Absorptive Filter
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A filter that absorbes some wavelengths of incident radiation whilst transmitting others.
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Acoustic Absorption
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The process by which a material, structure, or object takes in sound energy when sound waves are encountered, as opposed to reflecting the energy. Part of the absorbed energy is transformed into heat and part is transmitted through the absorbing body.
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Acoustics
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The the use of structures or other systems to affect the generation, propagation and reception of mechanical waves and vibrations.
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Anechoic Chamber
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A room designed to stop reflections of either sound or electromagnetic waves. They are also insulated from exterior sources of noise. Used to simulate a quiet open-space of infinite dimension. Originally used in the context of acoustics (sound waves), their radiofrequency counterpart is also used, for example to test antennas, radars, or electromagnetic interference.
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Bragg Diffraction
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Diffraction from a three dimensional periodic structure such as atoms in a crystal. It is similar to what occurs when waves are scattered from a diffraction grating. Bragg diffraction is a consequence of interference between waves reflecting from different crystal planes.
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Dichroic Filter
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A colour filter based on the use of the principle of interference, typically used to selectively pass light of a small range of colours while reflecting other colours
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Dielectric Permittivity
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The measure of how much resistance is encountered when forming an electric field in a medium. In other words, permittivity is a measure of how an electric field affects, and is affected by, a dielectric medium. Permittivity is determined by the ability of a material to polarize in response to the field, and thereby reduce the total electric field inside the material. Thus, permittivity relates to a material's ability to transmit (or 'permit') an electric field.
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In the case of an electric field.
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Diffraction
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Various phenomena which occur when a wave encounters an obstacle. It is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings. Very similar effects are observed when there is an alteration in the properties of the medium in which the wave is travelling, for example a variation in refractive index for light waves or in acoustic impedance for sound waves and these can also be referred to as diffraction effects.
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Diffraction Grating
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An optical component with a regular pattern, which splits (diffracts) light into several beams travelling in different directions. The directions of these beams depend on the spacing of the grating and the wavelength of the light so that the grating acts as a dispersive element. Because of this, gratings are commonly used in monochromators and spectrometers.
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Diode
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A device that allows an electric current to pass in one direction (called the forward biased condition) and blocks the current in the opposite direction (the reverse biased condition). Real diodes do not display such a perfect on-off directionality but have a more complex non-linear electrical characteristic, which depends on the particular type of diode technology. Diodes also have many other functions in which they are not designed to operate in this on-off manner.
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Earthing
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The connection of an electrical conductor to ground or earth. Used to provide a reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth.
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Electro-Optic Effects
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A change in the optical properties of a material in response to an electric field that varies slowly compared with the frequency of light. The term encompasses a number of distinct phenomena, which can be subdivided into a) change of the absorption (electroabsorption, Franz-Keldysh effect, Quantum-confined Stark effect, electro-chromatic effect) and b) change of the refractive index(Pockels effect, Kerr Effect, electro-gyration)
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Filter (electronic)
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Electronic circuits which perform signal processing functions, specifically intended to remove unwanted signal components and/or enhance wanted ones.
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Filter (optical)
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Optical filters selectively transmits light having certain properties (often, a particular range of wavelengths, that is, range of colours of light), while blocking the remainder. Optical filters, generally, belong to one of two categories. The simplest, physically, is the absorptive filter, while the latter category, that of interference or dichroic filters, can be quite complex.
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Interference
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The addition (superposition) of two or more waves that result in a new wave pattern. As most commonly used, the term interference usually refers to the interaction of waves which are correlated or coherent with each other, either because they come from the same source or because they have the same or nearly the same frequency.
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By destructive interference. For example: noise cancelling headphones.
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Photonic Crystal
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Periodic optical (nano)structures that affect the propagation of electromagnetic waves, useful for controlling and manipulating the flow of light.
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Plenoptic Camera
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(also called a light-field camera) A camera that uses a microlens array to capture 4D light field information about a scene. Such light field information can be used to improve the solution of computer graphics and vision-related problems.
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Polarisation
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A 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 polarisation), or the oscillation direction may rotate as the wave travels (circular or elliptical polarisation).
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Shadow
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An area where direct light (or other radiation) from a source cannot reach due to obstruction by an object. The cross section of a shadow is a two-dimensional silhouette, or reverse projection of the object blocking the light (or radiation).
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Super Black
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A surface treatment (based upon chemically etching a nickel-phosphorus alloy) that reflects much less light than the darkest conventional matte black paints.Conventional black paint reflects about 2.5% of the incident light. Super black absorbs approximately 99.6% of light at normal incidence. At other angles of incidence, super black is even more effective.
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