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Photonics Dictionary: H

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henry; hecto-; hour; Planck constant
H-plane bend
With respect to waveguides, the continuous change in the direction of the axis of the wavelength, during which the axis is perpendicular to the direction of polarization.
A defect in the cleaved end face of an optical fiber, defined as multiple surface irregularities across the fiber surface. A less serious imperfection of the same nature is known as mist.
heat-assisted detection and ranging
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...
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...
half bandwidth
The term half bandwidth (HBW) generally refers to the width of a spectral band or frequency range at half of its maximum amplitude. It is commonly used in the context of signal processing, optics,...
half duplex
A communications system that can transmit in only a single direction at a time. See duplex.
half silvered
Describing a surface that is coated with a film of metal of such thickness that it transmits about one-half of the incident light and reflects about one-half.
half wave
Refers to half a wave cycle.
half-power point
1. The value on either the leading or the trailing edge of a laser pulse at which the power is one-half of its maximum value. 2. The wavelength at which a filter is transmitting one-half of its peak...
half-shade device
A device for forming at least two adjacent areas of polarized light. The angle between the directions of vibration of the light waves in the two areas is generally small.
half-shade plate
A semicircular, half-wave quartz plate between the polarizer and analyzer. It often is used in forming precision settings with a polariscope.
half-wave plate
A plate of electro-optical material that serves to rotate the plane of polarization of a light beam.
half-wave voltage
That voltage required across a Pockels, Kerr or other electro-optic light modulator to retard one polarization electrical vector by one-half a wavelength relative to the other. It corresponds to a...
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.
The gray-colored tones halfway between shadows and highlights in a reproduced image.
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...
Hall effect
The development of a transverse electric field in a solid material when it carries an electric current and is placed in a magnetic field that is perpendicular to the current.
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...
high-altitude large optics
Any of the five elements astatine, chlorine, fluorine, bromine and iodine, grouped because their chemical properties are similar.
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...
highly accelerated life test
halving line
The line that divides the two half-images in a coincidence rangefinder. The two halves of the images formed by the two objectives of the instrument must be brought to a point where they coincide...
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 coating
Usually a dielectric coating on glass or plastic optics; a coating that is comparable in hardness to glass itself.
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 seal
The process of sealing laser components by means of frit seals, welding or bonding rather than using epoxy.
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.
hard x-ray
A type of x-ray that is capable of deep penetration; its wavelength is about 10-8 cm.
hard-clad silica fiber
A type of optical fiber in which a silica core is surrounded by a hard polymer or similar material much stronger than the customary cladding material.
In the most general sense, the resistance of a solid surface to damage.
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....
harmonic wave analyzer
An instrument designed to calculate the amplitude and phase of the different harmonic elements of a radiation wave utilizing a graph of the wave.
Harting Dove prism
A direct-vision prism made in one piece that can be used only in parallel light.
Hartmann formula -> dispersion formula
All formulas that present the index of refraction as a function of a wavelength of electromagnetic radiation. Also called dispersion equation, Cauchy formula, Hartmann formula.
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....
highly accelerated stress screen
heat-affected zone
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 factor
The ratio between the luminescence of an object and the luminescence of the scattering medium through which it is being viewed.
haze filter
A filter, used in photography, that absorbs the ultraviolet and extreme blue violet radiation scattered by atmospheric haze.
high-brightness LED
holographic beam sampler
half bandwidth
high-performance CCD
high-index-contrast subwavelength grating

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