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Organic Photorefractive Materials
Organic photorefractive materials are materials that exhibit a temporary change in refractive index when exposed to light. The changing refractive index causes light to change speed throughout the material and produce light and dark regions in the crystal. The buildup can be controlled to produce holographic images for use in biomedical scans and optical computing. The ease with which the chemical composition can be changed in organic materials makes the photorefractive effect more controllable. History Although the physics behind the photorefractive effect were known for quite a while, the effect was first observed in 1967 in LiNbO3. For more than thirty years, the effect was observed and studied exclusively in inorganic materials, until 1990, when a nonlinear organic crystal 2-(cyclooctylamino)-5-nitropyridine (COANP) doped with 7,7,8,8-tetracyanoquinodimethane (TCNQ) exhibited the photorefractive effect. Even though inorganic material-based electronics dominate the current mark ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Refractive Index
In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or refracted, when entering a material. This is described by Snell's law of refraction, , where ''θ''1 and ''θ''2 are the angle of incidence and angle of refraction, respectively, of a ray crossing the interface between two media with refractive indices ''n''1 and ''n''2. The refractive indices also determine the amount of light that is reflected when reaching the interface, as well as the critical angle for total internal reflection, their intensity ( Fresnel's equations) and Brewster's angle. The refractive index can be seen as the factor by which the speed and the wavelength of the radiation are reduced with respect to their vacuum values: the speed of light in a medium is , and similarly the wavelength in that medium is , where ''Π... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Doping (semiconductor)
In semiconductor production, doping is the intentional introduction of impurities into an intrinsic semiconductor for the purpose of modulating its electrical, optical and structural properties. The doped material is referred to as an extrinsic semiconductor. Small numbers of dopant atoms can change the ability of a semiconductor to conduct electricity. When on the order of one dopant atom is added per 100 million atoms, the doping is said to be ''low'' or ''light''. When many more dopant atoms are added, on the order of one per ten thousand atoms, the doping is referred to as ''high'' or ''heavy''. This is often shown as ''n+'' for n-type doping or ''p+'' for p-type doping. (''See the article on semiconductors for a more detailed description of the doping mechanism.'') A semiconductor doped to such high levels that it acts more like a conductor than a semiconductor is referred to as a degenerate semiconductor. A semiconductor can be considered i-type semiconductor if it has ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Centrosymmetry
In crystallography, a centrosymmetric point group contains an inversion center as one of its symmetry elements. In such a point group, for every point (x, y, z) in the unit cell there is an indistinguishable point (-x, -y, -z). Such point groups are also said to have ''inversion'' symmetry. Point reflection is a similar term used in geometry. Crystals with an inversion center cannot display certain properties, such as the piezoelectric effect. The following space groups have inversion symmetry: the triclinic space group 2, the monoclinic 10-15, the orthorhombic 47-74, the tetragonal 83-88 and 123-142, the trigonal 147, 148 and 162-167, the hexagonal 175, 176 and 191-194, the cubic 200-206 and 221-230. Point groups lacking an inversion center (non-centrosymmetric) can be ''polar'', ''chiral'', both, or neither. A ''polar'' point group is one whose symmetry operations leave more than one common point unmoved. A polar point group has no unique origin because each of those un ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phase Velocity
The phase velocity of a wave is the rate at which the wave propagates in any medium. This is the velocity at which the phase of any one frequency component of the wave travels. For such a component, any given phase of the wave (for example, the crest) will appear to travel at the phase velocity. The phase velocity is given in terms of the wavelength (lambda) and time period as :v_\mathrm = \frac. Equivalently, in terms of the wave's angular frequency , which specifies angular change per unit of time, and wavenumber (or angular wave number) , which represent the angular change per unit of space, :v_\mathrm = \frac. To gain some basic intuition for this equation, we consider a propagating (cosine) wave . We want to see how fast a particular phase of the wave travels. For example, we can choose , the phase of the first crest. This implies , and so . Formally, we let the phase and see immediately that and . So, it immediately follows that : \frac = -\frac \frac = \frac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electro-optic Effect
Electro–optics is a branch of electrical engineering, electronic engineering, materials science, and material physics involving components, electronic devices such as lasers, laser diodes, LEDs, waveguides, etc. which operate by the propagation and interaction of light with various tailored materials. It is closely related to the branch of optics, involving application of generation of photons, called photonics. It is not only concerned with the "electro–optic effect", since it deals with the interaction between the electromagnetic (optical) and the electrical (electronic) states of materials. Electro-optical devices The electro-optic effect is a change in the optical properties of an optically active material due to interaction with light. This interaction usually results in a change in the birefringence, and not simply the refractive index of the medium. In a Kerr cell, the change in birefringence is proportional to the square of the optical electric field, and the mat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Attenuation Coefficient
