Photonics Dictionary: R

A unit of energy absorbed from ionizing radiation, equal to 100 ergs per gram of irradiated material.

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...

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...

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 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 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...

A reflecting prism that is rhomboidal in shape. It has two parallel transmitting faces, and two parallel reflecting faces; the latter are oblique to the former (usually but not necessarily at...

A ring laser gyroscope (RLG) is a type of gyroscope that uses laser light to detect and measure changes in orientation. It operates based on the Sagnac effect, which is a fundamental principle of...