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Numerical Study on Population Inversion and Lasing Conditions in an Optically Thick Recombining Helium Plasma
Author(s) -
Akatsuka H.,
Suzuki M.
Publication year - 1994
Publication title -
contributions to plasma physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.531
H-Index - 47
eISSN - 1521-3986
pISSN - 0863-1042
DOI - 10.1002/ctpp.2150340403
Subject(s) - population inversion , lasing threshold , helium , plasma , atomic physics , materials science , population , laser , computational physics , physics , optics , nuclear physics , demography , sociology
Lasing conditions for He I in a cold recombining helium plasma are numerically discussed including optical thicknesses. A collisional radiative model is used to calculate population densities. We discuss the effect of self absorptions by the background residual gas on the lasing conditions quantitatively. The optical thickness is essential in the calculation and affects the population inversions between level pairs of the singlet state drastically, while those of the triplet state are not affected very much. In the optically thin plasma, the laser lower levels of the singlet state depopulate mainly through radiative transitions. On the other hand, they depopulate mainly through electron collisional deexcitations in the optically thick plasma. Results of the calculations are verified by the spectroscopic observations of an arc‐heated magnetically trapped expanding plasma jet generator which we developed. The requirement for the background pressure in which the lasing is possible is discussed quantitatively.