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Photonics Dictionary: H

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HCMM
heat capacity mapping mission
HCN
hydrogen cyanide
HCS
hard-clad silica
HD
half duplex
HDA
head-disc assembly
HDSL
high-bit-rate digital subscriber loop
HDTV
high-definition TV
HDVS
high-definition video systems
HDWDM
high-density wavelength division multiplex
HE11 mode
Designation for the fundamental mode of an optical fiber.
HEA
high-efficiency antireflection
head-up display
An optical system that superimposes a synthetic display providing navigational or weapon-aiming information on a pilot's or driver's field of view. The system includes a cathode-ray tube, collimating...
HEAO
high-energy astronomy observatory
heat equation
A calorimetric calculation from which the temperature vs. time dependence of any point on a sample can be determined, provided surface and bulk absorption, thermal conductivity and heat transfer...
heat exchanger
A type of cooling system in which one fluid is used to carry heat off another without direct contact between the two.
heat filter -> heat-transmitting filter
A filter that allows heat radiation from an incident beam to pass without absorption or reflection.
heat lamp
A lamp designed to emit a large amount of infrared radiation; used in applications requiring heat.
heat sink
A series of flanges or other conducting surfaces, usually metal, attached to an electronic device to transmit and dissipate heat that might damage internal circuitry.
heat treating
The process of subjecting glass to temperature cycling to produce physico-chemical reactions that alter its properties. Similar processes can be accomplished with a laser -- most commonly a CO2,...
heat wave
In reference to infrared, emissions that are like radio waves but that have a higher frequency.
heat-absorbing filter
A glass filter that transmits visible light while absorbing infrared energy (heat).
heat-resistant glass
Glass that has been specially treated so that it will not shatter when exposed to high temperatures followed by immediate and rapid cooling.
heat-transmitting filter
A filter that allows heat radiation from an incident beam to pass without absorption or reflection.
heatseeker
A guided missile that uses an infrared sensor to detect and home in on an enemy target. The missile is guided by the high infrared emissions produced by a target, such as the heat from an aircraft or...
heavy seeds
A condition in which the solid inclusions within a glass blank are very numerous, such as 25 or more to the square inch.
HEBS
high energy beam sensitive
hecto
In the SI system, prefix meaning one hundred, 102.
Hefner unit lamp
A gas lamp used in the early 1900s as a physical standard for measurement of luminous intensity. The Hefner unit was superseded by the candle and then by the candela.
height-range indicator
A display that allows the observation and measurement of the altitude and range of airborne objects.
heightfinder
A rangefinder used to determine the height or altitude of aerial targets by means of optical triangulation. The device employs the stereoscopic principle.
HEL
high-energy laser
helical scanning
A method used in facsimile scanning that sweeps the elemental area across the copy in a spiral motion as the result of the movement of a single turn helix against a stationary bar.
heliograph
An instrument designed to record the duration and intensity of solar radiation.
heliostat
A device having a plane mirror so mounted that it can be set to reflect sunlight into a piece of laboratory equipment. It is driven by a clock to compensate for the sun's daily motion around the pole...
helium leak detector
A small mass spectrometer used to find leaks in a vacuum system by detecting the presence of helium. Using a magnetic deflection device that is permanently tuned to helium, it is capable of detecting...
helium-neon laser
A helium-neon (HeNe) laser is a type of gas laser that emits visible red light at a wavelength of 632.8 nm. It operates based on the principle of stimulated emission of photons from excited helium...
helmet-mounted display
A compact optical projection system, mounted on or built into a helmet, and used to project data or a scene directly into the eyes of the wearer. Also called visually coupled display.
Helmholtz reciprocal relationship
The capability of the spatial distributions of incident and reflected flux to interchange completely without alteration of the measured reflectance.
HEM
hybrid electromagnetic wave; heat exchange method
hematofluorometer
A photoanalytical instrument for analysis of jaundice conditions in infants that measures bilirubin (a breakdown product of hemoglobin that produces jaundice), albumen-carrying capacity and binding...
hematoporphyrin derivative
A material used in photodynamic therapy that is retained selectively by tumor tissue when injected into the body; it then fluoresces when exposed to blue light and necroses when exposed to red laser...
hemispherical cavity
Laser cavity bounded by a plane mirror and a concave spherical mirror with the plane mirror located at the center of curvature of the concave mirror.
HEMT
high-electron-mobility transistor
henry
The inductance of a closed circuit in which an electromotive force of one volt is produced when the electric current in the circuit is varied uniformly at a rate of one ampere per second.
HEPA
high-efficiency particulate air
hermetic bonding
The total fusion and sealing of materials, or usually an enclosure, to ensure that they are airtight.
hero experiments
Laboratory experiments that focus on demonstrating new capabilities of a certain technology or device, usually without consideration of industrial or commercial practicality.
Herschel effect
The decrease in effect in developable density on a photographic plate formed by a second exposure to radiation having a longer wavelength, usually red or infrared.
Hertz effect
The ionization and spark emission due to exposure to ultraviolet radiation.
hertz
A unit of frequency equivalent to one cycle per second.

Photonics DictionaryH

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