The trapping of A1(XII) and (XIII) resonance lines in a laser-heated plasma

Abstract

Effects of radiative trapping and quenching processes that may be important on a time scale of tens of picoseconds are examined in connection with the escape of A1(XII) and (XIII) resonance-line photons from a laser-heated aluminum plasma. For the A1(XII) line, radiative trapping by itself would introduce significant delays on this time scale. However, collisional ionization from the excited state is more important and dominates the transfer of this line. Unless the effective optical depth is reduced by rapid internal motions, the time dependence of the A1(XII) line will reflect the source distribution near the surface, rather than the state of the plasma in the interior. For the A1(XIII) line, the delay due to radiative trapping is smaller and collisional ionization is competitive, but does not completely dominate.