Photonics Dictionary: R

A type of internal focusing in which only the lens elements closest to the rear of the lens barrel are moved.

The formation of a distinct, irregular surface pattern on a photographic emulsion due to differential swelling of the gelatin.

Also known as reversed telephoto lens. A lens consisting of an ordinary objective with a negative component near its front focal point. Thus, the back focus is large, relative to its focal length....

A term describing a type of scratch.

A reticle, also known as a reticule or graticule, is a pattern or set of markings placed in the focal plane of an optical instrument, such as a microscope, telescope, riflescope, or camera, to...

The analysis of the photographs taken from the radar display of a survey aircraft and used when recording terrain that is obscured by clouds.

A statistical analysis of facts obtained when the intensity of x-ray diffraction is calculated at different angles. In this way, the interatomic distances of gases and liquids can be deduced, with...

In gradient index optics, a gradient profile in which the index varies in a direction perpendicular to the optical axis. Radial gradient lenses can focus light even when the lens surfaces are flat,...

A grating in which the wires or rods are set radially within a circular structure.

The deviation from the ideal case where a circular variable filter is located at a given wavelength along a radial line (or constant angle of rotation) regardless of the distance from the center of...

The emission and/or propagation of energy through space or through a medium in the form of either waves or corpuscular emission.

Also known as radiation thermometer. A pyrometer in which the radiant intensity from the source to be measured is used to calculate its temperature. The usual detector is a thermocouple, thermopile...

A gas laser in which the electrodes are mounted perpendicular to the optical resonator.

A very uncommon lamp in which a tungsten electrode is heated to incandescence by a radio-frequency electrical current.

The luminescence displayed when particular minerals are irradiated with β-rays and g-rays, after being exposed to nuclear radiation.

A metal device of convex or concave curvature to which lens castings or semifinished lenses are cemented with only their edges in contact with the device.

The absorption of part of the photon energy by a molecule through which there is a slight energy change and the energy balance moves on.

Raman spectroscopy is a technique used in analytical chemistry and physics to study vibrational, rotational, and other low-frequency modes in a system. Named after the Indian physicist Sir C.V. Raman...

A double meniscus system in which two achromatized meniscus lenses are arranged symmetrically on either side of the aperture stop, reducing or eliminating distortion, coma and lateral color.

Rare earth dopants refer to elements from the lanthanide series, also known as rare earth elements, that are intentionally introduced into the crystal lattice of a material to modify its properties....

Rare-earth elements (REEs) are a group of seventeen chemical elements found in the Earth's crust, characterized by their unique properties and scarcity relative to other elements. Despite their name,...

Ratiometry is a technique used in various scientific fields, particularly in analytical chemistry and biochemistry, to measure concentrations or quantities by comparing the intensity of two different...

Ray tracing is a rendering technique used in computer graphics to simulate the way light interacts with objects in a scene. It involves tracing the path of rays of light as they travel through a...

When a lens system with a circular aperture is free of aberrations, the image of a point object will appear as a disc of finite size surrounded by concentric rings. When two points are separated such...

In the region of a Gaussian beam focus by a diffraction-limited lens, it is the axial distance from the point of minimum beam waist (Wo) to the point where the beam diameter has increased to .

Rayleigh scattering is a phenomenon that occurs when light waves interact with particles or molecules that are much smaller than the wavelength of the light. It is named after the British scientist...

Reactive evaporation refers to a process in thin-film deposition where a material is deposited onto a substrate through evaporation, and chemical reactions take place during or after the evaporation...

In chemistry, a device in which a chemical reaction takes place. In electronics, a device that introduces reactance into a circuit.

A reagent is a substance or compound that is used in a chemical reaction to bring about a specific transformation or to detect the presence or absence of another substance. Reagents are employed in...

The restricting opening at the rear of a lens or prism that is commonly defined as the maximum diameter of the emergent cone for the specified field of view, at infinity focus.

Recombinase polymerase amplification (RPA) is a molecular biology technique used to rapidly amplify specific DNA or RNA sequences under isothermal conditions, meaning it does not require the...

The radiation emitted in semiconductors when electrons in the conduction band recombine with holes in the valence band. If population inversion occurs between portions of the valence and conduction...

The growth of particular grain fragments in a metal or alloy, at the expense of others, that occurs when the metal or alloy is severely worked, as by cold rolling. Recrystallization results in...

The ratio of reflected flux to incident flux. Unless otherwise specified, the total reflectance is meant; it is sometimes convenient to divide this into the sum of the specular and the diffuse...

Reflectance confocal microscopy (RCM) is a non-invasive imaging technique that allows for high-resolution, in vivo imaging of biological tissues at the cellular level. It is particularly useful in...

An instrument that spectrally analyzes the flux reflected from a material. The reflected flux may be total, diffuse or specular. Often the instrument measures the reflectance factor instead of the...

A solar spectrograph that uses long focus concave mirrors as its collimator and camera element.

A telescope that uses a reflecting objective to focus an image of a distant object at a focal point.

Return of radiation by a surface, without change in wavelength. The reflection may be specular, from a smooth surface; diffuse, from a rough surface or from within the specimen; or mixed, a...

A reflection grating is an optical component that consists of a series of closely spaced, parallel reflecting surfaces or grooves. These grooves are typically ruled or etched onto a flat substrate or...

A means of high resolution study through the application of soft and hard x-rays onto a sample surface in order to obtain image information from 1-10 nm layers and surfaces. The x-ray source emission...

Reflectance spectroscopy is a technique used to analyze the reflective properties of materials across various wavelengths of the electromagnetic spectrum. By measuring the reflectance of light from a...

A type of multiple-pass amplifier in which no optical leakage is allowed until a finite number of passes has occurred; at this time the entire cavity output is released as one pulse.

A figure of merit corresponding to the amount of light seen by a viewer through binoculars. A higher number indicates a brighter image in low-light situations. The relative brightness value is...