Photonics Dictionary: A

A system used for measuring direct solar radiation.

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...

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...

Irregular propagation of a wave due to variations in the medium's density or refractive index.

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...

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

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

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

Any irregular motion, variation in intensity or change in color that arises because of atmospheric turbulence during the observation of an astronomical phenomenon or object.

A mode of data transmission whereby each bit of information is generated separately, with some stop/start code to indicate the interval between bits.

Compilation of the Air Force Cambridge Research Laboratories that contains values of the line parameters of the 1-0 bands of 12C16O. Because of the high accuracy of this record, calculated spectra...

The reduction in luminance of a light beam due to absorption and scattering as it passes through the atmosphere.

Formulaic compensation to correct laser ranging data for the effects of horizontal refractivity gradients; it requires the horizontal pressure and temperature gradient at laser sites, which are...

An atomic absorption spectrometer (AAS) is an analytical instrument used to determine the concentration of specific chemical elements in a sample by measuring the absorption of light at...

The analysis of the atomic structure of a sample by means of a source radiation that is absorbed and emitted by the sample with lines corresponding to the number and arrangement of atoms. Generally a...

Spectrometric analysis of the distinct and characteristic spectra of atoms of elements. The atoms are energized to emit radiant energy, which, when dispersed by a prism or diffraction grating,...

Attenuation refers to the gradual loss or reduction of intensity, force, or magnitude of a particular property as it propagates through a medium or travels over a distance. This concept is prevalent...

The rate of diminution of average optical power and the sum of the scattering and absorption coefficients.

The real part of the axial propagation constant for a particular mode. The attenuation coefficient for the mode power is twice the attenuation constant.

A device used to measure power loss in fiber optic connectors, cables or systems.

In fiber optics, the limitation on performance imposed by the amplitude of a received signal rather than distortion.

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

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 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...

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 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...

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)....

A thermoplastic or optically transmitting hard plastic produced by applying polymerization initiator and heat to a monomer.

The study of chemical changes produced by radiation.

Adaptive optics (AO) is a technology used to improve the performance of optical systems by reducing the effects of atmospheric distortions. The Earth's atmosphere can cause light passing through it...

The code signifying the location of the information being sought on a CD-ROM.

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 two-lens arrangement intended to image light into a microscope slide sample. The primary aberrations present are red and blue rings observed around the image focus.

A dispersion relation defined in order to value the reciprocal amount of dispersion. It is defined as the refractivity over the difference in index values of the shortest and longest visible...

A form of roof prism used to invert an image. The prism has faces cut normal to the optical axis; therefore, the prism may be placed within the optical path of a system and invert the image without...

Device which measures the index of refraction of glass as well as the dispersion over visible range.

A reflecting prism that inverts the image. The image is reflected four times internally and emitted laterally. The prism is cut normal to the optical axis while the image is internally reflected from...

A high-brightness, short-duration source in which low-pressure gas initiates the discharge to vaporize material from the tube wall, leading to a high-pressure discharge of ionized wall material.

The alteration and reduction of color with the addition of white light. The perceived color shift that occurs as the monochromatic-white combination meets the eye and is interpreted by the brain. The...