Photonics Dictionary

A compound lens combination whose astigmatic difference is zero for one or more off-axis zones in the image plane. In such a lens the other aberrations are sufficiently well-corrected to yield...

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

The angle formed between a refracted ray and the normal to the surface. This angle lies in a common plane with the angle of incidence. See also Snell's law of refraction.

An angstrom, symbolized by the Ångström or Å, is a unit of length used to express atomic and molecular dimensions. It is equal to 0.1 nanometers or 1 × 10-10 meters. The...

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...

The part of an electrical circuit in which the electrons leave (a cathode-ray tube) or enter (an electrolytic cell) a unit in the circuit.

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

In image processing, methods of reducing image defects that result from false data. Techniques include sampling, linear intensity, filtering a high-resolution image to produce a low-resolution image,...

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...

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 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...

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.

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

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...

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

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...

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...

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...

An argon-fluoride (ArF) excimer laser is a type of ultraviolet laser that operates using a mixture of argon and fluorine gases. Excimer lasers are a class of gas lasers that emit light in the...

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

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

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.

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...

A lens aberration that results in the tangential and sagittal image planes being separated axially.

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 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...

The Atmospheric Correction Now software (ACORN) is a tool used in remote sensing and satellite imagery processing. Its primary function is to correct satellite imagery for atmospheric effects that...

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...

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...

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...

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.

Attenuated total reflectance (ATR) spectroscopy is a technique used in analytical chemistry to obtain IR spectra of samples. It is particularly useful for analyzing solid and liquid samples without...

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...

An attenuator is an electronic or optical device used to reduce the power or intensity of a signal without significantly affecting its waveform or other characteristics. Attenuators are commonly used...

In the SI system, prefix meaning 10-18.