Interaction of photons with ionized matter

Article By:

Phaneuf, Ronald A. Department of Physics, University of Nevada, Reno, Nevada.

Last reviewed:2006

DOI:https://doi.org/10.1036/1097-8542.YB061320

Most of the known matter in the universe exists in ionized (charged) form, and nearly all knowledge about it is carried to us by light (photons). Important to astrophysicists is an understanding of the origin of those photons and their encounters during journeys taking light-years to reach our telescopes. Interactions of photons with ionized matter are also critical in diagnosing and understanding the properties of hot ionized gases (plasmas) that are encountered in research to harness nuclear fusion, the energy source of the Sun. As an atom successively loses electrons and becomes highly ionized, it is left with electrons that are more strongly attracted to the nucleus than those that have been stripped away, and transitions between electronic energy levels shift to shorter wavelengths. Correspondingly, the spectral fingerprints of multiply charged ions shift from the visible to the extreme ultraviolet and x-ray regions of the electromagnetic spectrum.

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