Diagnostics of anisotropic hot electron velocity distribution using x-ray polarization spectroscopy

X-ray polarization spectroscopy is a useful diagnostic tool for measuring the velocity distribution of electrons inside plasma. A new polarization measurement was performed at relativistic laser intensity using a laser pulse (10 J in ∼1 ps) from Alisé facility at CEA/CESTA. Chlorinated triple-layer targets were irradiated, and polarization degrees of C1-Heα line were measured. Obtained polarization degrees are negative in shallow region from the target surface and positive in deep region. This result is qualitatively consistent with the experimental results at non-relativistic intensity. Moreover, de-polarizations due to isotropic excitation and elastic collision, which were predicted by a model calculation and a time-dependent atomic kinetic code, were observed.