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105-634: The upper photo on the right is a 50 times magnification of the combined photomasks used to fabricate the Hughes H4040, the linear silicon photodiode array used in the Thematic Mapper to image the visible bands. Each of the 16 photodiodes is 100 microns square and their separation is 100 microns. There are two rows because it is scanned perpendicular to the lines of diodes and they produce a complete line with no separation. The alignment marks and their layer names can be seen at each end. Each layer

210-402: A Hermitian operator . In 1924, Satyendra Nath Bose derived Planck's law of black-body radiation without using any electromagnetism, but rather by using a modification of coarse-grained counting of phase space . Einstein showed that this modification is equivalent to assuming that photons are rigorously identical and that it implied a "mysterious non-local interaction", now understood as

315-521: A point-like particle since it is absorbed or emitted as a whole by arbitrarily small systems, including systems much smaller than its wavelength, such as an atomic nucleus (≈10 m across) or even the point-like electron . While many introductory texts treat photons using the mathematical techniques of non-relativistic quantum mechanics, this is in some ways an awkward oversimplification, as photons are by nature intrinsically relativistic. Because photons have zero rest mass , no wave function defined for

420-515: A P-type or N-type (respectively) substrate layer, such that the intermediate diffusion layer can be fully depleted of majority carriers, like the base region of a bipolar junction transistor . The PPD (usually PNP) is used in CMOS active-pixel sensors ; a precursor NPNP triple junction variant with the MOS buffer capacitor and the back-light illumination scheme with complete charge transfer and no image lag

525-594: A certain threshold; light of frequency lower than the threshold, no matter how intense, does not initiate the reaction. Similarly, electrons can be ejected from a metal plate by shining light of sufficiently high frequency on it (the photoelectric effect ); the energy of the ejected electron is related only to the light's frequency, not to its intensity. At the same time, investigations of black-body radiation carried out over four decades (1860–1900) by various researchers culminated in Max Planck 's hypothesis that

630-513: A charge is accelerated it emits synchrotron radiation . During a molecular , atomic or nuclear transition to a lower energy level , photons of various energy will be emitted, ranging from radio waves to gamma rays . Photons can also be emitted when a particle and its corresponding antiparticle are annihilated (for example, electron–positron annihilation ). In empty space, the photon moves at c (the speed of light ) and its energy and momentum are related by E = pc , where p

735-467: A choice of measuring either one of two "canonically conjugate" quantities, like the position and the momentum of a particle. According to the uncertainty principle, no matter how the particle is prepared, it is not possible to make a precise prediction for both of the two alternative measurements: if the outcome of the position measurement is made more certain, the outcome of the momentum measurement becomes less so, and vice versa. A coherent state minimizes

840-502: A gauge boson , below.) Einstein's 1905 predictions were verified experimentally in several ways in the first two decades of the 20th century, as recounted in Robert Millikan 's Nobel lecture. However, before Compton's experiment showed that photons carried momentum proportional to their wave number (1922), most physicists were reluctant to believe that electromagnetic radiation itself might be particulate. (See, for example,

945-517: A geometric sum. However, Debye's approach failed to give the correct formula for the energy fluctuations of black-body radiation, which were derived by Einstein in 1909. In 1925, Born , Heisenberg and Jordan reinterpreted Debye's concept in a key way. As may be shown classically, the Fourier modes of the electromagnetic field —a complete set of electromagnetic plane waves indexed by their wave vector k and polarization state—are equivalent to

1050-458: A good PIN diode is so low (<1 nA) that the Johnson–Nyquist noise of the load resistance in a typical circuit often dominates. Avalanche photodiodes are photodiodes with structure optimized for operating with high reverse bias, approaching the reverse breakdown voltage. This allows each photo-generated carrier to be multiplied by avalanche breakdown , resulting in internal gain within

1155-475: A higher energy E i {\displaystyle E_{i}} is proportional to the number N j {\displaystyle N_{j}} of atoms with energy E j {\displaystyle E_{j}} and to the energy density ρ ( ν ) {\displaystyle \rho (\nu )} of ambient photons of that frequency, where B j i {\displaystyle B_{ji}}

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1260-504: A higher energy E i {\displaystyle E_{i}} to a lower energy E j {\displaystyle E_{j}} is where A i j {\displaystyle A_{ij}} is the rate constant for emitting a photon spontaneously , and B i j {\displaystyle B_{ij}} is the rate constant for emissions in response to ambient photons ( induced or stimulated emission ). In thermodynamic equilibrium,

1365-455: A light beam may have mixtures of these two values; a linearly polarized light beam will act as if it were composed of equal numbers of the two possible angular momenta. The spin angular momentum of light does not depend on its frequency, and was experimentally verified by C. V. Raman and S. Bhagavantam in 1931. The collision of a particle with its antiparticle can create photons. In free space at least two photons must be created since, in

