Photonics Dictionary: R

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.

A lens or lens system used to transfer a real image from one point within an optical system to another, with or without magnifying it.

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 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...

A toric lens generated by rotating a specific cross section about an axis beyond its area and used in the formation of annular images.

A corrective lens system that is placed near the focal plane of a Newtonian telescope to increase its effective field of view by correcting for coma formed by the telescope's paraboloidal mirror.

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

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,...

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...

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

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.

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...

A metal device of convex or concave curvature to which lens castings or semifinished lenses are cemented with only their edges in contact with the device.

A microscope to which a beamsplitter and illuminated reticle have been added that is used to measure contact lenses.

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...

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.

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....

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...

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...

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...

The restriction of wavefront error to within a quarter of a wavelength of a true spherical surface to assure essentially perfect image quality.

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...

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

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.

The fundamental wavelength standard of time or frequency. An atomic standard, it is properly expressed as 9,192,631,770 times the frequency of the transition between the hyperfine structure levels of...

The radiation emitted in semiconductors when electrons in the conduction band recombine with holes in the valence band. If population inversion occurs between portions of the valence and conduction...

In a straight line. When applied to a lens, it indicates that images of straight lines formed by the lens are not distorted.

The scanning of a region in a given sequence of slender, straight parallel strips.

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...

An image-forming system that uses mirrors rather than lenses. Such objectives are frequently used for astronomical telescopes and in ultraviolet microscopes.

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...

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...

The ratio of the diameter of the entrance pupil in an optical system to the equivalent focal length of that system. The relative aperture is denoted as a fraction in which f, the equivalent focal...

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

A form of lens assembly used in a projection system to maximize efficiency and assure uniform illumination of the object being projected.

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...

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...