Theoretical predictions for the polarization of X-ray laser lines in the presence of a directed beam of hot electrons

The 19.6 nm laser line due to a 3p - 3s, J=0-1 transition in Ne-like Ge ion s was found to be polarized parallel to the target plane with a degree of p olarization of -53 % by Kawachi et al. (1995). They intepret it as a conseq uence of a an unbalanced population of the 3s magnetic sublevels. Kieffer e t al. (1993) have shown that, during plasma heating, some electrons could b e accelerated preferentially in the same direction as the pump laser. In th e present work, we shall show that such anisotropic electrons can give a sm all difference in populations of the 3s sublevels. The 3s level spontaneous emission to the ground level is linearly polarized and can be reabsorbed b y the Ne-like ion ground state which amplifies the population of the 3s lev els, as well as it increases the different sublevel populations. The 3p-3s X-ray laser amplification depending on the 3s level population becomes pola rized but with an opposite sign to the absorbed radiation from the ground l evel.