic Processes. Dobbs Ferry, New York: Morgan
& Morgan. p. 20. ISBN 0-87100-158-6.
^ J. M. Cowley (1975).
Diffraction physics. Amsterdam: North-Holland.
^ C. D. Ahrens (1994). Meteorology Today: an introduction to weather,
climate, and the environment (5th ed.). West Publishing Company.
pp. 88–89. ISBN 0-314-02779-3.
^ A. Young. "An Introduction to Mirages". Archived from the original
Born, Max; Wolf, Emil (2002). Principles of Optics. Cambridge
University Press. ISBN 1-139-64340-1.
Hecht, Eugene (2002).
Optics (4 ed.). Addison-Wesley Longman,
Incorporated. ISBN 0-8053-8566-5.
Serway, Raymond A.; Jewett, John W. (2004).
Physics for scientists and
engineers (6, illustrated ed.). Belmont, CA: Thomson-Brooks/Cole.
Tipler, Paul A.; Mosca, Gene (2004).
Physics for Scientists and
Engineers: Electricity, Magnetism, Light, and Elementary Modern
Physics. 2. W. H. Freeman. ISBN 978-0-7167-0810-0.
Lipson, Stephen G.; Lipson, Henry; Tannhauser, David Stefan (1995).
Optical Physics. Cambridge University Press.
Fowles, Grant R. (1975). Introduction to Modern Optics. Courier Dover
Publications. ISBN 0-486-65957-7.
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