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71 terms

Photonics Dictionary: R

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RED

radian energy distribution

red, green, blue

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,...

redshift

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...

reduced focal length

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...

reflection reduction coating

The thin, transparent film made up of specific substances applied to glass-air surfaces for the purpose of decreasing the amount of reflected light.

reciprocal megakelvin -> microreciprocal degree

An approximated measure of the smallest change in color temperature detectable by the human eye, defined as the reciprocal of the color temperature times 106. Also called mired or reciprocal...

reduced aperture

radargrammetry

The analysis of the photographs taken from the radar display of a survey aircraft and used when recording terrain that is obscured by clouds.

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...

radiant heat

Infrared radiation emitted from a source that is not heated sufficiently to give off visible radiation.

radiant intensity

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

radiation pyrometer

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...

radiation thermocouple

A thermocouple that is used in infrared spectroscopy to detect a sample's infrared emittance. See thermocouple.

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 telescope

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

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,...

Raman effect

When light is transmitted through matter, part of the light is scattered in random directions. A small part of the scattered light has frequencies removed from the frequency of the incident beam by...

Raman laser -> Raman effect

Raman scattering -> Raman effect

Raman spectroscopy

Raman spectroscopy is a technique used in analytical chemistry and physics to study vibrational, rotational, and other low-frequency modes in a system. Named after the Indian physicist Sir C.V. Raman...

random noise

Essentially, noise that cannot be predicted. Therefore, even if the magnitude of sound or oscillation in a system is known at a given moment, random noise can change in a short time.

rapid rectilinear lens

A double meniscus system in which two achromatized meniscus lenses are arranged symmetrically on either side of the aperture stop, reducing or eliminating distortion, coma and lateral color.

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,...

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 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...

reagent

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...

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...

recombinase polymerase amplification

Recombinase polymerase amplification (RPA) is a molecular biology technique used to rapidly amplify specific DNA or RNA sequences under isothermal conditions, meaning it does not require the...

reflecting microscope

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

reflective heat mirror -> diathermic mirror

A mirror coated to reflect cold (white) light while transmitting hot (infrared) energy.

reflective spectroscopy

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...

reflective

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...

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.

refractive index liquids

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...

refresh rate

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.

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.

remote active spectrometer

A device employed to identify toxic agents lingering on the ground or in the air from up to three miles away, by using laser beams to detect infrared light-absorption patterns that can be analyzed to...

remote inspection

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

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...

repeatability

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

resonance

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...

resonant cavity -> resonator

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...

resonator

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...

retina camera

A special-purpose camera used by ophthalmologists to photograph the retina of the eye. The optical system operates through the eye pupil, and the illuminant must be able to send light into the eye...

retrodirective reflector -> retroreflector

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...

retrofocus lens

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

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...

Photonics DictionaryR