Photonics Dictionary: R

The astigmatism in a lens system that results when light enters the system at an oblique angle.

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...

A statistical analysis of facts obtained when the intensity of x-ray diffraction is calculated at different angles. In this way, the interatomic distances of gases and liquids can be deduced, with...

The detection and analysis of naturally formed extraterrestrial electromagnetic radiation within the radio frequency range of the spectrum.

A photographic camera and processing system used to form a usable record of the subject in a short time, usually a few seconds, for immediate analysis.

The pattern of lines traced by rectilinear scanning in display systems.

In imaging technology, a device that converts raster or line-scan data to pixel form for further processing.

A display in which regeneration takes place serially at a fixed speed in a set pattern through the scan lines.

The vertical or horizontal distance between two addressable points on a display screen; indicates the basic resolution element of a terminal.

An image that appears when a hologram is illuminated by a suitable light source, generally a laser beam.

Holographic quantity expressed as the ratio of the reconstructed first-order image to that of the incident reconstructing beam.

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...

The growth of particular grain fragments in a metal or alloy, at the expense of others, that occurs when the metal or alloy is severely worked, as by cold rolling. Recrystallization results in...

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

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.

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...

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

Image processing operations performed on one area of an image.

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

A crucible made of electrically resistive material through which a current is passed to heat the material inside, which then evaporates and is deposited as a thin film on a substrate. Resistance...

A device having electrical resistance and used in an electric current for purposes of protection, operation or control of current.

A test method for determining high-reflectivity levels by monitoring cavity decay within a resonant cavity formed by two mirrors under test.

An interferometric method for describing the surface shape of large coated or uncoated optical flats. The procedure uses a commercially available small-aperture phase-shifting interferometer for...

More efficient than the Foucault knife-edge test, this test examines curved mirrors by using a transmission grating with 40 to 200 lines per inch in place of the knife-edge, and a section or slit of...

Ability of a laser to resist variations in output power caused when it is slowly rotated about its optical or symmetrical axis.

In spectroscopy, the false images arranged symmetrically on both sides of the true line and caused by irregularities in the ruling of diffraction gratings.

RTSP, or real-time streaming protocol, is a network control protocol designed for controlling streaming media servers. It is used for establishing and controlling media sessions between endpoints....

A grating in which the wires or rods are set radially within a circular structure.

The deviation from the ideal case where a circular variable filter is located at a given wavelength along a radial line (or constant angle of rotation) regardless of the distance from the center of...

A reflecting optic whose reflectivity is a function of the radial distance from the optic axis; can be used to convert a Gaussian beam to one of uniform cross section.

Radiant power per unit source area per unit solid angle. Usually it is expressed in watts/m2/steradian.

Pertaining to electromagnetic radiation, with the contributions at all wavelengths of interest weighted equally.

Radiant power emitted into a full sphere (4p steradians) by a unit area of a source; expressed in watts per square meter.

The radiant energy emitted within a time period per unit solid angle, usually measured in watts per steradian.

An instrument used to recognize and identify incident radiation by the ionizing or stimulating properties of the radiation.

The average length in a specific material in which a relativistic charged particle will lose 67 percent of its energy by bremsstrahlung.

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.

Relative power distribution as a function of position or angle.

Also known as radiation thermometer. A pyrometer in which the radiant intensity from the source to be measured is used to calculate its temperature. The usual detector is a thermocouple, thermopile...

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...

Plates of glass containing as many heavy metal oxides as can be dissolved in the glass without causing devitrification. The glass is yellow, very heavy and has a high refractive index. It is almost...

An instrument designed to collect naturally formed extraterrestrial electromagnetic radiation within the radio frequency range of the spectrum in amounts sufficient to be measured.

A very uncommon lamp in which a tungsten electrode is heated to incandescence by a radio-frequency electrical current.

A radioactive element that is placed or injected into a system to obtain an autoradiogram of the system. It is used in a number of fields where standard methods of internal imaging, for example,...