1470-600: A paper in which he proposed that many light-related phenomena—including black-body radiation and the photoelectric effect —would be better explained by modelling electromagnetic waves as consisting of spatially localized, discrete energy quanta. He called these a light quantum (German: ein Lichtquant ). The name photon derives from the Greek word for light, φῶς (transliterated phôs ). Arthur Compton used photon in 1928, referring to Gilbert N. Lewis , who coined

1575-473: A photo shows the Hughes (IPD) Newsletter from August 1978 highlighting the second level of aluminium that formed the light shield and set the aperture locations. It was a necessary requirement to prevent this shield from shorting out the lower layer aluminium leads to the photodiodes through defects and pinholes given that this layer was a large sheet over everything. Added ref 3. . The Thematic Mapper has become

1680-555: A photodiode include spectral responsivity, dark current, response time and noise-equivalent power. When a photodiode is used in an optical communication system, all these parameters contribute to the sensitivity of the optical receiver which is the minimum input power required for the receiver to achieve a specified bit error rate . P–n photodiodes are used in similar applications to other photodetectors , such as photoconductors , charge-coupled devices (CCD), and photomultiplier tubes. They may be used to generate an output which

1785-459: A photon can have all the properties familiar from wave functions in non-relativistic quantum mechanics. In order to avoid these difficulties, physicists employ the second-quantized theory of photons described below, quantum electrodynamics , in which photons are quantized excitations of electromagnetic modes. Another difficulty is finding the proper analogue for the uncertainty principle , an idea frequently attributed to Heisenberg, who introduced

1890-399: A photon is calculated by equations that describe waves. This combination of aspects is known as wave–particle duality . For example, the probability distribution for the location at which a photon might be detected displays clearly wave-like phenomena such as diffraction and interference . A single photon passing through a double slit has its energy received at a point on the screen with

1995-473: A position sensor , for example as part of an angle sensor. A two-dimensional array is used in image sensors and optical mice . In some applications, photodiode arrays allow for high-speed parallel readout, as opposed to integrating scanning electronics as in a charge-coupled device (CCD) or CMOS sensor . The optical mouse chip shown in the photo has parallel (not multiplexed) access to all 16 photodiodes in its 4 × 4 array. The passive-pixel sensor (PPS)

2100-402: A probability distribution given by its interference pattern determined by Maxwell's wave equations . However, experiments confirm that the photon is not a short pulse of electromagnetic radiation; a photon's Maxwell waves will diffract, but photon energy does not spread out as it propagates, nor does this energy divide when it encounters a beam splitter . Rather, the received photon acts like

2205-410: A relatively simple assumption. He decomposed the electromagnetic field in a cavity into its Fourier modes , and assumed that the energy in any mode was an integer multiple of h ν {\displaystyle h\nu } , where ν {\displaystyle \nu } is the frequency of the electromagnetic mode. Planck's law of black-body radiation follows immediately as

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2310-497: A semi-classical, statistical treatment of photons and atoms, which implies a link between the rates at which atoms emit and absorb photons. The condition follows from the assumption that functions of the emission and absorption of radiation by the atoms are independent of each other, and that thermal equilibrium is made by way of the radiation's interaction with the atoms. Consider a cavity in thermal equilibrium with all parts of itself and filled with electromagnetic radiation and that

2415-450: A semiclassical approach, and, in 1927, succeeded in deriving all the rate constants from first principles within the framework of quantum theory. Dirac's work was the foundation of quantum electrodynamics, i.e., the quantization of the electromagnetic field itself. Dirac's approach is also called second quantization or quantum field theory ; earlier quantum mechanical treatments only treat material particles as quantum mechanical, not

2520-460: A set of uncoupled simple harmonic oscillators . Treated quantum mechanically, the energy levels of such oscillators are known to be E = n h ν {\displaystyle E=nh\nu } , where ν {\displaystyle \nu } is the oscillator frequency. The key new step was to identify an electromagnetic mode with energy E = n h ν {\displaystyle E=nh\nu } as

2625-468: A source of light which is part of the same circuit or system. A photodiode is often combined into a single component with an emitter of light, usually a light-emitting diode (LED), either to detect the presence of a mechanical obstruction to the beam ( slotted optical switch ) or to couple two digital or analog circuits while maintaining extremely high electrical isolation between them, often for safety ( optocoupler ). The combination of LED and photodiode

2730-399: A state with n {\displaystyle n} photons, each of energy h ν {\displaystyle h\nu } . This approach gives the correct energy fluctuation formula. Dirac took this one step further. He treated the interaction between a charge and an electromagnetic field as a small perturbation that induces transitions in the photon states, changing

2835-414: A unit related to the illumination of the eye and the resulting sensation of light and was used later in a physiological context. Although Wolfers's and Lewis's theories were contradicted by many experiments and never accepted, the new name was adopted by most physicists very soon after Compton used it. In physics, a photon is usually denoted by the symbol γ (the Greek letter gamma ). This symbol for

