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Photonics Dictionary: H

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horizontal temperature gradients
Horizontal concentrations that comprise the dominant factor in atmospheric gradient correction. The range bias near due north and due south azimuths coincides with the systematic decrease in surface...
horizontal travel
The rotation of an instrument (or the line of sight of an optical system) in a horizontal plane; transverse.
horopter
The locus of the points in the field of binocular vision that are observed singly. The images of these points correspond to the respective retinal points.
hot extrusion
A method of manufacturing polycrystalline infrared-transmitting optical fiber by heating a single halide crystal billet and forcing it through a die.
hot mirror
A mirror with a coating that reflects infrared radiation and transmits visible light.
hot shoe -> accessory shoe
Mount attached to a camera or camcorder which allows the user to attach a microphone or flash unit.
hot spot
Term applied to laser technology to denote an area of above-average intensity often attributable to atmospheric inconsistencies.
HP
high pass
HPA
high-power amplifier
HPD
hematoporphyrin derivative
HPF
high-pass filter
HPFL
high-power fiber laser
HPLC
high-performance liquid chromatography
HPP
half-power point
HPV
holographic particle velocimetry
HR
high resolution
HRI
high-resolution imaging
HRIR
high-resolution infrared radiometer
HRPT
high-resolution picture transmission
HRV
high-resolution visible
HSI
hyperspectral imaging
HSU
holographic scanning unit
HTL
high-threshold logic
HTS
high-throughput screening
hub
The center of a local area network in the star topology.
Hubble effect -> redshift
The displacement of spectrum lines, as determined by the increasing distance between, and the relative velocity of, the observer and a light source, causing the lines to move toward the red portion...
Hubner rhomb
A glass rhomb that is used in photometry to compare two illuminated surfaces. This is accomplished by the rhomb's angles, which transmit two light beams, one from each of the two surfaces, so that...
HUD
head-up display
hue
The perceptual term for that aspect of color described by words such as red, yellow or blue. Achromatic colors, such as white, gray and black, do not exhibit hue.
Huefner spectrophotometer
A visual spectrophotometer with a rhomb located directly before the entrance aperture of a constant-deviation spectrophotometer.
Hurter-Driffield curve
A plotted relation between Log E (logarithm to base 10 of exposure in metercandle seconds) and density (logarithm to base 10 of opacity).
Huygenian eyepiece
An ocular having two planoconvex lenses that are formed from similar glass and that are separated by a space equal to half the sum of their focal lengths. This eyepiece is free of lateral chromatic...
Huygens principle
An analysis used for problems of wave propagation. The principle notes that each point of an advancing wavefront is the center of a new disturbance, the source of a new series of waves. It also notes...
HVEM
high-voltage electron microscope
HVL
half-value layer
HWFM
half wave full maximum
hybrid cable
A cable assembly containing both optical fibers and copper electrical conductors in the same jacket.
hybrid circuit
Any integrated circuit that also makes use of one or more discrete components; frequently used to describe circuits that combine both photonic and electronic components.
hybrid cooler
A cryogenic cooler device that is an intermittent Joule-Thomson refrigerator with a passive radiator serving as the precooler. Used for satellite applications, the device has Joule-Thomson and gas...
hybrid electromagnetic wave
A wave in the electromagnetic spectrum that has both electrical and magnetic field vectors in the direction of propagation.
hybrid focal plane array
A device where each pixel in the detector array is mated with a preamplifier on a single silicon chip, providing sensing and signal processing capabilities.
hybrid image recording device
A single housing that includes means of recording an image photographically and electronically.
hybrid mode
A mode possessing components of both electrical and magnetic field vectors in the direction of propagation.
hybrid mosaic on stacked silicon
A sensor module used in advanced pattern recognition systems, containing signal-processing integrated circuits stacked and connected by a busing circuit.
hybrid optical integrated circuit
Device in which the various circuit elements are fabricated in different substrate materials and then appropriately joined together so that the various substrate materials can be chosen to optimize...
hydrogel
A hydrogel is a three-dimensional network of polymer chains that are hydrophilic, meaning they have a strong affinity for water. This network structure allows hydrogels to absorb and retain large...
hydrogen cyanide laser
A gas laser having a mixture of gases that makes it useful in the lab. The mixture of gases flows through a pressure and gas-flow-rate-regulated, sealed vessel with such a gain that only the...
hydrogenated amorphous silicon
A photoreceptor material used in solar cells and in drums for laser printers and high-speed copiers because of its high quantum efficiency over a wide spectral band, high data-rate capability and...
hydrophilic
Hydrophilic is a term used to describe substances or materials that have an affinity for water. The word hydrophilic comes from the Greek words "hydro," meaning water, and "philos," meaning loving or...
hydrophobic
Hydrophobic is a term used to describe substances or materials that repel or do not readily interact with water. The word hydrophobic comes from the Greek words "hydro," meaning water, and "phobos,"...

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