Photonics Dictionary: A

Concerned with the transmission and reception of both sight and sound. An audiovisual system communicates pictorial images and audio signals.

The radiation-free transition that takes place within an ion, in which inner-shell vacancies in neutral atoms are filled by outer-shell electrons, thereby transferring energy to other electrons,...

The energy analysis of electrons released in a secondary step following initial excitation or ionization.

Augmented reality (AR) is a technology that integrates digital information, typically in the form of computer-generated graphics, images, or data, with the real-world environment in real-time. AR...

The indistinct, less luminous portion lying immediately outside an electric arc whose spectrum often differs from that of the core.

The strongest light emitted by the Earth's upper atmosphere. It most often can be viewed in the Arctic as the aurora borealis, and in the Antarctic as the aurora australis.

The green line, in the spectrum of the aurora borealis, that has a wavelength of 5577 Å; it is caused by a forbidden transition in oxygen.

A device for automatic exposure control in which a motor-driven diaphragm adjusts the aperture in response to a signal from a photocell detecting ambient light.

A spectrograph in which the refracted beam returns almost along the path traveled by the incident beam, and is brought to a focus by the lens that collimates the incident beam.

Technique of projecting an illuminated target at infinity and receiving the target image after reflection from a flat mirror surface.

An autocollimator is an optical instrument used for measuring small angular deviations with high precision. It operates on the principle of autocollimation, where a light source is directed onto a...

A signal-averaging device that improves signal-to-noise ratio by comparing a sampled signal with a time-delayed form of itself.

Autofluorescence refers to the natural emission of fluorescence exhibited by certain biological structures or molecules when exposed to light. Unlike fluorescence that results from the application of...

A means of adjusting the sharpness of an image automatically, with a sensor for estimating distance or contrast and a drive mechanism to adjust the lens. Active systems generate a light source to...

A CCD sensor that provides feedback to the motion control system for a telescope, allowing the telescope to follow a particular object or section of sky automatically.

The luminescence of a substance that is produced by energy within it (e.g., radioactive material).

Automated optical inspection (AOI) is a technology used in manufacturing processes, particularly in electronics, to automatically inspect and detect defects or anomalies in products. AOI systems use...

A method of producing an essentially constant output signal from an electronic circuit despite variations in the strength of the input signal.

A system for automatic industrial process control or measurement, consisting of an optical module for image acquisition, a segmentation processor to isolate the image from its background, and an...

In fiber optics, the use of a detector to study the range of refractive indices achieved at various wavelengths. This information is calculated electronically to establish the divergence between...

A direct reading spectrograph having a photomultiplier assembly in place of a photographic plate. The output from the photomultiplier assembly is received by a microammeter or a pen recorder.

Any photographic medium that, when chemically developed, produces an exact photographic reproduction of the original.

The photographic recording of the distribution and location of radioactive substances found in a specimen. The record formed is the autoradiograph.

A microscope to which a beamsplitter and illuminated reticle have been added to measure the radius of curvature of a spherical surface by locating both surface and center and calculating the distance...

A low-power telescope placed at the eyepiece of an optical system to increase overall magnification. Most often used to evaluate image quality.

A device that utilizes avalanche multiplication of photocurrent by means of hole-electrons created by absorbed photons. When the device's reverse-bias voltage nears breakdown level, the hole-electron...

In a pulsed laser, the pulse energy in joules times the repetition rate in hertz.

A receiver for optical communications systems consisting of a symmetric binary, pulse-code-modulated transmitter, a log-normal channel and an array of independent photocounting detectors that yield...

Eye blink or head movement in response to bright light. Aversion responses such as blinking are sufficient protection from less hazardous lasers, including Class 2 lasers. An eye blink can occur, at...

In astronomy, the method of deliberately viewing objects with peripheral vision to take advantage of the eye's greater sensitivity to faint light a few degrees from the optical center.

The number of molecules in one gram mole of a substance, numerically approximated by 6.02 x 1023.

A bundle of rays that originates from an object point on the optical axis of a lens system.

A lens aberration that causes axial light rays having different wavelengths to focus at various points along the axis.

In gradient index optics, a gradient profile in which the refractive index varies along the direction of light propagation, or optical axis. Axial gradient lenses can be used to correct spherical...

A method of designing lasers whereby the laser rod is cut into elliptical discs and cooled by running water over the disc surfaces. The cooling circuit decreases the radial temperature gradients in...

A paraxial light ray that extends from an object point on the optical axis.

The propagation constant evaluated along the axis of a waveguide, that is, in the direction of transmission. Also called axial propagation wave number.