2940-879: A useful tool in the study of albedo and its relationship to global warming and climate change . The TM on the Landsat 5 has proven useful in determining the amount of ice loss on glaciers due to melting. Landsat 7 carries an enhanced TM sensor known as the Enhanced Thematic Mapper Plus (ETM+). 2. J. L. Engle and O. Weinstein, "The Thematic Mapper---An Overview," in IEEE Transactions on Geoscience and Remote Sensing , vol. GE-21, no. 3, pp. 258–265, July 1983, doi: 10.1109/TGRS.1983.350551. 3. Letter to Professor William Thompson 7/4/2021 Describing fabrication of H4040 photodiode array for Thematic Mapper Photodiode A photodiode

3045-422: Is a PIN structure or p–n junction . When a photon of sufficient energy strikes the diode, it creates an electron – hole pair. This mechanism is also known as the inner photoelectric effect . If the absorption occurs in the junction's depletion region , or one diffusion length away from it, these carriers are swept from the junction by the built-in electric field of the depletion region. Thus holes move toward

3150-553: Is a different color. The pink layer is a second layer of aluminium acting as an aperture. The openings had to be 100u square exactly. The exact dimensions were required in order to achieve a 30 meter resolution on the ground. A set of four of these were fabricated and the fabrication process documented to NASA requirements and verified the dimensions as part of my employment at Hughes Aircraft Company's Industrial Products Division in Carlsbad California in 1978. The challenge

3255-491: Is a semiconductor diode sensitive to photon radiation, such as visible light, infrared or ultraviolet radiation, X-rays and gamma rays . It produces an electrical current when it absorbs photons. This can be used for detection and measurement applications, or for the generation of electrical power in solar cells . Photodiodes are used in a wide range of applications throughout the electromagnetic spectrum from visible light photocells to gamma ray spectrometers. A photodiode

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3360-438: Is a two-in-one power source plus transistor device that runs on solar energy by exploiting a memresistive effect in the flow of photogenerated carriers. The material used to make a photodiode is critical to defining its properties, because only photons with sufficient energy to excite electrons across the material's bandgap will produce significant photocurrents. Materials commonly used to produce photodiodes are listed in

3465-434: Is a type of photodiode array. It was the precursor to the active-pixel sensor (APS). A passive-pixel sensor consists of passive pixels which are read out without amplification , with each pixel consisting of a photodiode and a MOSFET switch. In a photodiode array, pixels contain a p–n junction , integrated capacitor , and MOSFETs as selection transistors . A photodiode array was proposed by G. Weckler in 1968, predating

3570-751: Is also used in many sensor systems to characterize different types of products based on their optical absorbance . Photodiodes are often used for accurate measurement of light intensity in science and industry. They generally have a more linear response than photoconductors. They are also widely used in various medical applications, such as detectors for computed tomography (coupled with scintillators ), instruments to analyze samples ( immunoassay ), and pulse oximeters . PIN diodes are much faster and more sensitive than p–n junction diodes, and hence are often used for optical communications and in lighting regulation. P–n photodiodes are not used to measure extremely low light intensities. Instead, if high sensitivity

3675-619: Is avoided by encapsulating devices in opaque housings. If these housings are not completely opaque to high-energy radiation (ultraviolet, X-rays, gamma rays), diodes, transistors and ICs can malfunction due to induced photo-currents. Background radiation from the packaging is also significant. Radiation hardening mitigates these effects. In some cases, the effect is actually wanted, for example to use LEDs as light-sensitive devices (see LED as light sensor ) or even for energy harvesting , then sometimes called light-emitting and light-absorbing diodes (LEADs). Critical performance parameters of

3780-738: Is dependent upon the illumination (analog for measurement), or to change the state of circuitry (digital, either for control and switching or for digital signal processing). Photodiodes are used in consumer electronics devices such as compact disc players, smoke detectors , medical devices and the receivers for infrared remote control devices used to control equipment from televisions to air conditioners. For many applications either photodiodes or photoconductors may be used. Either type of photosensor may be used for light measurement, as in camera light meters, or to respond to light levels, as in switching on street lighting after dark. Photosensors of all types may be used to respond to incident light or to

3885-479: Is needed, avalanche photodiodes , intensified charge-coupled devices or photomultiplier tubes are used for applications such as astronomy , spectroscopy , night vision equipment and laser rangefinding . Advantages compared to photomultipliers : Disadvantages compared to photomultipliers : The pinned photodiode (PPD) has a shallow implant (P+ or N+) in N-type or P-type diffusion layer, respectively, over

3990-483: Is not quantized, but matter appears to obey the laws of quantum mechanics . Although the evidence from chemical and physical experiments for the existence of photons was overwhelming by the 1970s, this evidence could not be considered as absolutely definitive; since it relied on the interaction of light with matter, and a sufficiently complete theory of matter could in principle account for the evidence. Nevertheless, all semiclassical theories were refuted definitively in

