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Lowering of the Populations of Excited Hydrogen and Helium Atoms in Plasmas Irradiated by a Laser Beam
Author(s) -
Drawin H. W.,
Emard F.,
Dubreuil B.,
Chapelle J.
Publication year - 1974
Publication title -
beiträge aus der plasmaphysik
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.531
H-Index - 47
eISSN - 1521-3986
pISSN - 0005-8025
DOI - 10.1002/ctpp.19740140402
Subject(s) - photoionization , atomic physics , excited state , plasma , helium , laser , argon , irradiation , hydrogen , ion , radiation , chemistry , ionization , physics , optics , nuclear physics , organic chemistry
The populations of excited hydrogen and helium atoms in non‐L.T.E. plasmas have been calculated for two different physical situations, namely (i) no external radiation field present, and (ii) strong superposed radiation originating from a CO 2 , Ruby or Argon Ion Laser. The radiation field intervenes in the collisional‐radiative model via two new terms: Photoionization and stimulated recombination induced by the Laser radiation field. The solutions of the rate equations yield a lowering of the populations when a plasma is irradiated by a Laser beam. The lowering is different for cold recombining and hot diffusion‐dominated plasmas. At high radiation densities a saturation effect occurs, since the photoionization rate becomes equal to the rate of stimulated recombination. Measurements of the populations of excited H and He atoms in a glow discharge irradiated by a CO 2 Laser beam of power density 10 5 W/cm 2 are in broad agreement with the theoretical predictions.