The linear attenuation coefficient, attenuation coefficient, or narrow-beam attenuation coefficient characterizes how easily a volume of material can be penetrated by a beam of light, sound, particles, or other energy or matter. A coefficient value that is large represents a beam becoming 'attenuated' as it passes through a given medium, while a small value represents that the medium had little effect on loss. The SI unit of attenuation coefficient is the reciprocal metre (m−1). Extinction coefficient is another term for this quantity, often used in meteorology and climatology. Most commonly, the quantity measures the exponential decay of intensity, that is, the value of downward ''e''-folding distance of the original intensity as the energy of the intensity passes through a unit (''e.g.'' one meter) thickness of material, so that an attenuation coefficient of 1 m−1 means that after passing through 1 metre, the radiation will be reduced by a factor of '' e'', and for material ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Irradiance
In radiometry, irradiance is the radiant flux ''received'' by a ''surface'' per unit area. The SI unit of irradiance is the watt per square metre (W⋅m−2). The CGS unit erg per square centimetre per second (erg⋅cm−2⋅s−1) is often used in astronomy. Irradiance is often called intensity, but this term is avoided in radiometry where such usage leads to confusion with radiant intensity. In astrophysics, irradiance is called ''radiant flux''. Spectral irradiance is the irradiance of a surface per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength. The two forms have different dimensions and units: spectral irradiance of a frequency spectrum is measured in watts per square metre per hertz (W⋅m−2⋅Hz−1), while spectral irradiance of a wavelength spectrum is measured in watts per square metre per metre (W⋅m−3), or more commonly watts per square metre per nanometre (W⋅m−2⋅nm−1). Mathematical ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Planck Constant
The Planck constant, or Planck's constant, is a fundamental physical constant of foundational importance in quantum mechanics. The constant gives the relationship between the energy of a photon and its frequency, and by the mass-energy equivalence, the relationship between mass and frequency. Specifically, a photon's energy is equal to its frequency multiplied by the Planck constant. The constant is generally denoted by h. The reduced Planck constant, or Dirac constant, equal to the constant divided by 2 \pi, is denoted by \hbar. In metrology it is used, together with other constants, to define the kilogram, the SI unit of mass. The SI units are defined in such a way that, when the Planck constant is expressed in SI units, it has the exact value The constant was first postulated by Max Planck in 1900 as part of a solution to the ultraviolet catastrophe. At the end of the 19th century, accurate measurements of the spectrum of black body radiation existed, but the distribut ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron Mobility
In solid-state physics, the electron mobility characterises how quickly an electron can move through a metal or semiconductor when pulled by an electric field. There is an analogous quantity for holes, called hole mobility. The term carrier mobility refers in general to both electron and hole mobility. Electron and hole mobility are special cases of electrical mobility of charged particles in a fluid under an applied electric field. When an electric field ''E'' is applied across a piece of material, the electrons respond by moving with an average velocity called the drift velocity, v_d. Then the electron mobility ''μ'' is defined as v_d = \mu E. Electron mobility is almost always specified in units of cm2/( V⋅ s). This is different from the SI unit of mobility, m2/( V⋅ s). They are related by 1 m2/(V⋅s) = 104 cm2/(V⋅s). Conductivity is proportional to the product of mobility and carrier concentration. For example, the same conductivity could come from a small numbe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrical Conductivity
Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows electric current. Resistivity is commonly represented by the Greek letter (rho). The SI unit of electrical resistivity is the ohm-meter (Ω⋅m). For example, if a solid cube of material has sheet contacts on two opposite faces, and the resistance between these contacts is , then the resistivity of the material is . Electrical conductivity or specific conductance is the reciprocal of electrical resistivity. It represents a material's ability to conduct electric current. It is commonly signified by the Greek letter ( sigma), but ( kappa) (especially in electrical engineering) and ( gamma) are sometimes used. The SI unit of electrical conductivity is siemens per metre (S/m). Resistivity and conductivity are inte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Doped Semiconductor II
Doping may refer to: * Doping, adding a dopant to something * Doping (semiconductor), intentionally introducing impurities into an extremely pure semiconductor to change its electrical properties * Aircraft dope, a lacquer that is applied to fabric-covered aircraft * Link doping, in search engine optimization Sports * Doping in sport, the use of drugs or other methods to improve athletic performance * Abortion doping, the rumoured practice of purposely inducing pregnancy for performance-enhancing benefits, then aborting * Blood doping, boosting the number of red blood cells in the bloodstream * Boosting (doping), a method of inducing autonomic dysreflexia * Gene doping, the hypothetical non-therapeutic use of gene therapy by athletes * Stem cell doping * Technology doping * Doping in China * Doping in Russia See also * Dope (other) Dope may refer to: Chemistry Biochemistry * Dope, a slang word for a euphoria-producing drug, particularly: ** Cocaine ** Cannabis (drug) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Charge Carriers
In physics, a charge carrier is a particle or quasiparticle that is free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors. Examples are electrons, ions and holes. The term is used most commonly in solid state physics. In a conducting medium, an electric field can exert force on these free particles, causing a net motion of the particles through the medium; this is what constitutes an electric current. In conducting media, particles serve to carry charge: *In many metals, the charge carriers are electrons. One or two of the valence electrons from each atom are able to move about freely within the crystal structure of the metal. The free electrons are referred to as conduction electrons, and the cloud of free electrons is called a Fermi gas. Many metals have electron and hole bands. In some, the majority carriers are holes. *In electrolytes, such as salt water, the charge carriers are ions, which are atoms or molecul ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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