4095-509: Is the gauge boson for electromagnetism , and therefore all other quantum numbers of the photon (such as lepton number , baryon number , and flavour quantum numbers ) are zero. Also, the photon obeys Bose–Einstein statistics , and not Fermi–Dirac statistics . That is, they do not obey the Pauli exclusion principle and more than one can occupy the same bound quantum state. Photons are emitted in many natural processes. For example, when

4200-414: Is the magnitude of the momentum vector p . This derives from the following relativistic relation, with m = 0 : The energy and momentum of a photon depend only on its frequency ( ν {\displaystyle \nu } ) or inversely, its wavelength ( λ ): where k is the wave vector , where Since p {\displaystyle {\boldsymbol {p}}} points in

4305-512: Is the rate constant for absorption. For the reverse process, there are two possibilities: spontaneous emission of a photon, or the emission of a photon initiated by the interaction of the atom with a passing photon and the return of the atom to the lower-energy state. Following Einstein's approach, the corresponding rate R i j {\displaystyle R_{ij}} for the emission of photons of frequency ν {\displaystyle \nu } and transition from

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4410-427: Is the photon's frequency . The photon has no electric charge , is generally considered to have zero rest mass and is a stable particle . The experimental upper limit on the photon mass is very small, on the order of 10 kg; its lifetime would be more than 10 years. For comparison the age of the universe is about 1.38 × 10 years. In a vacuum, a photon has two possible polarization states. The photon

4515-405: The anode , and electrons toward the cathode , and a photocurrent is produced. The total current through the photodiode is the sum of the dark current (current that is passed in the absence of light) and the photocurrent, so the dark current must be minimized to maximize the sensitivity of the device. To first order, for a given spectral distribution, the photocurrent is linearly proportional to

4620-499: The center of momentum frame , the colliding antiparticles have no net momentum, whereas a single photon always has momentum (determined by the photon's frequency or wavelength, which cannot be zero). Hence, conservation of momentum (or equivalently, translational invariance ) requires that at least two photons are created, with zero net momentum. The energy of the two photons, or, equivalently, their frequency, may be determined from conservation of four-momentum . Seen another way,

4725-463: The degeneracy of the state i {\displaystyle i} and that of j {\displaystyle j} , respectively, E i {\displaystyle E_{i}} and E j {\displaystyle E_{j}} their energies, k {\displaystyle k} the Boltzmann constant and T {\displaystyle T}

4830-423: The energy of a Maxwellian light wave were localized into point-like quanta that move independently of one another, even if the wave itself is spread continuously over space. In 1909 and 1916, Einstein showed that, if Planck's law regarding black-body radiation is accepted, the energy quanta must also carry momentum p = ⁠ h  / λ  ⁠ , making them full-fledged particles. This photon momentum

4935-406: The field-effect phototransistor (also known as photoFET), is a light-sensitive field-effect transistor. Unlike photobipolar transistors, photoFETs control drain-source current by creating a gate voltage. A solaristor is a two-terminal gate-less phototransistor. A compact class of two-terminal phototransistors or solaristors have been demonstrated in 2018 by ICN2 researchers. The novel concept

5040-444: The irradiance . In photovoltaic mode (zero bias ), photocurrent flows into the anode through a short circuit to the cathode. If the circuit is opened or has a load impedance, restricting the photocurrent out of the device, a voltage builds up in the direction that forward biases the diode, that is, anode positive with respect to cathode. If the circuit is shorted or the impedance is low, a forward current will consume all or some of

5145-411: The probabilistic interpretation of quantum mechanics. It has been applied to photochemistry , high-resolution microscopy , and measurements of molecular distances . Moreover, photons have been studied as elements of quantum computers , and for applications in optical imaging and optical communication such as quantum cryptography . The word quanta (singular quantum, Latin for how much )

5250-407: The probability amplitude of observable events is calculated by summing over all possible intermediate steps, even ones that are unphysical; hence, virtual photons are not constrained to satisfy E = p c {\displaystyle E=pc} , and may have extra polarization states; depending on the gauge used, virtual photons may have three or four polarization states, instead of

5355-426: The speed of light measured in vacuum. The photon belongs to the class of boson particles. As with other elementary particles, photons are best explained by quantum mechanics and exhibit wave–particle duality , their behavior featuring properties of both waves and particles . The modern photon concept originated during the first two decades of the 20th century with the work of Albert Einstein , who built upon

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5460-415: The 1970s and 1980s by photon-correlation experiments. Hence, Einstein's hypothesis that quantization is a property of light itself is considered to be proven. Photons obey the laws of quantum mechanics, and so their behavior has both wave-like and particle-like aspects. When a photon is detected by a measuring instrument, it is registered as a single, particulate unit. However, the probability of detecting

