X-ray polarization spectroscopy for measurement of anisotropy of hot electrons generated with ultraintense laser pulse

Polarization spectroscopy is a useful diagnostic method to measure directly the anisotropy of hot electron velocity distribution function inside ultrahigh intense laser produced plasmas. Polarization of a Cl – He α line (2.79 keV ) from double-layer targets, which consist of polystyrene and chlorinated polystyrene, was observed with a toroidally curved crystal spectrograph. It was found that the line from the target surface is polarized more parallel to the surface, whereas that from a deeper region is more perpendicular to it. The polarization of emitted x rays corresponds to the shape of velocity distribution function of hot electrons. The anisotropic shape of hot electron velocity distribution function depending on depth of a target was clarified for the first time using this diagnostic method.