Photonics Dictionary: R

Return of radiation by a surface, without change in wavelength. The reflection may be specular, from a smooth surface; diffuse, from a rough surface or from within the specimen; or mixed, a...

Parametric measurement for elliptical fiber and cable expressed as a ratio of the two-directional flow of power through the cable at any chosen point.

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...

Thin-film coating, single or multilayer, that is applied to a substrate to increase its reflectance over a specified range of wavelengths. Metal film, transparent or opaque, is the oldest form of...

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...

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...

A lamp used in projection that is made with a reflector built into the bulb, normally by coating a portion of its interior with a reflective material to ensure the reflector's optimum position in...

A prism that often is used as a dispersing element in spectrographs and monochromators.

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...

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...

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.

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

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 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...

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

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.

1. In optics, the ability of a lens system to reproduce the points, lines and surfaces in an object as separate entities in the image. 2. The minimum adjustment increment effectively achievable by a...

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...

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.

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...

The re-emission of absorbed energy, having the same wavelength as the incident energy, in an arbitrary direction from a particle because of an energy level transition within the material.

In atomic fluorescence spectroscopy, fluorescence emitted by an atom at a spectral line of a wavelength identical to that of the stimulating radiation.

A type of ultrasensitive laser spectroscopy that can detect quantities as small as a single atom of some substances and that can differentiate between isobars of different elements.

That radiation emitted by an atom or molecule that has the same frequency as that of an incident particle; e.g., a photon. It generally involves a transition to the lowest energy level of the atom or...

The fluorescent emission spectrum emitted by certain substances following the irradiation of one of these substances with light that is of the same wavelengths as its fluorescence.

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...

The absorption of a material by a medium or system that has formerly been released from absorption by that same medium or system.

The number of electrons emitted per photon incident upon a photodetector.

A reticle, also known as a reticule or graticule, is a pattern or set of markings placed in the focal plane of an optical instrument, such as a microscope, telescope, riflescope, or camera, to...

The formation of a distinct, irregular surface pattern on a photographic emulsion due to differential swelling of the gelatin.

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...

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 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...

Retroreflectivity refers to the property of a surface or material to reflect light back to its source, regardless of the angle of incidence. Unlike most surfaces that scatter light in various...

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...

A prism made of two elements cemented together that, depending on its orientation, inverts or reverts an image. It may be used in converging or diverging light. Sometimes referred to as a K prism.

A sequential scanning device, utilizing a revolving lens, in which the cathode-ray tube image is transformed into a circle of fibers. The rotating lens focuses each fiber successively on a multiplier...