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Specific Detectivity
Specific detectivity, or ''D*'', for a photodetector is a figure of merit used to characterize performance, equal to the reciprocal of noise-equivalent power (NEP), normalized per square root of the sensor's area and frequency bandwidth (reciprocal of twice the integration time). Specific detectivity is given by D^*=\frac, where A is the area of the photosensitive region of the detector, \Delta f is the bandwidth, and NEP the noise equivalent power in units It is commonly expressed in ''Jones'' units (cm \cdot \sqrt/ W) in honor of Robert Clark Jones who originally defined it.R. C. Jones, "Proposal of the detectivity D** for detectors limited by radiation noise," ''J. Opt. Soc. Am.'' 50, 1058 (1960), ) Given that noise-equivalent power can be expressed as a function of the responsivity \mathfrak (in units of A/W or V/W) and the noise spectral density S_n (in units of A/Hz^ or V/Hz^) as NEP=\frac, it is common to see the specific detectivity expressed as D^*=\frac. It is ofte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Photodetector
Photodetectors, also called photosensors, are devices that detect light or other forms of electromagnetic radiation and convert it into an electrical signal. They are essential in a wide range of applications, from digital imaging and optical communication to scientific research and industrial automation. Photodetectors can be classified by their mechanism of detection, such as the photoelectric effect, photochemical reactions, or thermal effects, or by performance metrics like spectral response. Common types include photodiodes, phototransistors, and photomultiplier tubes, each suited to specific uses. Solar cells, which convert light into electricity, are also a type of photodetector. This article explores the principles behind photodetectors, their various types, applications, and recent advancements in the field. History The development of photodetectors began with the discovery of the photoelectric effect by Heinrich Hertz in 1887, later explained by Albert Einst ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Figure Of Merit
A figure of merit (FOM) is a performance metric that characterizes the performance of a device, system, or method, relative to its alternatives. Examples *Absolute alcohol content per currency unit in an alcoholic beverage *accurizing, Accuracy of a rifle *Audio amplifier figures of merit such as gain or efficiency *Battery life of a laptop computer New York Times, June 25, 2009 *Calories per serving *Clock rate of a CPU is often given as a figure of merit, but is of limited use in comparing between different architectures. FLOPS may be a better figure, though these too are not completely representative of the performance of a CPU. *Contrast ratio of an LCD *Frequency response of a Loudspeaker, speaker *Fill factor (solar cell), Fill factor of a solar cell *Image resolutio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Noise-equivalent Power
Noise-equivalent power (NEP) is a measure of the sensitivity of a photodetector or detector system. It is defined as the signal power that gives a signal-to-noise ratio of one in a one hertz output bandwidth. An output bandwidth of one hertz is equivalent to half a second of integration time.The factor of one half is explained by the Nyquist–Shannon sampling theorem. The units of NEP are watts per square root hertz. The NEP is equal to the noise amplitude spectral density (expressed in units of \mathrm/\sqrt or \mathrm/\sqrt) divided by the responsivity Responsivity is a measure of the input–output Gain (electronics), gain of a detector system. In the specific case of a photodetector, it measures the electrical output per optical input. A photodetector's responsivity is usually expressed in un ... (expressed in units of \mathrm/\mathrm or \mathrm/\mathrm, respectively). The fundamental equation is SNR = P/NEP. A smaller NEP corresponds to a more sensitive detector. For exa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Robert Clark Jones
R. Clark Jones (June 30, 1916April 26, 2004) was an American physicist working in the field of optics. He studied at Harvard University and received his PhD in 1941. He worked at Bell Labs until 1944, and later with the Polaroid Corporation until 1982. In a sequence of publications between 1941 and 1956, he demonstrated a mathematical model to describe the polarization of coherent light, the Jones calculus. When William Shurcliff wrote ''Polarized Light: Production and Use'' he praised R. C. Jones in the preface: "The author’s debt to Dr. R. Clark Jones, the inventor of the Jones calculus, is immeasurable. The sections dealing with the Stokes vector, the Mueller calculus, and the Jones calculus could not have been written without long and painstaking coaching by him." William Shurcliff (1962) ''Polarized Light: Production and Use'', Harvard University Press Publications * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Responsivity
Responsivity is a measure of the input–output Gain (electronics), gain of a detector system. In the specific case of a photodetector, it measures the electrical output per optical input. A photodetector's responsivity is usually expressed in units of amperes or volts per watt of incident radiant flux, radiant power. For a system that responds linearly to its input, there is a unique responsivity. For nonlinear systems, the responsivity is the Derivative, local slope. Many common photodetectors respond linearly as a function of the incident power. Responsivity is a function of the wavelength of the incident Electromagnetic radiation, radiation and of the sensor's properties, such as the bandgap of the material of which the photodetector is made. One simple expression for the responsivity ''R'' of a photodetector in which an optical signal is converted into an electric current (known as a photocurrent) is : R=\eta\frac\approx\eta\frac where \eta is the quantum efficiency (the c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Noise Spectral Density
In communications, noise spectral density (NSD), noise power density, noise power spectral density, or simply noise density (''N''0) is the power spectral density of noise or the noise power per unit of bandwidth. It has dimension of power over frequency, whose SI unit is watt per hertz (W/Hz), equivalent to watt-second (Ws) or joule (J). It is commonly used in link budgets as the denominator of the important figure-of-merit ratios, such as carrier-to-noise-density ratio as well as ''E''''b''/''N''0 and ''E''''s''/''N''0. If the noise is one-sided white noise, i.e., constant with frequency, then the total noise power ''N'' integrated over a bandwidth ''B'' is ''N'' = ''BN''0 (for double-sided white noise, the bandwidth is doubled, so ''N'' is ''BN''0/2). This is utilized in signal-to-noise ratio calculations. For thermal noise, its spectral density is given by ''N''0 = ''kT'', where ''k'' is the Boltzmann constant in joules per kelvin (J/K), and ''T'' is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Root Mean Square
