Photonics Dictionary: H

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.

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,...

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.

A display that allows the observation and measurement of the altitude and range of airborne objects.

A rangefinder used to determine the height or altitude of aerial targets by means of optical triangulation. The device employs the stereoscopic principle.

The total fusion and sealing of materials, or usually an enclosure, to ensure that they are airtight.

A superthin, highly reflective mirror.

A null optic in the form of a concave spherical mirror; used for the test and evaluation of a hyperboloidal aspheric surface.

The application of coherent wavefront techniques to the determination of the physical state of a system without appreciably altering that state.

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.

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...

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...

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.

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...

A semicircular, half-wave quartz plate between the polarizer and analyzer. It often is used in forming precision settings with a polariscope.

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...

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...

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...

Any of the five elements astatine, chlorine, fluorine, bromine and iodine, grouped because their chemical properties are similar.

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...

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...

High-modulus elastic fibers that exhibit the following differences from conventional elastic fibers: Increasing temperature decreases recovery force (the fibers are enthalpic vs. conventionally...

The process of sealing laser components by means of frit seals, welding or bonding rather than using epoxy.

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.

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....

An instrument designed to calculate the amplitude and phase of the different harmonic elements of a radiation wave utilizing a graph of the wave.

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....

The ratio between the luminescence of an object and the luminescence of the scattering medium through which it is being viewed.

A filter, used in photography, that absorbs the ultraviolet and extreme blue violet radiation scattered by atmospheric haze.

Designation for the fundamental mode of an optical fiber.

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...

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...

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.

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,...

Glass that has been specially treated so that it will not shatter when exposed to high temperatures followed by immediate and rapid cooling.

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...

A condition in which the solid inclusions within a glass blank are very numerous, such as 25 or more to the square inch.

In the SI system, prefix meaning one hundred, 102.

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.

An instrument designed to record the duration and intensity of solar radiation.

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...