Photonics Dictionary: A

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

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.

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...

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.

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...

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 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.

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...

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

A vapor-phase oxidation process for fabricating graded-index optical fibers. It differs from outside vapor phase deposition in that the preform is developed radially rather than longitudinally. An...

An axicon is a type of optical component characterized by its conical shape and its ability to transform a collimated Gaussian beam of light into a ring-shaped beam with a gradually increasing...

A straight line, real or imaginary, passing through a body and indicating its center; a line so positioned that various portions of an object are located symmetrically in relation to the line. See...

Azadioxatriangulenium is a type of organic compound with a unique triangular molecular structure. It is often abbreviated as ADOTA. This compound belongs to the class of polycyclic aromatic...

1. In astronomy, the angle measured clockwise (eastward) in a horizontal plane, usually from north (true north, Y-north, grid north or magnetic north). 2. With relation to the plane-polarized light...

Azimuthal polarization refers to a specific polarization state of light where the electric field vector of the electromagnetic wave points along the azimuthal direction (around the propagation axis)....

Azobenzene is a chemical compound consisting of two phenyl rings linked by a N=N double bond. It is well-known for its ability to undergo reversible photoisomerization, meaning it can switch between...