Photonics Dictionary: A

An oven or furnace that possesses the design requirements and heat control necessary to anneal glass for the optical industry.

Gamma ray radiation released when matter and antimatter, such as electron and positron, unite and eliminate each other, transforming completely into energy. The resulting gamma ray spectrum depends...

A type of solar eclipse that occurs when the sun is at perihelion and the moon is at apogee. Because the apparent size of the moon is insufficient to cover the sun, the outer edge of the solar disc...

An optical instrument that uses a yellow light of varying intensity with red and blue lights of fixed intensity to test for colorblindness.

Dispersion that occurs when the medium's index of refraction decreases as the frequency of the propagating light increases. For a given medium, some wavelength ranges may produce anomalous dispersion...

Color vision whereby abnormal proportions of three colors are needed for color matching.

An antigen is any substance that is capable of triggering an immune response in an organism. Antigens are typically proteins or large polysaccharides, although other types of molecules can also act...

A waveguide that has a core with a lower refractive index than the refractive index of the cladding. This structure can limit the power of the transmitted beam by removing unwanted radiation, for...

Light-absorbing material that is applied to the back support of any bright image under inspection to prevent the formation of a secondary image.

An antireflection coating (AR coating) is a thin film or coating applied to optical surfaces, such as lenses or windows, to minimize unwanted reflections and increase the transmission of light...

An electrically conductive layer for carrying off static charges that might accumulate on a surface.

An APD detector, or avalanche photodiode detector, is a type of photodetector used to detect light or optical signals by converting incoming photons into electrical current. It operates based on the...

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/#).

Also known as aplanatic lens. A lens corrected for 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...

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...

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 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...

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 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.

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...

The modification of the spherical surfaces in an optical system to correct for spherical aberration.

In an astigmatic grating, the image of the entrance slit located at the primary focus.

A cylindrical lens that may be rotated to distort a bundle of light originating at a point source, to form a line image.

In the discharge of a vacuum tube, the narrow, nonluminous region that sometimes may be found between the cathode and its glow.

An astronomical mirror, also known as a telescope mirror or primary mirror, is a key component of a reflecting telescope. It serves as the primary optical element responsible for gathering and...

A facility designed for the observation and recording of astronomical phenomena.

The use of photographs to record astronomical objects and phenomena for purposes of physical observation and measurement of motion, radiation and spectra.

The process of using a spectrograph with a telescope to acquire information on an astronomical object's speed and physical characteristics.

An astronomical telescope is a type of optical instrument designed to gather and magnify light from distant celestial objects for observation and analysis. It typically consists of two main optical...