Analysis of x-ray polarization to determine the three-dimensionally anisotropic velocity distributions of hot electrons in plasma produced by ultrahigh intensity lasers.

A new polarization spectroscopy model has been developed to analyze energetic electrons distributed in a three-dimensional phase space. This model calculates the polarization degrees for a given line of sight. Time-dependent polarization degrees of Healpha line emitted from heliumlike chlorine ions was obtained for two different lines of sight by using three-dimensional electron velocity distributions provided with two-dimensional particle-in-cell simulations. These results demonstrate that the polarization degrees are sensitively dependent on the profile of the electron velocity distributions which are affected by the polarization of the laser pulse.