Definitions

A single-anode mercury pool tube that is designed to maintain a continuous cathode spot.

The angle between a light ray emerging from an optical system and the optical axis of that system.

In a lens or other optical system, the image of the aperture stop as seen from image space.

Flux leaving a surface per unit area.

The light spectrum formed by an explosive reaction or by the electrical explosion of a metallic wire by a strong current.

In cosmology, a star that exhibits a rapid increase in the magnitude of light, which is followed by a slow decrease in magnitude. The nova and supernova are explosive variables.

In optics, the total radiant energy incident on a surface-per-unit area. It is equal to the integral over time of the radiant flux density. Also known as radiant exposure.

A measure of film speed sensitivity to light.

An instrument used to measure the light from a scene to be photographed and to indicate the camera lens and shutter settings required to expose the film correctly. The exposure time required in a...

The length of time during which the receiver is irradiated.

A radiation source that, unlike the point source, can be resolved by the naked eye into a geometrical image.

1. A strainmeter capable of measuring the change in the relationship between two reference points, provided that the points are separated by at least 20 to 30 m. 2. An instrument used to determine...

The ejection of electrons from the surface of a solid by the absorption of a sufficient amount of photons.

1. The near total absorption of plane-polarized light by a polarizer that has an axis perpendicular to the plane of polarization. 2. The decrease in the intensity of a diffracted beam resulting from...

A type of exposure meter that artificially reduces the light admitted in a sequence of known fractions until a value is reached that is equivalent to the proper exposure.

The ratio of the power of a plane-polarized beam that is transmitted through a polarizer placed in its path with its polarizing axis parallel to the beam's plane, as compared with the transmitted...

The lowest anode voltage at which a gas tube can sustain a discharge.

A cement used to reduce crosstalk in fiber optic bundles or plates.

A ray that has a nonisotropic speed in a doubly refracting crystal. It does not necessarily obey Snell's law upon refraction at the crystal surface.

Radiation that is emitted by a source outside the Earth and its atmosphere.

Extreme ultraviolet (EUV) refers to a specific range of electromagnetic radiation in the ultraviolet part of the spectrum. EUV radiation has wavelengths between 10 and 124 nanometers, which...

A photodetector composed of a semiconductor material whose responsive properties can be altered by the addition of impurities to the basic material. Copper- and mercury-doped germanium are both...

A type of optical fiber loss resulting from the misalignment of fibers in a splice or connector.

Synonym of extrinsic fiber loss.

Photoconductivity due to the addition of impurities or external causes.

The properties exhibited by a semiconductor as the result of its modification by imperfections and impurities in the crystal.

The organ of vision or light sensitivity.

The area in a 2-D or 3-D microdisplay viewer within which the eye can move and still see the entire image.

A shield of rubber, plastic or metal used to protect the eyes of the observer from stray light and wind, and to maintain the proper eye distance.

The lens of an eyepiece nearest the observer's eye.

A pattern on an oscilloscope display that consists of a string of shapes that resemble eyes. Because the pattern becomes more closed with increasing distortion and interference, an open eye diagram...

Also termed eye distance. The distance between the vertex of the last optical surface of a visual optical system and the system's exit pupil.

Instruments used by ophthalmologists and optometrists to study the eye. There are, for instance, the ophthalmoscope to observe and photograph the retina; the retinoscope and optometer to determine...

An optical device used to monitor movement of the human eye.

Wavelengths between 400 and 1400 nm (VIS to NIR) are focused onto the retina by the cornea. Because the retina is sensitive to light, these wavelengths can be damaging even at low energies. It is the...

Also known as ocular. The lens system used between the final real image in a visual optical system and eye. It acts as an image magnifier. Many types of eyepieces are known; e.g., the Huygens used in...

The expression denoting the ratio of the equivalent focal length of a lens to the diameter of its entrance pupil.

An f-theta lens, also known as an f-theta scan lens or simply an f-theta lens system, is a specialized optical component used in laser scanning systems, particularly in laser marking, engraving, and...

An optical resonator in which feedback is accomplished by two parallel planes. In diode lasers, the planes are obtained by cleaving, polishing, etching, etc.

A nonabsorbing, multireflecting device, similar in design to the Fabry-Perot interferometer, that serves as a multilayer, narrow-bandpass filter.

The series of rings when monochromatic light passes through a Fabry-Perot interferometer.

A multiple-beam interferometer, usually consisting of two flat plates, with high reflective ability. The plates are set parallel to one another by spacers so that lightwaves may bounce back and forth...

A laser oscillator in which two mirrors are separated by an amplifying medium with an inverted population, making a Fabry-Perot cavity. Standard diode lasers are Fabry-Perot lasers.

A means of determining a prism's index of refraction by placing the prism so that its emergent face is perpendicular to the incident beam. This arrangement permits the determination of the prism's...

A highly reflective mirror that is usually flat on one surface and curved on the other, and that has silver, gold or aluminum deposited on glass, providing about 99 percent reflection.

The spectroscopic analysis of interference patterns using a monochannel spectrometer, spectrograph or multichannel spectrometer with a Fabry-Perot interferometer to record the fringes.