5565-536: The CCD. This was the basis for the PPS. The noise of photodiode arrays is sometimes a limitation to performance. It was not possible to fabricate active pixel sensors with a practical pixel size in the 1970s, due to limited microlithography technology at the time. [REDACTED]  This article incorporates public domain material from Federal Standard 1037C . General Services Administration . Archived from

5670-548: The Maxwell theory of light allows for all possible energies of electromagnetic radiation, most physicists assumed initially that the energy quantization resulted from some unknown constraint on the matter that absorbs or emits the radiation. In 1905, Einstein was the first to propose that energy quantization was a property of electromagnetic radiation itself. Although he accepted the validity of Maxwell's theory, Einstein pointed out that many anomalous experiments could be explained if

5775-470: The Nobel lectures of Wien , Planck and Millikan.) Instead, there was a widespread belief that energy quantization resulted from some unknown constraint on the matter that absorbed or emitted radiation. Attitudes changed over time. In part, the change can be traced to experiments such as those revealing Compton scattering , where it was much more difficult not to ascribe quantization to light itself to explain

5880-600: The Thematic Mapper. The final assembly or the TM Focal Plane without filers is shown in the second photo to the right. They flew in Landsat 4 and for 20 years maintained operation. Also shown on the right is a letter of acknowledgement from Hughes Aircraft Company's Industrial Products Division (IPD) on the invention of the LPCVDs silicon nitride system that made the Thematic Mapper diode arrays possible. Additionally

5985-509: The anode. This reduces the response time because the additional reverse bias increases the width of the depletion layer, which decreases the junction's capacitance and increases the region with an electric field that will cause electrons to be quickly collected. The reverse bias also creates dark current without much change in the photocurrent. Although this mode is faster, the photoconductive mode can exhibit more electronic noise due to dark current or avalanche effects. The leakage current of

6090-438: The atoms can emit and absorb that radiation. Thermal equilibrium requires that the energy density ρ ( ν ) {\displaystyle \rho (\nu )} of photons with frequency ν {\displaystyle \nu } (which is proportional to their number density ) is, on average, constant in time; hence, the rate at which photons of any particular frequency are emitted must equal

6195-530: The average across many interactions between matter and radiation. However, refined Compton experiments showed that the conservation laws hold for individual interactions. Accordingly, Bohr and his co-workers gave their model "as honorable a funeral as possible". Nevertheless, the failures of the BKS model inspired Werner Heisenberg in his development of matrix mechanics . A few physicists persisted in developing semiclassical models in which electromagnetic radiation

6300-502: The base–collector junction are injected into the base, and this photodiode current is amplified by the transistor's current gain β (or h fe ). If the base and collector leads are used and the emitter is left unconnected, the phototransistor becomes a photodiode. While phototransistors have a higher responsivity for light they are not able to detect low levels of light any better than photodiodes. Phototransistors also have significantly longer response times. Another type of phototransistor,

6405-486: The coefficients A i j {\displaystyle A_{ij}} , B j i {\displaystyle B_{ji}} and B i j {\displaystyle B_{ij}} once physicists had obtained "mechanics and electrodynamics modified to accommodate the quantum hypothesis". Not long thereafter, in 1926, Paul Dirac derived the B i j {\displaystyle B_{ij}} rate constants by using

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6510-418: The concept in analyzing a thought experiment involving an electron and a high-energy photon . However, Heisenberg did not give precise mathematical definitions of what the "uncertainty" in these measurements meant. The precise mathematical statement of the position–momentum uncertainty principle is due to Kennard , Pauli , and Weyl . The uncertainty principle applies to situations where an experimenter has

6615-466: The direction of the photon's propagation, the magnitude of its momentum is The photon also carries spin angular momentum , which is related to photon polarization . (Beams of light also exhibit properties described as orbital angular momentum of light ). The angular momentum of the photon has two possible values, either +ħ or −ħ . These two possible values correspond to the two possible pure states of circular polarization . Collections of photons in

6720-484: The electric field of an atomic nucleus. The classical formulae for the energy and momentum of electromagnetic radiation can be re-expressed in terms of photon events. For example, the pressure of electromagnetic radiation on an object derives from the transfer of photon momentum per unit time and unit area to that object, since pressure is force per unit area and force is the change in momentum per unit time. Current commonly accepted physical theories imply or assume

6825-450: The electromagnetic field. Einstein was troubled by the fact that his theory seemed incomplete, since it did not determine the direction of a spontaneously emitted photon. A probabilistic nature of light-particle motion was first considered by Newton in his treatment of birefringence and, more generally, of the splitting of light beams at interfaces into a transmitted beam and a reflected beam. Newton hypothesized that hidden variables in

