Definitions: A

An opening or hole through which radiation or matter may pass.

A combination 80-column computer card containing a 35-mm microfilm frame. Reference data can be punched onto the card to facilitate retrieval of it on film.

The second adjustable iris diaphragm in an optical system. In the common microscope condenser system, it usually is located beneath the substage condenser on a transmitted light microscope. When the...

A loss of resolution or detail in a television signal caused by the size of the electron scanning beam.

The amplitude, polarization and phase contained in the field distribution over the aperture.

The formation of an image by a pinhole aperture that transmits radiation, such as gamma radiation.

Also known as a shadow mask, a perforated plate placed between the focusing and accelerating electrodes, and the tricolor phosphor screen in a color-television tube.

The ratio of the lens aperture to its focal length (1/f/#).

A physical constraint, often a lens retainer, that limits the diameter of the axial light bundle allowed to pass through a lens.

The point of a planet or comet's orbit that is farthest from the sun.

Also known as aplanatic lens. A lens corrected for spherical aberration and coma.

A system that satisfies the Abbe sine condition, and is free from spherical aberration and coma.

Aplanatic points refer to specific points in an optical system where certain aberrations, such as spherical aberration or coma, are minimized or eliminated. In an optical system, aberrations are...

An aplanatic surface is an optical surface that is specifically designed or shaped to minimize spherical aberration and coma. Spherical aberration is an optical aberration that occurs when light rays...

An apochromat, often referred to as an apochromatic lens or apochromatic objective, is a type of optical system designed to minimize chromatic aberration. Chromatic aberration occurs when different...

An optical system that is corrected chromatically for three colors simultaneously.

The use of a variable transmission filter at the aperture stop of a lens to modify its diffraction pattern. Reduced transmission at the center of the aperture will favor performance at high...

The point on an elliptical orbit about the Earth that is the farthest distance from the Earth.

A unit of luminance equal to 1/p candela per square meter.

The perceived brightness difference between light and dark areas on a target.

The angular subtense of the field of view in the image space of a telescope, as differentiated from that in the object space (the true field).

The perceived brightness of an object being viewed at some distance, especially through an optical instrument.

The visual perception of motion when fixed stimuli are exposed in rapid temporal and spatial succession.

The angle subtended by an object, determined by the size of the object and its distance from the viewer.

An aptamer is a short, single-stranded DNA or RNA molecule that can bind to a specific target molecule with high affinity and specificity. Aptamers are often referred to as chemical antibodies due to...

The transparent fluid that fills the portion of the eye between the cornea and the eye lens (the anterior chamber).

A bright spot or point, due to Fresnel diffraction, that appears at the center of the shadow of a circular object in light originating from a point source. Also referred to as a Fresnel spot or...

The electric arc that is a particular discharge between two electrodes in a gas or vapor which is characterized by high cathode densities and a low voltage drop.

An arc flash is a sudden release of electrical energy due to an electric arc — a continuous, high-current discharge of electricity between conductors or from a conductor to ground. Arc flashes...

In present usage, especially for spectroscopic identification, an arc between electrodes that serves as a radiation source. Gas tubes that contain mercury vapor and mixtures of helium, neon and argon...

The spectrum of the light produced by vaporizing an element in an electric arc.

Displacement in a direction perpendicular to that of the intended displacement, as in a translation stage with simple flexures that experiences vertical displacement during horizontal motion; it is...

The ratio of aperture area over receiving area for a specific lens. Also called geometric concentration.

Area scan, in the context of imaging and cameras, refers to a method of capturing an entire two-dimensional image in a single snapshot or exposure. Unlike line scan, which captures images one line at...

gas laser using ionized argon as the active medium and applying electronic excitation in order to produce the laser light

A protective jacket added to an optical fiber to facilitate use in harsh environments. Armor usually consists of steel or aluminum and is placed between the fiber and its outer jacket.

In image processing, a specially designed programmable computer peripheral that attaches to the host system for the purpose of more rapid arithmetical calculations than the latter can supply. The...

The plot that expresses a reaction rate vs. the reciprocal of absolute temperature. Often used to describe the thermal characteristics of laser applications such as ablation or annealing.

A dark red opaque material that is transparent to the infrared beyond 1 µm.

The ability of a machine to perform certain complex functions normally associated with human intelligence, such as judgment, pattern recognition, understanding, learning, planning, and problem...

iris or adjustable radially symmetric opening used for allowing the passage of useful light

Radioactivity formed by the bombardment of stable elements by either neutrons or high-energy, charged particles under regulated conditions.

A point source of light used for the test and evaluation of image quality. May be a backlit pinhole in an otherwise opaque sheet placed at an appropriately large distance from the lens being tested.

The particular orientation of the image, such as normal, canted, inverted or reverted.

With respect to pictorial displays, the ratio of the width to the height. The television standard in the US is 4:3. High-definition or wide-screen television will have a ratio of 16:9.

Not spherical; an optical element having one or more surfaces that are not spherical. The spherical surface of a lens may be slightly altered so as to reduce spherical aberration. Aspheric surfaces...

An optical system having one or more lens or mirror components that have nonspherical surfaces. These surfaces, whether reflecting or refracting, serve to advance or retard the incident wavefront,...

An aspheric lens is a type of lens whose surface profiles deviate from the traditional spherical shape. Unlike spherical lenses, which have a constant curvature across their surfaces, aspheric lenses...

An aspheric mirror is an optical mirror surface that deviates from the shape of a perfect sphere, having a non-spherical surface profile. Unlike traditional spherical mirrors, which have a curved...