Photonics Dictionary: H

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...

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.

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...

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 communications system that can transmit in only a single direction at a time. See duplex.

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 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.

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

A plate of electro-optical material that serves to rotate the plane of polarization of a light beam.

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...

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...

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...

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

A type of x-ray that is capable of deep penetration; its wavelength is about 10-8 cm.

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 direct-vision prism made in one piece that can be used only in parallel light.

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 lamp designed to emit a large amount of infrared radiation; used in applications requiring heat.

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,...

In reference to infrared, emissions that are like radio waves but that have a higher frequency.

A filter that allows heat radiation from an incident beam to pass without absorption or reflection.

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.

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.

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.

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

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...

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...

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.