Calculations of properties of X-ray laser beams. Comparisons with experiments on polarization

摘要

The properties of X-ray laser beams can be quantitatively specified by the Maxwell-Bloch coupled equations. In this paper we consider the polarization properties. The level degeneracies are explicitly taken into account. The intensity evolution of each polarization state of a radiation propagating in a plasma can then be obtained. Our calculations are performed for the Ge~(22+) ion using a post-processor coupled to the code EHYBRID (Pert 1980). For the J=0-J=1 line, we find that the anisotropic radiation trapping due to the ion-velocity gradient in the transverse direction (Kawachi et al 1995) is not efficient enough to produce a polarized single-pass output. The same conclusion is valid when considering the effect of a possible directed beam of hot electrons (Inal et al 1998). However, when an incident linearly-(Rus et al 1995) or circularly-polarized beam corresponding to a lasing line is injected in the plasma, it can be amplified in the plasma without significant de-polarization.