In mathematics, the root mean square (abbrev. RMS, or rms) of a set of values is the square root of the set's mean square. Given a set x_i, its RMS is denoted as either x_\mathrm or \mathrm_x. The RMS is also known as the quadratic mean (denoted M_2), a special case of the generalized mean. The RMS of a continuous function is denoted f_\mathrm and can be defined in terms of an integral of the square of the function. In estimation theory, the root-mean-square deviation of an estimator measures how far the estimator strays from the data. Definition The RMS value of a set of values (or a continuous-time waveform) is the square root of the arithmetic mean of the squares of the values, or the square of the function that defines the continuous waveform. In the case of a set of ''n'' values \, the RMS is : x_\text = \sqrt. The corresponding formula for a continuous function (or waveform) ''f''(''t'') defined over the interval T_1 \le t \le T_2 is : f_\text = \sqrt , and the R ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Solid Angle
In geometry, a solid angle (symbol: ) is a measure of the amount of the field of view from some particular point that a given object covers. That is, it is a measure of how large the object appears to an observer looking from that point. The point from which the object is viewed is called the ''apex'' of the solid angle, and the object is said to '' subtend'' its solid angle at that point. In the International System of Units (SI), a solid angle is expressed in a dimensionless unit called a ''steradian'' (symbol: sr), which is equal to one square radian, sr = rad2. One steradian corresponds to one unit of area (of any shape) on the unit sphere surrounding the apex, so an object that blocks all rays from the apex would cover a number of steradians equal to the total surface area of the unit sphere, 4\pi. Solid angles can also be measured in squares of angular measures such as degrees, minutes, and seconds. A small object nearby may subtend the same solid angle as a larger object ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Etendue
Etendue or étendue (; ) is a property of light in an optical system, which characterizes how "spread out" the light is in area and angle. It corresponds to the beam parameter product (BPP) in Gaussian beam optics. Other names for etendue include acceptance, throughput, light grasp, light-gathering power, optical extent, and the AΩ product. ''Throughput'' and ''AΩ product'' are especially used in radiometry and radiative transfer where it is related to the view factor (or shape factor). It is a central concept in nonimaging optics. From the source point of view, etendue is the product of the area of the source and the solid angle that the system's entrance pupil subtends as seen from the source. Equivalently, from the system point of view, the etendue equals the area of the entrance pupil times the solid angle the source subtends as seen from the pupil. These definitions must be applied for infinitesimally small "elements" of area and solid angle, which must then b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Black-body Radiation
Black-body radiation is the thermal radiation, thermal electromagnetic radiation within, or surrounding, a body in thermodynamic equilibrium with its environment, emitted by a black body (an idealized opaque, non-reflective body). It has a specific continuous spectrum that depends only on the body's temperature., Chapter 13. A perfectly-insulated enclosure which is in thermal equilibrium internally contains blackbody radiation and will emit it through a hole made in its wall, provided the hole is small enough to have a negligible effect upon the equilibrium. The thermal radiation spontaneously emitted by many ordinary objects can be approximated as blackbody radiation. Of particular importance, although planets and stars (including the Earth and Sun) are neither in thermal equilibrium with their surroundings nor perfect black bodies, blackbody radiation is still a good first approximation for the energy they emit. The term ''black body'' was introduced by Gustav Kirchhoff in 1860. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Sensitivity (electronics)
The sensitivity of an electronic device, such as a communications system receiver, or detection device, such as a PIN diode, is the minimum magnitude of input signal required to produce a specified output signal having a specified signal-to-noise ratio, or other specified criteria. In general, it is the signal level required for a particular quality of received information. In signal processing, sensitivity also relates to bandwidth and noise floor as is explained in more detail below. In the field of electronics different definitions are used for sensitivity. The IEEE dictionary states: "Definitions of sensitivity fall into two contrasting categories." It also provides multiple definitions relevant to sensors among which 1: "(measuring devices) The ratio of the magnitude of its response to the magnitude of the quantity measured.” and 2: "(radio receiver or similar device) Taken as the minimum input signal required to produce a specified output signal having a specified sign ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Physical Quantities
A physical quantity (or simply quantity) is a property of a material or system that can be quantified by measurement. A physical quantity can be expressed as a ''value'', which is the algebraic multiplication of a '' numerical value'' and a ''unit of measurement''. For example, the physical quantity mass, symbol ''m'', can be quantified as ''m'n''kg, where ''n'' is the numerical value and kg is the unit symbol (for kilogram). Quantities that are vectors have, besides numerical value and unit, direction or orientation in space. Components Following ISO 80000-1, any value or magnitude of a physical quantity is expressed as a comparison to a unit of that quantity. The ''value'' of a physical quantity ''Z'' is expressed as the product of a ''numerical value'' (a pure number) and a unit 'Z'' :Z = \ \times /math> For example, let Z be "2 metres"; then, \ = 2 is the numerical value and = \mathrm is the unit. Conversely, the numerical value expressed in an arbitrary unit can ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |