Physical optics

Physical optics is used to explain effects such as diffraction

Branch of optics that studies interference, diffraction, polarization, and other phenomena for which the ray approximation of geometric optics is not valid.

- Physical optics

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Ray (optics)

Idealized geometrical model of light, obtained by choosing a curve that is perpendicular to the wavefronts of the actual light, and that points in the direction of energy flow.

Diagram of rays at a surface, where is the angle of refraction.
Simple ray diagram showing typical chief and marginal rays
Rays and wavefronts

Ray optics or geometrical optics does not describe phenomena such as diffraction, which require wave optics theory.


Branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it.

The Nimrud lens
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.
The first treatise about optics by Johannes Kepler, Ad Vitellionem paralipomena quibus astronomiae pars optica traditur (1604)
Cover of the first edition of Newton's Opticks (1704)
Geometry of reflection and refraction of light rays
Diagram of specular reflection
Illustration of Snell's Law for the case n1 < n2, such as air/water interface
A ray tracing diagram for a converging lens.
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.
When oil or fuel is spilled, colourful patterns are formed by thin-film interference.
Conceptual animation of light dispersion through a prism. High frequency (blue) light is deflected the most, and low frequency (red) the least.
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 group velocity).
Linear polarization diagram
Circular polarization diagram
Elliptical polarization diagram
A polariser changing the orientation of linearly polarised light. In this picture, θ1 – θ0 = θi.
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.
Experiments such as this one with high-power lasers are part of the modern optics research.
VLT's laser guide star
Model of a human eye. Features mentioned in this article are 1. vitreous humour 3. ciliary muscle, 6. pupil, 7. anterior chamber, 8. cornea, 10. lens cortex, 22. optic nerve, 26. fovea, 30. retina
The Ponzo Illusion relies on the fact that parallel lines appear to converge as they approach infinity.
Illustrations of various optical instruments from the 1728 Cyclopaedia
Photograph taken with aperture 32
Photograph taken with aperture 5
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.

Physical optics is a more comprehensive model of light, which includes wave effects such as diffraction and interference that cannot be accounted for in geometric optics.

Coherence theory (optics)

Various examples of physical phenomena

In physics, coherence theory is the study of optical effects arising from partially coherent light and radio sources.

David Brewster

British scientist, inventor, author, and academic administrator.

Inner picture of a cigar box from the early 1900s with a portrait of Brewster.
The Brewster stereoscope, 1849.
Treatise on new philosophical instruments for various purposes in the arts and sciences, 1813
Calvert Jones, Lady Brewster (Jane Kirk Purnell), Mrs. Jones, David Brewster and Miss Parnell (seated)
Street sign in Kings Buildings, Edinburgh to the memory of David Brewster

In science he is principally remembered for his experimental work in physical optics, mostly concerned with the study of the polarization of light and including the discovery of Brewster's angle.

Double-slit experiment

Demonstration that light and matter can display characteristics of both classically defined waves and particles; moreover, it displays the fundamentally probabilistic nature of quantum mechanical phenomena.

Same double-slit assembly (0.7 mm between slits); in top image, one slit is closed. In the single-slit image, a diffraction pattern (the faint spots on either side of the main band) forms due to the nonzero width of the slit. This diffraction pattern is also seen in the double-slit image, but with many smaller interference fringes.
Buildup of interference pattern from individual particle detections
Photons in a Mach–Zehnder interferometer exhibit wave-like interference and particle-like detection at single-photon detectors.
A diagram of Wheeler's delayed choice experiment, showing the principle of determining the path of the photon after it passes through the slit
A laboratory double-slit assembly; distance between top posts approximately 2.5 cm (one inch).
Near-field intensity distribution patterns for plasmonic slits with equal widths (A) and non-equal widths (B).
Two-slit diffraction pattern by a plane wave
Photo of the double-slit interference of sunlight.
Two slits are illuminated by a plane wave.
One of an infinite number of equally likely paths used in the Feynman path integral (see also: Wiener process)
An example of the uncertainty principle related to the relational interpretation. The more that is known about the position of a particle, the less is known about the velocity, and vice versa

He believed it demonstrated that the wave theory of light was correct, and his experiment is sometimes referred to as Young's experiment or Young's slits.

History of physics

Branch of science whose primary objects of study are matter and energy.

