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74 terms

Photonics Dictionary: R

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rail -> optical bench

A support for optical parts comprising a solid bed that permits precise longitudinal movement of one component relative to the others, and a number of sliders equipped with holders for lenses, lamps,...

repeater -> optical repeater

In an optical fiber or waveguide communications system, an optoelectronic device or module that receives an optical signal, converts this optical signal to an electrical signal which is then...

rheinberg illumination -> optical staining

With respect to microscopy, also called dispersive staining, optical staining the projection of colors through areas of a colorless specimen by color filters that are constructed to fit over the...

racemic

Inactive optically, but having the capacity for resolution into forms of opposed optical activity. The term is derived from racemic acid, an optically inactive, tartaric acid.

radial distortion

An alteration in magnification from the center of the field to any point in the field, measured in a radial direction from the center of the field. Some radial distortion is inherent in most optical...

radial gradient

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,...

radiation mode

A mode in an optical waveguide whose fields are transversely oscillatory everywhere external to the waveguide. It exists even in the limit of zero wavelength.

radiation trapping

That process by which radiation spontaneously emitted by a volume of optical materials is resonantly reabsorbed within the same volume before it escapes. This effect is manifested in a reduction in...

radio-frequency discharge laser

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

Raman fiber probe

A flexible fiber cable with a small diameter that transports light from the excitation laser to the target. Used in Raman spectroscopy, the probe is capable of obtaining high-quality data at high...

Ramsden circle -> exit pupil

In a lens or other optical system, the image of the aperture stop as seen from image space.

rangefinder

1. An optical distance finder that depends on triangulation of two convergent beams on an object from disparate view points. 2. A device that depends on the measurement of time of wave travel from an...

rare earth dopants

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 doped fiber

An optical fiber in which ions of a rare-earth element, such as neodymium, erbium or holmium, have been incorporated into the glass core matrix, yielding high absorption with low loss in the visible...

rare-earth elements

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,...

rare-earth type glass

Optical glasses containing the oxides of rare earths such as lanthanum to impart a very high refractive index combined with a low dispersive power.

ray

A geometric representation of a light path through an optical device; a line normal to the wavefront indicating the direction of radiant energy flow.

Rayleigh scattering

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

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...

read screen

The transparent component of an optical reader that transmits the image rays of the characters to be read.

read-only memory

An optical storage product that can be used for playback only.

read-write capability

In an optical data storage system, denoting the optical head's ability both to record information and to detect it for playback.

read-write head

That part of a magnetic or optical tape or disc drive that retrieves data from or records data on the recording media.

real field -> true field

The size of the field of view in the object space of an optical system as differentiated from that in the image space (apparent field).

real image

An image that is formed when rays emerging from an optical system all converge to a point on the optical axis. A real image can be seen on a screen in the image space of the given optical system.

receiver

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

reciprocity law

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.

rectilinear system

An optical system that is corrected for distortion and spherical aberration and therefore forms the image of a straight line as a straight line.

reference surface

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.

reflectance confocal microscopy

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...

reflection grating

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...

refracted near-field scattering method -> refracted ray method

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...

refracted ray

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.

refracted ray method

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...

refractive index contrast

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...

regenerative amplifier

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.

registration shift

A shift in the apparent position of an object when an optical element is added or removed.

relative aperture

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...

relative intensity noise

The inherent laser amplitude noise relative to the average optical power produced by the laser; the RIN decreases rapidly as current is increased.

relay lens

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.

repeatability

The degree to which a predetermined or previous setting of a positioning device can be duplicated by observance of the optical phenomena.

replicated optics

Optical components, usually reflectors, produced using proprietary techniques that transfer the precision of a master to a number of elements.

residual absorption and scattering

Loss mechanisms that degrade the performance of all thin-film optical devices by removing radiant flux out of the specular beams.

residual blue

The optical phenomenon in which white light dispersed by small particles in suspension appears blue when viewed through a suitable Nicol prism.

residual gas analysis

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

resolution chart -> resolution target

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...

resolution target

resolution test chart -> resolution target

resolving power

A measure of an optical system's ability to produce an image which separates two points or parallel lines on the object. See Rayleigh criterion of resolving power.

resolving power chart -> resolution target

Photonics DictionaryR