6930-487: The electromagnetic wave, Δ N {\displaystyle \Delta N} , and the uncertainty in the phase of the wave, Δ ϕ {\displaystyle \Delta \phi } . However, this cannot be an uncertainty relation of the Kennard–Pauli–Weyl type, since unlike position and momentum, the phase ϕ {\displaystyle \phi } cannot be represented by

7035-441: The energy of any system that absorbs or emits electromagnetic radiation of frequency ν is an integer multiple of an energy quantum E = hν . As shown by Albert Einstein , some form of energy quantization must be assumed to account for the thermal equilibrium observed between matter and electromagnetic radiation ; for this explanation of the photoelectric effect, Einstein received the 1921 Nobel Prize in physics. Since

7140-501: The final blow to particle models of light. The Maxwell wave theory , however, does not account for all properties of light. The Maxwell theory predicts that the energy of a light wave depends only on its intensity , not on its frequency ; nevertheless, several independent types of experiments show that the energy imparted by light to atoms depends only on the light's frequency, not on its intensity. For example, some chemical reactions are provoked only by light of frequency higher than

7245-418: The galactic vector potential . Although the galactic vector potential is large because the galactic magnetic field exists on great length scales, only the magnetic field would be observable if the photon is massless. In the case that the photon has mass, the mass term ⁠ 1 / 2 ⁠ m A μ A would affect the galactic plasma. The fact that no such effects are seen implies an upper bound on

7350-661: The galactic vector potential have been shown to be model-dependent. If the photon mass is generated via the Higgs mechanism then the upper limit of m ≲ 10  eV/ c from the test of Coulomb's law is valid. In most theories up to the eighteenth century, light was pictured as being made of particles. Since particle models cannot easily account for the refraction , diffraction and birefringence of light, wave theories of light were proposed by René Descartes (1637), Robert Hooke (1665), and Christiaan Huygens (1678); however, particle models remained dominant, chiefly due to

7455-404: The influence of Isaac Newton . In the early 19th century, Thomas Young and August Fresnel clearly demonstrated the interference and diffraction of light, and by 1850 wave models were generally accepted. James Clerk Maxwell 's 1865 prediction that light was an electromagnetic wave – which was confirmed experimentally in 1888 by Heinrich Hertz 's detection of radio waves – seemed to be

7560-455: The light particle determined which of the two paths a single photon would take. Similarly, Einstein hoped for a more complete theory that would leave nothing to chance, beginning his separation from quantum mechanics. Ironically, Max Born 's probabilistic interpretation of the wave function was inspired by Einstein's later work searching for a more complete theory. In 1910, Peter Debye derived Planck's law of black-body radiation from

7665-418: The number of atoms in state i {\displaystyle i} and those in state j {\displaystyle j} must, on average, be constant; hence, the rates R j i {\displaystyle R_{ji}} and R i j {\displaystyle R_{ij}} must be equal. Also, by arguments analogous to the derivation of Boltzmann statistics ,

7770-509: The numbers of photons in the modes, while conserving energy and momentum overall. Dirac was able to derive Einstein's A i j {\displaystyle A_{ij}} and B i j {\displaystyle B_{ij}} coefficients from first principles, and showed that the Bose–Einstein statistics of photons is a natural consequence of quantizing the electromagnetic field correctly (Bose's reasoning went in

7875-476: The observed results. Even after Compton's experiment, Niels Bohr , Hendrik Kramers and John Slater made one last attempt to preserve the Maxwellian continuous electromagnetic field model of light, the so-called BKS theory . An important feature of the BKS theory is how it treated the conservation of energy and the conservation of momentum . In the BKS theory, energy and momentum are only conserved on

7980-472: The opposite direction; he derived Planck's law of black-body radiation by assuming B–E statistics). In Dirac's time, it was not yet known that all bosons, including photons, must obey Bose–Einstein statistics. Dirac's second-order perturbation theory can involve virtual photons , transient intermediate states of the electromagnetic field; the static electric and magnetic interactions are mediated by such virtual photons. In such quantum field theories ,

8085-410: The original on 2022-01-22. Photon A photon (from Ancient Greek φῶς , φωτός ( phôs, phōtós )  'light') is an elementary particle that is a quantum of the electromagnetic field , including electromagnetic radiation such as light and radio waves , and the force carrier for the electromagnetic force . Photons are massless particles that always move at

8190-405: The overall uncertainty as far as quantum mechanics allows. Quantum optics makes use of coherent states for modes of the electromagnetic field. There is a tradeoff, reminiscent of the position–momentum uncertainty relation, between measurements of an electromagnetic wave's amplitude and its phase. This is sometimes informally expressed in terms of the uncertainty in the number of photons present in

8295-426: The photocurrent. This mode exploits the photovoltaic effect , which is the basis for solar cells – a traditional solar cell is just a large area photodiode. For optimum power output, the photovoltaic cell will be operated at a voltage that causes only a small forward current compared to the photocurrent. In photoconductive mode the diode is reverse biased , that is, with the cathode driven positive with respect to

