Photonics Dictionary: R

The energy passed on as electromagnetic radiation; e.g., radio, heat or light waves.

Rabi oscillations are a fundamental phenomenon in quantum mechanics that describe the periodic and reversible exchange of energy between two quantum states when subjected to an oscillating external...

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

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

The time rate of flow of radiant energy, expressed in watts (W), and carries the units of Joule per second (J/s). The prefix often is dropped and the term "power" used.

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

The average length in a specific material in which a relativistic charged particle will lose 67 percent of its energy by bremsstrahlung.

A device used to accelerate the electrons in a free-electron laser by channeling microwave energy into waveguide cavity assemblies.

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...

The study of radioactive substances and high-energy radiations such as x-rays and g-rays.

Luminescence produced by the bombardment of radiant energy such as x-rays, radioactive waves or alpha particles.

A device used to measure the intensity of radiant energy.

The absorption of part of the photon energy by a molecule through which there is a slight energy change and the energy balance moves on.

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...

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,...

A geometric representation of a light path through an optical device; a line normal to the wavefront indicating the direction of radiant energy flow.

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...

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 type of conducting surface or material used to reflect radiant energy.

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.

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...

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...

One of the types of change in the energy levels of molecules or atoms in a laser that can result in lasing action. Because the energy levels between rotational states are small, such lasing action is...

The term "Rydberg atom" refers to an atom in a highly excited state where one or more of its electrons are in a Rydberg orbital. A Rydberg atom is characterized by having an electron orbit that is...