Photonics Dictionary: R

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.

Also known as display primaries. Colors formed by a television receiver that are of constant chromaticity and variable luminance, and that, mixed in certain proportions, form other colors. Red, green...

A detector and signal demodulator used in optical communications systems to receive a signal and often to translate it into an electronic signal.

The fundamental wavelength standard of time or frequency. An atomic standard, it is properly expressed as 9,192,631,770 times the frequency of the transition between the hyperfine structure levels of...

With respect to photography, the law stating that the optical density of an exposed emulsion with standard development is a function of just the irradiance and the exposure times.

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...

A reconfigurable optical add-drop multiplexer (ROADM) is a key component in wavelength-division multiplexing (WDM) optical communication networks. It allows for flexible and dynamic routing of...

A type of camera that incorporates a tiny mirror that oscillates in accordance with incoming signals. An illuminated slit is imaged by this tiny mirror on a moving ribbon of sensitized paper or film,...

In a straight line. When applied to a lens, it indicates that images of straight lines formed by the lens are not distorted.

Straight line travel. This denotes the fact that light travels in a straight line when traveling through a medium with a constant refractive index.

The scanning of a region in a given sequence of slender, straight parallel strips.

RGB stands for red, green, blue, which are the primary colors of light used in additive color mixing. The RGB color model is widely used in various electronic displays, such as computer monitors,...

The displacement of spectrum lines, as determined by the increasing distance between, and the relative velocity of, the observer and a light source, causing the lines to move toward the red portion...

The ratio of the first focal length of a lens to the refractive index of the medium containing the incident light; the ratio of the second focal length to the refractive index of the medium...

The point of a chromaticity diagram that represents the chromaticity of a reference stimulus.

The surface of an optical fiber that is used as a reference when joining optical fibers. Although the outermost cladding is usually used, the core cladding surface is also a common reference point.

The light from a nonselective diffuse reflector due to the standard illumination of the scene to be televised.

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...

An exposure meter that indicates the amount of light reflected from the subject of interest.

An image-forming system that uses mirrors rather than lenses. Such objectives are frequently used for astronomical telescopes and in ultraviolet microscopes.

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...

The thin, transparent film made up of specific substances applied to glass-air surfaces for the purpose of decreasing the amount of reflected light.

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...

Thin-film coating, single or multilayer, that is applied to a substrate to increase its reflectance over a specified range of wavelengths. Metal film, transparent or opaque, is the oldest form of...

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...

The term reflective is an adjective that describes the ability of a surface or material to reflect light or other forms of radiation. It implies the capability of bouncing back or redirecting...

An instrument for measuring reflectance.

A transparent sphere that has an index of refraction that is different from that of the medium surrounding it; used in optics to demonstrate refraction and astigmatic image formation.

An instrument used to measure the refractive index of solids and liquids. Several types exist, the most common being the Abbe refractometer.

The method used to determine the refractive index of a given substance.

The ratio of the diameter of the entrance pupil in an optical system to the equivalent focal length of that system. The relative aperture is denoted as a fraction in which f, the equivalent focal...

A plot showing how the response (ability to detect a signal) varies with wavelength. D(l).

The steady state of temperature exhibited by a material that has absorbed and emitted radiation equally.

A form of lens assembly used in a projection system to maximize efficiency and assure uniform illumination of the object being projected.

A lens or lens system used to transfer a real image from one point within an optical system to another, with or without magnifying it.

The discernment of depth or apparent difference in distance that causes the object to stand out from its background because of stereoscopic vision. The impression of relief can be obtained from the...

A display device, such as a cathode-ray tube, that is located at some distance from the source generating the displayed information.

Remote inspection refers to the process of inspecting, evaluating, or monitoring assets, equipment, infrastructure, or systems from a distance, typically using remote sensing technologies and...

Remote sensing is a method of data collection and observation where information about objects, areas, or phenomena on Earth's surface is gathered from a distance, typically using sensors onboard...

A pulsed laser that emits a recurring pulsed output. Frequency of the pulses emitted is known as pulsed recurrence frequency (PRF). When the PRF or duty cycle is very high, repetitively pulsed lasers...

A reproduction made of an original grating -- usually by casting thermosetting plastics onto the original -- to avoid the high expense of making the original gratings.