8400-464: The photodiode, which increases the effective responsivity of the device. A phototransistor is a light-sensitive transistor. A common type of phototransistor, the bipolar phototransistor , is in essence a bipolar transistor encased in a transparent case so that light can reach the base–collector junction . It was invented by John N. Shive at Bell Labs in 1948 but it was not announced until 1950. The electrons that are generated by photons in

8505-400: The photon can be considered as its own antiparticle (thus an "antiphoton" is simply a normal photon with opposite momentum, equal polarization, and 180° out of phase). The reverse process, pair production , is the dominant mechanism by which high-energy photons such as gamma rays lose energy while passing through matter. That process is the reverse of "annihilation to one photon" allowed in

8610-472: The photon mass of m < 3 × 10  eV/ c . The galactic vector potential can also be probed directly by measuring the torque exerted on a magnetized ring. Such methods were used to obtain the sharper upper limit of 1.07 × 10  eV/ c (the equivalent of 10   daltons ) given by the Particle Data Group . These sharp limits from the non-observation of the effects caused by

8715-467: The photon probably derives from gamma rays , which were discovered in 1900 by Paul Villard , named by Ernest Rutherford in 1903, and shown to be a form of electromagnetic radiation in 1914 by Rutherford and Edward Andrade . In chemistry and optical engineering , photons are usually symbolized by hν , which is the photon energy , where h is the Planck constant and the Greek letter ν ( nu )

8820-473: The photon to be strictly massless. If photons were not purely massless, their speeds would vary with frequency, with lower-energy (redder) photons moving slightly slower than higher-energy photons. Relativity would be unaffected by this; the so-called speed of light, c , would then not be the actual speed at which light moves, but a constant of nature which is the upper bound on speed that any object could theoretically attain in spacetime. Thus, it would still be

8925-444: The rate at which they are absorbed . Einstein began by postulating simple proportionality relations for the different reaction rates involved. In his model, the rate R j i {\displaystyle R_{ji}} for a system to absorb a photon of frequency ν {\displaystyle \nu } and transition from a lower energy E j {\displaystyle E_{j}} to

9030-524: The ratio of N i {\displaystyle N_{i}} and N j {\displaystyle N_{j}} is g i / g j exp ⁡ ( E j − E i ) / ( k T ) , {\displaystyle g_{i}/g_{j}\exp {(E_{j}-E_{i})/(kT)},} where g i {\displaystyle g_{i}} and g j {\displaystyle g_{j}} are

9135-405: The requirement for a symmetric quantum mechanical state . This work led to the concept of coherent states and the development of the laser. In the same papers, Einstein extended Bose's formalism to material particles (bosons) and predicted that they would condense into their lowest quantum state at low enough temperatures; this Bose–Einstein condensation was observed experimentally in 1995. It

9240-470: The research of Max Planck . While Planck was trying to explain how matter and electromagnetic radiation could be in thermal equilibrium with one another, he proposed that the energy stored within a material object should be regarded as composed of an integer number of discrete, equal-sized parts. To explain the photoelectric effect , Einstein introduced the idea that light itself is made of discrete units of energy. In 1926, Gilbert N. Lewis popularized

9345-482: The signal carriers could be transferred from the photodiode to the CCD. This led to their invention of the pinned photodiode, a photodetector structure with low lag, low noise , high quantum efficiency and low dark current . It was first publicly reported by Teranishi and Ishihara with A. Kohono, E. Oda and K. Arai in 1982, with the addition of an anti-blooming structure. The new photodetector structure invented by Sony in 1975, developed by NEC in 1982 by Kodak in 1984

9450-465: The speed of light. If Coulomb's law is not exactly valid, then that would allow the presence of an electric field to exist within a hollow conductor when it is subjected to an external electric field. This provides a means for precision tests of Coulomb's law . A null result of such an experiment has set a limit of m ≲ 10  eV/ c . Sharper upper limits on the mass of light have been obtained in experiments designed to detect effects caused by

9555-412: The speed of spacetime ripples ( gravitational waves and gravitons ), but it would not be the speed of photons. If a photon did have non-zero mass, there would be other effects as well. Coulomb's law would be modified and the electromagnetic field would have an extra physical degree of freedom . These effects yield more sensitive experimental probes of the photon mass than the frequency dependence of

9660-501: The summation as well; for example, two photons may interact indirectly through virtual electron – positron pairs . Such photon–photon scattering (see two-photon physics ), as well as electron–photon scattering, is meant to be one of the modes of operations of the planned particle accelerator, the International Linear Collider . In modern physics notation, the quantum state of the electromagnetic field

9765-587: The system's temperature . From this, it is readily derived that g i B i j = g j B j i {\displaystyle g_{i}B_{ij}=g_{j}B_{ji}} and The A i j {\displaystyle A_{ij}} and B i j {\displaystyle B_{ij}} are collectively known as the Einstein coefficients . Einstein could not fully justify his rate equations, but claimed that it should be possible to calculate

