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Optical Heterodyne Detection
Optical heterodyne detection is a method of extracting information encoded as modulation of the phase, frequency or both of electromagnetic radiation in the wavelength band of visible or infrared light. The light signal is compared with standard or reference light from a "local oscillator" (LO) that would have a fixed offset in frequency and phase from the signal if the latter carried null information. "Heterodyne" signifies more than one frequency, in contrast to the single frequency employed in homodyne detection. The comparison of the two light signals is typically accomplished by combining them in a photodiode detector, which has a response that is linear in energy, and hence quadratic in amplitude of electromagnetic field. Typically, the two light frequencies are similar enough that their difference or beat frequency produced by the detector is in the radio or microwave band that can be conveniently processed by electronic means. This technique became widely applicable t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Interferometry
Interferometry is a technique which uses the ''interference (wave propagation), interference'' of Superposition principle, superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, Optical fiber, fiber optics, engineering metrology, optical metrology, oceanography, seismology, spectroscopy (and its applications to chemistry), quantum mechanics, Nuclear physics, nuclear and particle physics, plasma physics, interactome, biomolecular interactions, surface profiling, microfluidics, mechanical stress/strain measurement, velocimetry, optometry, and making holograms. Interferometers are devices that extract information from interference. They are widely used in science and industry for the measurement of microscopic displacements, refractive index changes and surface irregularities. In the case with most interferometers, light from a single source is split into two beams that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Modulation
Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information. The process encodes information in form of the modulation or message signal onto a carrier signal to be transmitted. For example, the message signal might be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing a sequence of binary digits, a bitstream from a computer. This carrier wave usually has a much higher frequency than the message signal does. This is because it is impractical to transmit signals with low frequencies. Generally, receiving a radio wave requires a radio antenna with a length that is one-fourth of the wavelength of the transmitted wave. For low frequency radio waves, wavelength is on the scale of kilometers and building such a large antenna is not practical. Another purpose of modulation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
LIDAR
Lidar (, also LIDAR, an acronym of "light detection and ranging" or "laser imaging, detection, and ranging") is a method for determining ranging, ranges by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. Lidar may operate in a fixed direction (e.g., vertical) or it may scan multiple directions, in a special combination of 3-D scanning and laser scanning. Lidar has terrestrial, airborne, and mobile applications. It is commonly used to make high-resolution maps, with applications in surveying, geodesy, geomatics, archaeology, geography, geology, geomorphology, seismology, forestry, atmospheric physics, laser guidance, airborne laser swathe mapping (ALSM), and Mars Orbiter Laser Altimeter, laser altimetry. It is used to make digital 3D modeling, 3-D representations of areas on the Earth's surface and ocean bottom of the intertidal and near coastal zone by varying the wavelength of light. It has also been in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rainbow
A rainbow is an optical phenomenon caused by refraction, internal reflection and dispersion of light in water droplets resulting in a continuous spectrum of light appearing in the sky. The rainbow takes the form of a multicoloured circular arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the Sun. Rainbows can be caused by many forms of airborne water. These include not only rain, but also mist, spray, and airborne dew. Rainbows can be full circles. However, the observer normally sees only an arc formed by illuminated droplets above the ground, and centered on a line from the Sun to the observer's eye. In a primary rainbow, the arc shows red on the outer part and violet on the inner side. This rainbow is caused by light being refracted when entering a droplet of water, then reflected inside on the back of the droplet and refracted again when leaving it. In a double rainbow, a second arc is seen outside the primary arc, and has the or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Newton's Rings
Newton's rings is a phenomenon in which an interference pattern is created by the reflection of light between two surfaces, typically a spherical surface and an adjacent touching flat surface. It is named after Isaac Newton, who investigated the effect in 1666. When viewed with monochromatic light, Newton's rings appear as a series of concentric, alternating bright and dark rings centered at the point of contact between the two surfaces. When viewed with white light, it forms a concentric ring pattern of rainbow colors because the different wavelengths of light interfere at different thicknesses of the air layer between the surfaces. History The phenomenon was first described by Robert Hooke in his 1665 book ''Micrographia''. Its name derives from the mathematician and physicist Sir Isaac Newton, who studied the phenomenon in 1666 while sequestered at home in Lincolnshire in the time of the Great Plague that had shut down Trinity College, Cambridge. He recorded his observations ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical Coherence Tomography
Optical coherence tomography (OCT) is a high-resolution imaging technique with most of its applications in medicine and biology. OCT uses coherent near-infrared light to obtain micrometer-level depth resolved images of biological tissue or other scattering media. It uses interferometry techniques to detect the amplitude and time-of-flight of reflected light. OCT uses transverse sample scanning of the light beam to obtain two- and three-dimensional images. Short-coherence-length light can be obtained using a superluminescent diode (SLD) with a broad spectral bandwidth or a broadly tunable laser with narrow linewidth. The first demonstration of OCT imaging (in vitro) was published by a team from MIT and Harvard Medical School in a 1991 article in the journal ''Science (journal), Science''. The article introduced the term "OCT" to credit its derivation from optical coherence-domain reflectometry, in which the axial resolution is based on temporal coherence. The first demonstrat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
