reemit

Reemit is a verb meaning to emit again or to reemit energy that was previously emitted or absorbed. In physics and related disciplines, reemission refers to the production of radiation by a system after it has absorbed energy, often through transitions between energy levels. Reemission is distinguished from mere reflection in that the emitted radiation originates from excited states within the material rather than being a direct copy of the incoming wave.

In optics and photophysics, absorbed photons can be followed by fluorescence or phosphorescence, where the material reemits light at longer wavelengths, sometimes with a time delay. Reemission also occurs when photons are absorbed by astronomical dust grains and reemitted as infrared radiation, contributing to the observed spectral energy distribution of stars and galaxies and playing a key role in the energy balance of the interstellar medium.

In broadcasting and media contexts, reemit is used informally to mean re-air or disseminate a program or signal again, such as reemitting a radio show or podcast episode.

In scientific modeling, reemission must be accounted for in radiative transfer, since absorbed energy can be reemitted multiple times within a medium, altering spectra and temperature distributions. Emissivity, absorption coefficients, and Kirchhoff's law govern these processes.

See also: fluorescence, phosphorescence, radiative transfer, secondary emission, infrared astronomy.