J. Phys. Colloques
Volume 47, Numéro C6, Octobre 1986International Colloquium on X-ray Lasers / Colloque International sur les Lasers Rayons X
|Page(s)||C6-151 - C6-157|
J. Phys. Colloques 47 (1986) C6-151-C6-157
RECOMBINATION AND PHOTO-PUMPING MECHANISMS FOR PRODUCING GAIN ON HYDROGEN-LIKE BALMER ALPHA LINESG.J. TALLENTS1, 2
1 Laser Physics Laboratory, Department of Engineering Physics, Research School of Physical Sciences, Australian National University, Canberra A.C.T., Australia
2 Presently at JET Joint Undertaking, GB-Abingdon, ml4 3EA, Great-Britain
Two of the most promising classes of schemes for X-ray laser action are the recombination approach, in which population inversions are produced by the decay cascade following electron recombination into high-lying quantum states of a recombining ion, and the photo-pumping approach, in which population inversions are produced by direct pumping of the upper quantum state by photo-excitation from the ground state. In this paper, the recombination and photo-pumping approaches for producing x-ray lasing on the hydrogen-like Balmer alpha line are compared and the effects of the hydrogen-like fine structure on the plasma and other conditions required to achieve Balmer alpha gain are examined. For electron densities Ne ≤ 1012 Z7 cm -3 (where Z is the atomic number of the hydrogen-like ion), it is shown that Balmer alpha gain can be much more difficult to produce than is predicted by simple calculations assuming all sub-levels are populated statistically. It is shown, for example, that Balmer alpha gain produced by 1s-3p photo-pumping becomes impossible for electron densities Ne ≤ 1010 Z7 cm-3 because the 2s1/2 sub-level becomes metastable.