Definitions: A

The elimination of magnetic moments and decrease in magnetic susceptibility with a decrease in temperature due to the equal power of atomic magnets.

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...

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...

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...

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.

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

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...

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...

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

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

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...

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...

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...

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.

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...

A gas, such as oxygen, that improves the speed and efficiency of a laser cutter or welder when applied to the work surface, or an inert gas, such as argon, that helps to clean or shield the work...

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

A camera designed to record astronomical objects (e.g., stars, planets, nebulae, galaxies) and their spectra.

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.

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.

An instrument that photographs the spectra of an extraterrestrial object.

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...

The unit generally used to express distances within the solar system, and sometimes to measure interstellar distances. Technically, one astronomical unit is the mean distance between the Earth and...

The scientific observation of celestial radiation that has reached the vicinity of Earth, and the interpretation of these observations to determine the characteristics of the extraterrestrial bodies...

A glass-ceramic material developed in Russia. Astrosital resembles Zerodur in terms of its ultralow thermal expansion. Other spellings include Astro-Sital and Astro-Sitall.

A method of data multiplexing that can provide large, instantaneous bandwidths for busy traffic while permitting slow traffic to use that bandwidth between bursts. Very short, fixed-length packets or...

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...

A range of wavelengths within which radiation transmitted through the atmosphere suffers relatively little absorption by atmospheric gases.

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...

An atomic clock is a highly precise timekeeping device that uses the vibrations or oscillations of atoms as a reference for measuring time. The most common type of atomic clock uses the vibrations of...

The analysis of fluorescence emitted by discrete atoms, in flames, that have absorbed radiation from an external source. It is used to study the physical and chemical processes that arise from...

An atomic force microscope (AFM) is a high-resolution imaging and measurement instrument used in nanotechnology, materials science, and biology. It is a type of scanning probe microscope that...

The efficiency of scattering by an atom in a particular direction, expressed as: where AA is the amplitude of the wave from the atom and AE is the amplitude of the wave from a free electron.