White Light Scanner
A white light scanner (WLS) is a device for performing surface height measurements of an object using coherence scanning interferometry ( CSI) with spectrally-broadband, "white light" illumination. Different configurations of scanning interferometer may be used to measure macroscopic objects with surface profiles measuring in the centimeter range, to microscopic objects with surface profiles measuring in the micrometer range. For large-scale non-interferometric measurement systems, see structured-light 3D scanner. Description Vertical scanning interferometry is an example of low-coherence interferometry, which exploits the low coherence of white light. Interference will only be achieved when the path length delays of the interferometer are matched within the coherence time of the light source. VSI monitors the fringe contrast rather than the shape of the fringes. Fig. 2 illustrates a Twyman–Green interferometer set up for white light scanning of a macroscopic object. L ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wideband
In communications, a system is wideband when the message bandwidth significantly exceeds the coherence bandwidth of the channel. Some communication links have such a high data rate that they are forced to use a wide bandwidth; other links may have relatively low data rates, but deliberately use a wider bandwidth than "necessary" for that data rate in order to gain other advantages; see '' spread spectrum''. A wideband antenna is one with approximately or exactly the same operating characteristics over a very wide Passband. It is distinguished from broadband antennas, where the passband is large, but the antenna gain and/or radiation pattern need not stay the same over the passband. The term Wideband Audio or (also termed HD Voice or Wideband Voice) denotes a telephony using a wideband codec, which uses a greater frequency range of the audio spectrum than conventional voiceband telephone calls, resulting in a clearer sound. Wideband in this context is usually consid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heterodyne Detection
A heterodyne is a signal frequency that is created by combining or mixing two other frequencies using a signal processing technique called ''heterodyning'', which was invented by Canadian inventor-engineer Reginald Fessenden. Heterodyning is used to shift signals from one frequency range into another, and is also involved in the processes of modulation and demodulation. The two input frequencies are combined in a nonlinear signal-processing device such as a vacuum tube, transistor, or diode, usually called a '' mixer''. In the most common application, two signals at frequencies and are mixed, creating two new signals, one at the sum of the two frequencies , and the other at the difference between the two frequencies . The new signal frequencies are called ''heterodynes''. Typically, only one of the heterodynes is required and the other signal is filtered out of the output of the mixer. Heterodyne frequencies are related to the phenomenon of " beats" in acoustics. A major a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electromagnetic Field
An electromagnetic field (also EM field) is a physical field, varying in space and time, that represents the electric and magnetic influences generated by and acting upon electric charges. The field at any point in space and time can be regarded as a combination of an electric field and a magnetic field. Because of the interrelationship between the fields, a disturbance in the electric field can create a disturbance in the magnetic field which in turn affects the electric field, leading to an oscillation that propagates through space, known as an ''electromagnetic wave''. The way in which charges and currents (i.e. streams of charges) interact with the electromagnetic field is described by Maxwell's equations and the Lorentz force law. Maxwell's equations detail how the electric field converges towards or diverges away from electric charges, how the magnetic field curls around electrical currents, and how changes in the electric and magnetic fields influence each other. The Lor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antenna (radio)
In radio-frequency engineering, an antenna (American English) or aerial (British English) is an electronic device that converts an alternating current, alternating electric current into radio waves (transmitting), or radio waves into an electric current (receiving). It is the interface between radio waves Radio propagation, propagating through space and electric currents moving in metal Electrical conductor, conductors, used with a transmitter or receiver (radio), receiver. In transmission (telecommunications), transmission, a radio transmitter supplies an electric current to the antenna's Terminal (electronics), terminals, and the antenna radiates the energy from the current as electromagnetic radiation, electromagnetic waves (radio waves). In receiver (radio), reception, an antenna intercepts some of the power of a radio wave in order to produce an electric current at its terminals, that is applied to a receiver to be amplifier, amplified. Antennas are essential components ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heterodyne
A heterodyne is a signal frequency that is created by combining or mixing two other frequencies using a signal processing technique called ''heterodyning'', which was invented by Canadian inventor-engineer Reginald Fessenden. Heterodyning is used to shift signals from one frequency range into another, and is also involved in the processes of modulation and demodulation. The two input frequencies are combined in a linear circuit, nonlinear signal-processing device such as a vacuum tube, transistor, or diode, usually called a ''frequency mixer, mixer''. In the most common application, two signals at frequencies and are mixed, creating two new signals, one at the sum of the two frequencies , and the other at the difference between the two frequencies . The new signal frequencies are called ''heterodynes''. Typically, only one of the heterodynes is required and the other signal is filter (signal processing), filtered out of the output of the mixer. Heterodyne frequencies are rela ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
