Definitions: R

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...

In holography, the beam of light that is directed from the beamsplitter to the recording medium, where it interferes with the object beam to generate the hologram.

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.

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...

The output of spectral channels written as an integral function of known solar irradiance, atmospheric transmittance and camera spectral responsivity, and the unknown spectral reflectance.

Ratio of the directionally reflected flux to that reflected in the same direction by a perfect reflecting diffuser identically irradiated or illuminated.

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.

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

A photographic method used to obtain an image of a subject by means of its reflectance of incident ultraviolet radiation. An ultraviolet source is used to irradiate the subject, while the reflected...

A galvanometer having a small mirror that is mounted on a moving element and that reflects a light beam onto a scale.

A microscope that uses a reflecting objective; often used with ultraviolet or infrared radiation.

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

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...

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...

Parametric measurement for elliptical fiber and cable expressed as a ratio of the two-directional flow of power through the cable at any chosen point.

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...

A hologram that is illuminated by a source from the viewer's side.

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...

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

An instrument for measuring reflectance.

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

A lamp used in projection that is made with a reflector built into the bulb, normally by coating a portion of its interior with a reflective material to ensure the reflector's optimum position in...

A light ray that has had its direction altered because of its traversing an air-to-glass interface at some angle. In an optical waveguide, a ray that is refracted from the core into the cladding.

The technique for measuring the index profile of an optical fiber by scanning the entrance face with the vertex of a high numerical aperture cone and measuring the change in power of refracted...

A wave of radiation that has undergone refraction.

A prism that often is used as a dispersing element in spectrographs and monochromators.

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.

The bending of oblique incident rays as they pass from a medium having one refractive index into a medium with a different refractive index.

A measure of the relative difference in refractive index between two optical materials. Most commonly used in fiber optics where the refractive index contrast, D, is given as follows: where n1 equals...

A closely spaced series of well-known chemicals having a refractive index lying between 1.33 for water and 1.95 for a solution of phosphorus in carbon disulfide. They are used to identify powdered...

The description of the refractive index along a fiber diameter.

The mean square difference in refractive index for two separate points in space.

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.

Rate at which an image on a computer screen is redrawn (usually 50 or 60 Hz) to prevent flicker caused by the decay of the visual image.