Photonics Dictionary: R

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

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

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...

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 photographic process using x-ray radiation or the g-rays of radioactive materials.

When light is transmitted through matter, part of the light is scattered in random directions. A small part of the scattered light has frequencies removed from the frequency of the incident beam by...

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 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....

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...

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...

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...

An instrument that spectrally analyzes the flux reflected from a material. The reflected flux may be total, diffuse or specular. Often the instrument measures the reflectance factor instead of the...

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

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 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...

The steady state of temperature exhibited by a material that has absorbed and emitted radiation equally.

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...

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.

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

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...

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...

The characteristics of a material that determine its tendency to flow.

Rhodamine refers to a family of fluorescent organic dyes that are widely used in various fields, including biology, chemistry, medicine, and materials science. These dyes are known for their bright...

The formation of a block by attaching optical elements to a plate with a ring of pitch or other thermoplastic material.

Rockwell hardness (Rc) refers to a method for measuring the hardness of a material, primarily metals, using an indentation test. It is named after the Rockwell scale, which was developed by Stanley...