The Nature of Light: What is a Photon? (Optical Science and Engineering)
Imagine nonlinear optics pushed to the extreme limit of the quantum world, at the sub-picowatt levels. In this regime, the particle-like nature of light becomes significant, and the most basic concepts of optics and photonics need to be reexamined. The realization of these interactions between individual photons could make light behave akin to conventional particles, such as electrons and atoms. Achieving strong interactions between individual photons has been a goal at the forefront of the quantum-optics research for several decades.
They can be used to realize deterministic two-qubit optical gates for scalable quantum computing and to produce highly-correlated states for high-precision measurements. But perhaps most fascinating, they enable the exploration of new quantum states and phases, similar to those explored in strongly correlated particle systems.
Quantum nonlinear optics QNLO refers this new physical regime, where the optical response of a system is not linear already at the level of single photons. Pinky and the Brain talk about strongly-interacting photons for non-expert. Current ongoing experiments with atomic gases gradually enter the regime of QNLO by using the atoms to mediate effective interactions between individual photons. The interactions are enabled by coherently coupling the photons to high-lying electronic orbitalsknown as Rydberg states. Transitions among Rydberg states have huge electric dipole moments, scaling as n 2.
At these distances, the interaction is of the Van der Walls form and scales as n 11! By 'substantial', we mean that the energy shifts due to the Rydberg-Rydberg interaction are larger than the linewidth of the optical excitation, implying dramatic changes to the optical response. To maintain the nature of the photons while coupling them to Rydberg atoms, we utilize a well-established technique to transform the photons entering the medium into propagating polaritons.
Each polariton is a superposition of a photon and an atomic Rydberg excitation. These so-called dark-state polaritons exhibit several unique properties: their group velocity is much smaller than the speed of light in vacuum owing to their stationary atomic components; their group-velocity dispersion endows them with an effective mass; and their absorption scattering is suppressed despite the light being resonant with the atomic transitions.
To learn more about dark-state polaritons, slow light, and the underlying mechanism of electromagnetically-induced transparency, refer to this review or to our page on polariton experiments. This ensures the ad-hoc excitation of a Rydberg atom per propagating photon. Therefore, individual photons effectively acquire large electric dipoles, long-range interactions, and mass.
They traverse the medium as massive polaritons while experiencing strong, long-range interactions. Several useful concepts have been introduced in the context of coherent Rydberg excitations and interactions. These include the Rydberg blockade, which prevents the excitation of two Rydberg atoms, and the Rydberg macro-atoms, a coherent two-level system comprising many atoms.
The following papers review these concepts and their experimental realizations and discuss the implications for quantum information processing and nonlinear optics:. Pritchard, K. Weatherill, and C. An experimental and theoretical guide to strongly interacting Rydberg gases, J. B: At. Saffman, T. Walker, and K. The atomic cloud is trapped at the intersection of the dipole-trap beams yellow. Photons from the probe beam red transform to polaritons when entering the cloud and transform back when exiting.
Optical non-linearity at the picowatt levels. Two-photon correlation function g 2 in the dissipative regime. The focal length of a simple lens in air is given by the lensmaker's equation. 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 equation.
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 the lens. 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. 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. 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. 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 the waves.
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.
This was derived empirically by Fresnel in , 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 articles on diffraction and Fraunhofer diffraction. More rigorous models, involving the modelling of both electric and magnetic fields of the light wave, are required when dealing with materials whose electric and magnetic properties affect the interaction of light with the material.
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 techniques of Fourier optics which apply many of the same mathematical and analytical techniques used in acoustic engineering and signal processing. 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 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. 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. Since the 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.
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.
More complex designs using multiple layers can achieve low reflectivity over a broad band, or extremely low reflectivity at a single wavelength. 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 slicks. Diffraction is the process by which light interference is most commonly observed. The effect was first described in by Francesco Maria Grimaldi , who also coined the term from the Latin diffringere , 'to break into pieces'. The first physical optics model of diffraction that relied on the Huygens—Fresnel principle was developed in 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 general, the equation takes the form. 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. 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. 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.
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. 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 limit.
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 molecules.
Brillouin scattering occurs when the frequency of light changes due to local changes with time and movements of a dense material.
Photons do the twist, and scientists can now measure it
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.
This is called "anomalous dispersion". The separation of colours by a prism is an example of normal dispersion. Thus, blue light, with its higher refractive index, is bent more strongly than red light, resulting in the well-known rainbow pattern. 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.
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. 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. 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 chirality.
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.
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 this case, one component is zero when the other component is at maximum or minimum amplitude. 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 polarization. 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. 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 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.
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 ". A beam of unpolarised light can be thought of as containing a uniform mixture of linear polarizations at all possible angles. 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. 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. 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.
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. A laser is a device that emits light electromagnetic radiation through a process called stimulated emission. Because the microwave equivalent of the laser, the maser , was developed first, devices that emit microwave and radio frequencies are usually called masers.
The first application of lasers visible in the daily lives of the general population was the supermarket barcode scanner, introduced in 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. The 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 phenomena. Optical communication provides the backbone for both the Internet and modern telephony. 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 transparent media. 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 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 peripheral vision. 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. 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 images. 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 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.
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Cognitive illusions include some which result from the unconscious misapplication of certain optical principles. Another type of optical illusion exploits broken patterns to trick the mind into perceiving symmetries or asymmetries that are not present. Related, but not strictly illusions, are patterns that occur due to the superimposition of periodic structures. 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.
Technology will improve optical computing, telecommunications
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.
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 greater magnification. 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. 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 relation. 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. 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: . 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.
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. The unique optical properties of the atmosphere cause a wide range of spectacular optical phenomena.
The blue colour of the sky is a direct result of 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 geometries. 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 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. Double rainbows are produced by two internal reflections with angular size of From Wikipedia, the free encyclopedia. This article is about the branch of physics. For the book by Sir Isaac Newton, see Opticks.
For other uses, see Optic disambiguation. The branch of physics that studies light. Main article: History of optics. See also: Timeline of electromagnetism and classical optics. Main article: Geometrical optics. Main article: Reflection physics. Diagram of specular reflection. Main article: Refraction.
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Main article: Lens optics. Main article: Physical optics. Main articles: Superposition principle and Interference optics. Main articles: Diffraction and Optical resolution. Main articles: Dispersion optics and Scattering. 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. Main article: Polarization waves. Main articles: Optical physics and Optical engineering. Main article: Laser. Main articles: Human eye and Photometry optics. Main articles: Optical illusions and Perspective graphical. For the visual effects used in film, video, and computer graphics, see visual effects.
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Main article: Science of photography. Main article: Atmospheric optics. Physics portal.
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BBC News. July 1, Archived from the original on February 1, Retrieved Jan 3, Hoad Retrieved Heath A manual of greek mathematics. Courier Dover Publications. Uttal Visual Form Detection in 3-Dimensional Space. Psychology Press. Archived from the original on Elaheh Kheirandish ed. New York: Springer. Mark Smith ed.