Photonics Dictionary: R

The coherent wave used to play back a recorded hologram. It is identical to the reference wave used in the generation of the original hologram; part of it is diffracted by the recording medium and...

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,...

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

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...

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...

The light ray leaving a reflecting surface, indicating the path of light after reflection.

A prism having several plane polished surfaces, some to transmit light, some to reflect light, and some to serve both functions in succession. It acts generally as a group of plane mirrors held in a...

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...

An echelon in which the dihedral angle between the faces of the groove is 90°.

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...

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...

The ratio of the intensity of the total radiation reflected from a surface to the total incident on that surface.

A type of conducting surface or material used to reflect radiant energy.

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...

The ratio of the velocities of light in two adjacent media, neither of which is air.

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

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...

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 measurement in optical thin-film coating processes whereby the gases remaining in the vacuum chamber after coating are characterized by mass spectroscopy.

1. In optics, the ability of a lens system to reproduce the points, lines and surfaces in an object as separate entities in the image. 2. The minimum adjustment increment effectively achievable by a...

A chart on paper or glass containing a series of sets of lines at progressively smaller spacing and used to ascertain the limiting number of lines per millimeter that an optical system is capable of...

Resonance can be defined in various contexts, including physics, chemistry, and music. Here are definitions for resonance in a few different fields: Physics: In physics, resonance refers to the...

A resonator is a device or system that exhibits resonance, which is a phenomenon that occurs when an external force or stimulus is applied at a specific frequency, causing the system to oscillate...

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

1. The photosensitive membrane on the inside of the human eye. 2. A scanning mechanism in optical character generation.

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....

Retroreflection is a phenomenon in optics where light is reflected back toward its source, typically in a direction nearly parallel to the direction from which it originated. This occurs due to the...

Retroreflectivity refers to the property of a surface or material to reflect light back to its source, regardless of the angle of incidence. Unlike most surfaces that scatter light in various...

A retroreflector is an optical device or structure that reflects incident light or electromagnetic waves back to their source, regardless of the direction from which the light approaches. Unlike...

A sequential scanning device, utilizing a revolving lens, in which the cathode-ray tube image is transformed into a circle of fibers. The rotating lens focuses each fiber successively on a multiplier...