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Photonics Dictionary: R

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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.
In a gas, the temporary drop in density caused by contact with a sound wave.
remote active spectrometer
The pattern of lines traced by rectilinear scanning in display systems.
raster image processor
In imaging technology, a device that converts raster or line-scan data to pixel form for further processing.
raster scan display
A display in which regeneration takes place serially at a fixed speed in a set pattern through the scan lines.
Raster scanning
Raster scanning is a technique used in imaging and scanning systems to systematically capture and process information from a two-dimensional area or surface. It involves moving a sensor or scanning...
raster unit
The vertical or horizontal distance between two addressable points on a display screen; indicates the basic resolution element of a terminal.
An electronic device that minimizes short-term drift effects and random measurement error inherent in alternate ellipsometric measurement of two signals.
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...
raw glass
A term that describes any state of glass before its manufacture as an element.
A geometric representation of a light path through an optical device; a line normal to the wavefront indicating the direction of radiant energy flow.
ray intercept plot
A graph of the intersections of a fan of rays with the final image plane, plotted as a function of the positions of the rays in the pupil of the system.
ray tracing
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...
Rayleigh criterion of resolving power
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...
Rayleigh interferometer
A device that is used to determine the index of refraction of a gas or liquid through the interference patterns formed by two beams of light, one of which has been transmitted by the sample. A single...
Rayleigh limit
The restriction of wavefront error to within a quarter of a wavelength of a true spherical surface to assure essentially perfect image quality.
Rayleigh line
That element of a spectrum line in scattered radiation having a frequency equal to that of the corresponding incident radiation, due to ordinary or Rayleigh scattering.
Rayleigh prism
A prism system designed to produce a very high dispersion of light.
Rayleigh range
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
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...
radar bright display equipment
regional Bell operating company
Rutherford backscattering spectrometry
return beam vidicon
Rockwell hardness
reaction chamber; resistance × capacitance
radar data acquisition
rapid display system
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...
In chemistry, a device in which a chemical reaction takes place. In electronics, a device that introduces reactance into a circuit.
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.
reading glass
A low-power magnifier that usually has a large diameter.
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...
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 holographic image -> conjugate holographic image
Also known as real holographic image. The indistinct, highly distorted image produced on the side of the hologram closest to the observer, in addition to the primary image. When the location of the...
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.
real image
real-time processing
The ability of a vision system to interpret an image in a short enough time to keep pace with most operations.
A nonhomogeneity of index in flat glass that is in the form of an approximately plane layer.
rear facet monitor
A photodetector mounted in the same package as a laser diode that is positioned to monitor the output from the rear facet of the diode.
rear focusing
A type of internal focusing in which only the lens elements closest to the rear of the lens barrel are moved.
rear operating aperture
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.
receiver primaries
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.

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