Photonics Dictionary: R

A type of internal focusing in which only the lens elements closest to the rear of the lens barrel are moved.

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...

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...

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....

A plot showing how the response (ability to detect a signal) varies with wavelength. D(l).

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.

The spontaneous visual presentation of radar information by electronic traces on a cathode-ray tube.

An acronym for radioactive detection, identification and computation. The term refers to the detection and measurement of the intensity of emitted nuclear radiation.

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,...

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.

The emission and/or propagation of energy through space or through a medium in the form of either waves or corpuscular emission.

The force exerted on a surface by radiation.

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...

The film used in photographic dosimetry to record the types and amounts of ionizing radiation, such as x-rays and gamma rays, present in an area for a set interval of time. The negative produced by...

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

The frequency range for radio and television transmission.

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 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,...

An instrument used to detect radioactive materials: alpha particles or helium nuclei; beta particles or free electrons; and gamma rays, which are x-rays of very short wavelength. They may be detected...

The photographic image of a thin specimen having a radioactive isotope that, formed through contact between the specimen and a photographic plate, displays the distribution of the radioactive...

An x-ray or radium photograph illustrating the nonuniform density of the structure that the rays penetrate.

A solid-state panel of the photoconductor-electroluminescent type. The photoconductive layer, sensitive to x-rays, is coated by the electroluminescent, which gives the visible image. When the former...

Incapable of being penetrated by any form of radiation.

Capable of being penetrated by some form of radiation.

Essentially, a hologram of a hologram, in which the first-generation hologram is masked with a narrow slit. During image reconstruction, the slit operates as the exit pupil in image space. The...

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...

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...

An eyepiece consisting of two planoconvex lenses of the same focal length, with facing convex surfaces.

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.

Fiber optic cable in which the arrangement of fibers within the bundle has been made random so that output light will be uniformly distributed and not relay the image of the light source at the input...

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.

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 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,...

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

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...

A term that describes any state of glass before its manufacture as an element.

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...

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...

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 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 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...

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

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

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...