Photonics Dictionary: A

Location on the CIE chromaticity diagram which produces the color white for a given light source at a specified temperature.

The point to which the extension of the straight line, reaching from the sun to the observer's eye after penetrating the atmosphere of the Earth, is projected.

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...

The value of the distance of distinct vision, minimum focusing distance or near point, divided by the focal length of the lens. Magnification is produced when the optic is placed at its focal...

The measurement of heat energy as determined from absolute zero as the zero point on the scale. Increments are identical to the Celsius as well as Kelvin scales.

An absorption peak refers to a sharp increase or spike in the absorption of electromagnetic radiation at a particular wavelength or energy level. It is a distinctive feature in the absorption...

An achromat, in the context of optics, refers to a type of lens or lens system designed to reduce chromatic aberration. Chromatic aberration is an optical phenomenon where different colors of light...

That point in the electromagnetic spectrum at which an optical system focuses the most chemically effective rays.

In aerial photography, the geometric method of indicating the three-dimensional location of ground points from a pair of aerial photographs.

An optical system with object and image points at infinity. Literally, "without a focal length."

The angle formed between a ray of light striking a surface and the normal to that surface at the point of incidence.

The angular spectrum approach is a mathematical and computational technique used in the field of optics to analyze and simulate the propagation of optical waves, particularly in the context of wave...

Anisotropy refers to the property of exhibiting different values or characteristics when measured in different directions. In various fields, including physics, materials science, and geology,...

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

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...

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

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...

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...

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.

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

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...

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...

The unchanging nature of spectral reflectance as vegetational density increases to the point where additional increases in leaf area index or biomass do not cause a change in the spectral reflectance.

The area of optics in which the wave nature of a particle is exploited to carry out very accurate interferometry and other optical techniques with atoms instead of photons. In this process, particles...

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 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.

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

An optical device that produces a line image lying along the axis from a point source of light; therefore, it has no definite focal length. A lens with a weak conical surface on one face.

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)....