Photonics Dictionary: H

A satellite-borne remote sensing device capable of transmitting images at 10 and 20 m resolution from an altitude of 830 km, each sensor covering a ground area of 60 km, by means of a folded...

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...

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.

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...

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...

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.

Text or images printed on paper or another tangible medium, as opposed to those viewed electronically on a cathode-ray-tube screen.

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....

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

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.

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.

A glass filter that transmits visible light while absorbing infrared energy (heat).

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

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...

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.

Laser cavity bounded by a plane mirror and a concave spherical mirror with the plane mirror located at the center of curvature of the concave mirror.

Laboratory experiments that focus on demonstrating new capabilities of a certain technology or device, usually without consideration of industrial or commercial practicality.

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.

The ionization and spark emission due to exposure to ultraviolet radiation.

Radiation consisting of more than a single wavelength in the visible region of the spectrum.

In optical communications, the translation of optical signals into radio signals, lowering their frequency in detection from greater than 1014 Hz to less than 1010 Hz, so that further signal...

A junction between semiconductors that differ in their doping level conductivities, and also in their atomic or alloy composition.

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.

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 dynamic range (HDR) refers to a technology that allows for a broader and more dynamic range of luminosity in visual content, such as images or videos. It is particularly associated with displays...

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...

Distortion of the high frequencies of a signal. In television, the term generally applies to frequencies above the 15.7 kHz line frequency.

A cloud chamber designed to maintain the gas within it at a high pressure as a means of reducing the range of the high-energy particles and, subsequently, increasing the chances of observing...

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....

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...

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...

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.

An imaging device whose technology contributes three specific advantages: ability to study large solid specimens that exhibit behavior in bulk; conduction of in situ studies of radiation damage; and...

The portion of a reproduced image having the greatest luminance.

A fish-eye lens designed to photograph cloud formations over the entire visible sky.

Histochemical staining is a laboratory technique used in biology and medicine to visualize specific chemical components within biological tissues. This technique involves the application of various...

A graphic representation of a distribution function such as frequency by means of rectangles whose widths represent the intervals into which the observed values' range is divided and whose heights...

Histology is the branch of biology and medicine that involves the study of the microscopic structure of tissues and organs at the cellular and subcellular levels. It is a field that focuses on the...

A soft, malleable, stable rare-earth element. Holmium laser systems are used in surgical procedures involving the cutting and vaporizing of soft tissue, cartilage and calcific structures.

Holmium lasers are a type of medical laser that utilizes holmium-doped crystals as the gain medium. The term holmium laser is often associated with a specific type of laser used in urology for...

An interference pattern that is recorded on a high-resolution plate, the two interfering beams formed by a coherent beam from a laser and light scattered by an object. If after processing, the plate...