A Newton's cradle, named after physicist Isaac Newton
Aristotle (384–322 BCE)
The ancient Greek mathematician Archimedes, famous for his ideas regarding fluid mechanics and buoyancy.
The Hindu-Arabic numeral system. The inscriptions on the edicts of Ashoka (3rd century BCE) display this number system being used by the Imperial Mauryas.
Star maps by the 11th-century Chinese polymath Su Song are the oldest known woodblock-printed star maps to have survived to the present day. This example, dated 1092, employs cylindrical projection.
Ibn al-Haytham (c. 965–1040).
A page from al-Khwārizmī's Algebra.
The Polish astronomer Nicolaus Copernicus (1473–1543) is remembered for his development of a heliocentric model of the Solar System.
Galileo Galilei, early proponent of the modern scientific worldview and method (1564–1642)
A composite montage comparing Jupiter (lefthand side) and its four Galilean moons (top to bottom: Io, Europa, Ganymede, Callisto).
René Descartes (1596–1650)
Christiaan Huygens (1629–1695)
Sir Isaac Newton (1642–1727)
Gottfried Leibniz (1646–1716)
Alessandro Volta (1745–1827)
Daniel Bernoulli (1700–1782)
Michael Faraday (1791–1867)
William Thomson (Lord Kelvin) (1824–1907)
James Clerk Maxwell (1831–1879)
Ludwig Boltzmann (1844-1906)
Marie Skłodowska-Curie (1867–1934)
J. J. Thomson (1856–1940) discovered the electron and isotopy and also invented the mass spectrometer. He was awarded the Nobel Prize in Physics in 1906.
Albert Einstein (1879–1955), photographed here in around 1905
Einstein proposed that gravitation is a result of masses (or their equivalent energies) curving ("bending") the spacetime in which they exist, altering the paths they follow within it.
Max Planck (1858–1947)
Werner Heisenberg (1901–1976)
A Feynman diagram representing (left to right) the production of a photon (blue sine wave) from the annihilation of an electron and its complementary antiparticle, the positron. The photon becomes a quark–antiquark pair and a gluon (green spiral) is released.
Richard Feynman's Los Alamos ID badge
The Standard Model.
Chien-Shiung Wu worked on parity violation in 1956 and announced her results in January 1957.
One possible signature of a Higgs boson from a simulated proton–proton collision. It decays almost immediately into two jets of hadrons and two electrons, visible as lines.

Five years after the publication of his Horologium Oscillatorium, Huygens described his wave theory of light.

French Academy of Sciences

Learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French scientific research.

Colbert Presenting the Members of the Royal Academy of Sciences to Louis XIV in 1667, by Henri Testelin; in the background appears the new Paris Observatory
Louis XIV Visiting the Royal Academy of Sciences, (Sébastien Leclerc I, France, 1671)
Illustration from Acta Eruditorum (1737) where was published Machines et inventions approuvées par l'Academie Royale des Sciences
The Institut de France in Paris where the Academy is housed

The civil engineer Augustin-Jean Fresnel entered this competition by submitting a new wave theory of light.

Leonhard Euler

Swiss mathematician, physicist, astronomer, geographer, logician and engineer who founded the studies of graph theory and topology and made pioneering and influential discoveries in many other branches of mathematics such as analytic number theory, complex analysis, and infinitesimal calculus.

Portrait by Jakob Emanuel Handmann (1753)
1957 Soviet Union stamp commemorating the 250th birthday of Euler. The text says: 250 years from the birth of the great mathematician, academician Leonhard Euler.
Stamp of the former German Democratic Republic honoring Euler on the 200th anniversary of his death. Across the centre it shows his polyhedral formula, in English written as "v − e + f = 2".
Euler's grave at the Alexander Nevsky Monastery
Map of Königsberg in Euler's time showing the actual layout of the seven bridges, highlighting the river Pregel and the bridges.
An Euler diagram
Euler portrait on the sixth series of the 10 Franc banknote
Euler portrait on the seventh series of the 10 Franc banknote
Illustration from Solutio problematis... a. 1743 propositi published in Acta Eruditorum, 1744
The title page of Euler's Methodus inveniendi lineas curvas.
Euler's 1760 world map.
Euler's 1753 map of Africa.

His 1740s papers on optics helped ensure that the wave theory of light proposed by Christiaan Huygens would become the dominant mode of thought, at least until the development of the quantum theory of light.

Photoelectric effect

Emission of electrons when electromagnetic radiation, such as light, hits a material.

The emission of electrons from a metal plate caused by light quanta – photons.
Schematic of the experiment to demonstrate the photoelectric effect. Filtered, monochromatic light of a certain wavelength strikes the emitting electrode (E) inside a vacuum tube. The collector electrode (C) is biased to a voltage VC that can be set to attract the emitted electrons, when positive, or prevent any of them from reaching the collector when negative.
Diagram of the maximum kinetic energy as a function of the frequency of light on zinc.
The gold leaf electroscope to demonstrate the photoelectric effect. When the electroscope is negatively charged, there is an excess of electrons and the leaves are separated. If short wavelength, high-frequency light (such as ultraviolet light obtained from an arc lamp, or by burning magnesium, or by using an induction coil between zinc or cadmium terminals to produce sparking) shines on the cap, the electroscope discharges, and the leaves fall limp. If, however, the frequency of the light waves is below the threshold value for the cap, the leaves will not discharge, no matter how long one shines the light at the cap.
Angle-resolved photoemission spectroscopy (ARPES) experiment. Helium discharge lamp shines ultraviolet light onto the sample in ultra-high vacuum. Hemispherical electron analyzer measures the distribution of ejected electrons with respect to energy and momentum.

This appeared to be at odds with Maxwell's wave theory of light, which predicted that the electron energy would be proportional to the intensity of the radiation.

Paradigm shift

Fundamental change in the basic concepts and experimental practices of a.

Kuhn used the duck-rabbit optical illusion, made famous by Wittgenstein, to demonstrate the way in which a paradigm shift could cause one to see the same information in an entirely different way.

The transition in optics from geometrical optics to physical optics with Augustin-Jean Fresnel's wave theory.