9870-473: The table below. Because of their greater bandgap, silicon-based photodiodes generate less noise than germanium-based photodiodes. Binary materials, such as MoS 2 , and graphene emerged as new materials for the production of photodiodes. Any p–n junction, if illuminated, is potentially a photodiode. Semiconductor devices such as diodes, transistors and ICs contain p–n junctions, and will not function correctly if they are illuminated by unwanted light. This

9975-664: The term photon for these energy units. Subsequently, many other experiments validated Einstein's approach. In the Standard Model of particle physics , photons and other elementary particles are described as a necessary consequence of physical laws having a certain symmetry at every point in spacetime . The intrinsic properties of particles, such as charge , mass , and spin , are determined by gauge symmetry . The photon concept has led to momentous advances in experimental and theoretical physics, including lasers , Bose–Einstein condensation , quantum field theory , and

10080-578: The term in a letter to Nature on 18 December 1926. The same name was used earlier but was never widely adopted before Lewis: in 1916 by the American physicist and psychologist Leonard T. Troland , in 1921 by the Irish physicist John Joly , in 1924 by the French physiologist René Wurmser (1890–1993), and in 1926 by the French physicist Frithiof Wolfers (1891–1971). The name was suggested initially as

10185-423: The two states of real photons. Although these transient virtual photons can never be observed, they contribute measurably to the probabilities of observable events. Indeed, such second-order and higher-order perturbation calculations can give apparently infinite contributions to the sum. Such unphysical results are corrected for using the technique of renormalization . Other virtual particles may contribute to

10290-419: Was an atmospheric deposition system that basically burned silane (SiH4) in the presence of ammonia in a horizontal tube heated to about 850 °C. But that process yielded a smoky film that varied significantly over the silicon wafer and the diode array. So with the help of a workmate who had invented low pressure (LPCVD) polysilicon deposition at Motorola a few years earlier a low pressure silicon nitride system

10395-428: Was built using silane and ammonia to produce the precisely tunable and uniform thicknesses needed at each of the bands. Without that innovation there would have been no TM. The boron diffused photodiodes had to have very low dark current and high photosensitivity in order to meet the imager specifications. The large crosses visible on the pattern were used when the different arrays were aligned together at final assembly in

10500-745: Was given the name "pinned photodiode" (PPD) by B.C. Burkey at Kodak in 1984. In 1987, the PPD began to be incorporated into most CCD sensors, becoming a fixture in consumer electronic video cameras and then digital still cameras . A CMOS image sensor with a low-voltage-PPD technology was first fabricated in 1995 by a joint JPL and Kodak team. The CMOS sensor with PPD technology was further advanced and refined by R.M. Guidash in 1997, K. Yonemoto and H. Sumi in 2000, and I. Inoue in 2003. This led to CMOS sensors achieve imaging performance on par with CCD sensors, and later exceeding CCD sensors. A one-dimensional array of hundreds or thousands of photodiodes can be used as

10605-411: Was invented by Sony in 1975. This scheme was widely used in many applications of charge transfer devices. Early charge-coupled device image sensors suffered from shutter lag . This was largely explained with the re-invention of the pinned photodiode. It was developed by Nobukazu Teranishi , Hiromitsu Shiraki and Yasuo Ishihara at NEC in 1980. Sony in 1975 recognized that lag can be eliminated if

10710-441: Was later used by Lene Hau to slow, and then completely stop, light in 1999 and 2001. The modern view on this is that photons are, by virtue of their integer spin, bosons (as opposed to fermions with half-integer spin). By the spin-statistics theorem , all bosons obey Bose–Einstein statistics (whereas all fermions obey Fermi–Dirac statistics ). In 1916, Albert Einstein showed that Planck's radiation law could be derived from

10815-499: Was observed experimentally by Arthur Compton , for which he received the Nobel Prize in 1927. The pivotal question then, was how to unify Maxwell's wave theory of light with its experimentally observed particle nature. The answer to this question occupied Albert Einstein for the rest of his life, and was solved in quantum electrodynamics and its successor, the Standard Model . (See § Quantum field theory and § As

10920-423: Was to customize each of these for one of the narrow visible bands that were required. To do that the thickness of the silicon nitride antireflective layer had to meet a precise target, for example, for one band the target was 120 nm while the next band required 130 nm. In addition all of the 16 photodiodes in the array had to have the same thickness. At the time all that was available to manufacture this film

11025-537: Was used before 1900 to mean particles or amounts of different quantities , including electricity . In 1900, the German physicist Max Planck was studying black-body radiation , and he suggested that the experimental observations, specifically at shorter wavelengths , would be explained if the energy stored within a molecule was a "discrete quantity composed of an integral number of finite equal parts", which he called "energy elements". In 1905, Albert Einstein published

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