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131 terms
Photonics Dictionary: H
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h
henry; hecto-; hour; Planck constant
Haidinger fringes
Also known as constant angle or constant deviation fringes. The interference fringes observed with dense flat plates near normal incidence. The fringes of the Fabry-Perot interferometer are Haidinger...
hair-trigger operation
Triggering a laser at a predetermined time by pumping it to a level just below its threshold and then using an auxiliary source that quickly pumps it above threshold. Means of achieving it in laser...
halation
1. In a cathode-ray tube, the glow surrounding a bright spot that appears on the fluorescent screen as the result of the screen's light being reflected by the front and rear surfaces of the tube's...
halftone screen
A plate containing a uniform pattern of transparent holes in an opaque background, the clear area being nearly equal to the opaque area. Used in the printing process.
halide
In chemistry, a halide refers to a chemical compound containing one or more halogen atoms bonded to another element. The halogens are a group of elements in the periodic table that includes fluorine...
halo
1. The faintly hued ring that is seen to surround a light source viewed through fog or light clouds. The size of scattering particles determines the size of the ring. 2. The ring surrounding a...
halogen lamp
A halogen lamp, also known as a tungsten halogen, quartz-halogen, or quartz iodine lamp, is an incandescent lamp that uses a tungsten filament surrounded by a small amount of halogen gas, such as...
hand viewer
A device small enough to be held in a hand that uses a magnifying lens and a translucent back to permit the viewing of photographic transparencies.
hard copy
Text or images printed on paper or another tangible medium, as opposed to those viewed electronically on a cathode-ray-tube screen.
hard elastics
High-modulus elastic fibers that exhibit the following differences from conventional elastic fibers: Increasing temperature decreases recovery force (the fibers are enthalpic vs. conventionally...
hard tube
->
high-vacuum tube
An electron tube whose electrical characteristics will not be affected by gaseous ionization because of its high degree of evacuation. Also known as a hard tube.
harmonic generation
Harmonic generation refers to a nonlinear optical process in which incoming photons interact with a material and produce new photons at integer multiples of the frequency of the incoming photons....
Hartmann test
A test for spherical aberration, coma or astigmatism in which incident rays from a point source are isolated by small holes in a metal disc located close to the lens or mirror under test....
haze
An aggravated form of fog in a polished surface caused by the scattering of light. The defects causing haze are larger than those causing fog, but singly are not large enough to be seen by the...
haze filter
A filter, used in photography, that absorbs the ultraviolet and extreme blue violet radiation scattered by atmospheric haze.
HBS
holographic beam sampler
head-up display
A head-up display (HUD) is a transparent display technology that presents information directly in the field of view of a user, typically without requiring the user to look away from their usual...
heat affected zone
The heat-affected zone (HAZ) refers to the portion of a material, typically metal, that experiences changes in its microstructure and mechanical properties due to the heat generated during welding,...
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 sink
A heat sink for a laser is a device designed to absorb and dissipate the excess heat generated by the laser during operation. This is crucial to maintain the laser's performance, prevent overheating,...
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...
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.
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...
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...
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.
heterochromatic photometry
Light measurement by comparison of the luminances of unlike chromaticities.
heterodyne
The interaction between two oscillations of unlike frequencies that forms other oscillations, specifically those with a frequency equal to the frequency difference of the former oscillations.
heterodyne receiver
A type of receiver that uses a local oscillator at a frequency deliberately offset from that of the incoming signal. It is less sensitive than a homodyne receiver, but easier to build because it...
heterogeneous
Property of a substance whose volume elements differ in composition and optical properties.
heterojunction
A heterojunction is a junction formed between two different semiconductor materials with differing band gaps. These materials can be of the same or different types (e.g., both n-type, both p-type, or...
heterostructures
A method used in integrated optics; formed by growing an epitaxial layer of active material, removing it from its base and splicing it onto a passive substrate.
Higgs boson
The Higgs boson is a fundamental particle associated with the Higgs field, a field that permeates the universe and is responsible for giving mass to other fundamental particles through the mechanism...
high contrast
A term used to describe a photograph, film or television picture where the values for black and white areas are at or near their limits, thereby giving the maximum degree of difference between them.
high harmonic generation
High harmonic generation (HHG) refers to a nonlinear optical process in which intense laser light interacts with a gaseous medium, typically an atom or a molecule, to produce harmonics of the...
high-content screening
Also known as HCS, an analytical method designed to collect statistically relevant amounts of quantitative data on many parallel cell populations or processes within cells through the combination of...
high-density storage
Extensive data storage in the form of bits, with the use of high-resolution photographic materials and optics, and generally a laser.
high-sensitivity camera
A high-sensitivity camera is a type of camera designed to perform well in low light conditions, capturing clear and detailed images with minimal noise. These cameras typically feature advanced sensor...
high-speed holography
The holographic recording of sequences of high-speed phenomena. With a multiple beam laser, multiple holograms that depict rapid events can be formed on a single medium.
high-speed motion camera
A high-speed motion camera, also known as a high-speed camera or slow-motion camera, is a specialized imaging device designed to capture fast-moving events or phenomena at extremely high frame rates....
high-speed movie camera
A camera designed to record at rates exceeding 50 fps. For frame rates up to about 500 fps, an ordinary pull-down mechanism can be used. From 500 to 1000 fps, the film must be moved continuously, the...
high-speed photography
Photography involving the recording of events that occur too fast to be perceived by the human eye or recorded by conventional photographic techniques. See high-speed movie camera; high-speed...
high-speed radiography
A method of producing x-ray exposures as short as 0.03 µs; the primary application is in ballistic radiography.
high-speed shutter
A shutter actuated by means other than mechanical springs for timings on the order of nanoseconds. The shutter is used in the photography of rapid moving objects or events.
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Photonics Dictionary
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