Observation of Polarization of the Soft X-Ray Laser Line in Neonlike Germanium Ions

Abstract

A 3-cm-long curved Ge slab target was irradiated by 1.053 \ensuremath{\mu}m glass laser light with irradiance of 2.9 \ifmmode\times\else\texttimes\fi{} ${10}^{3}$ W/${\mathrm{cm}}^{2}$. The 19.6 nm laser line due to the $3p\ensuremath{\rightarrow}3s$, $J=0\ensuremath{\rightarrow}1$ transition in Ne-like Ge ions was found to be polarized parallel to the target surface, with a degree of polarization of -53%. This polarization is accounted for by the anisotropy in the radiation trapping of the resonance line in an expanding plasma, which has a velocity gradient in the direction normal to the target surface.