Advanced x-ray diagnostics based on an observation of high-energy Rydberg transitions from autoionizing levels in dense laser-produced plasmas

Abstract

The application of x-ray spectroscopy methods enabled a space-resolved observation of the high-energy Rydberg satellite series ${1s2lnl}^{\ensuremath{'}}\ensuremath{\rightarrow}{1s}^{2}2l+h\ensuremath{\nu}$ and the ${\mathrm{Ly}}_{\ensuremath{\beta}}$ satellites ${2l3l}^{\ensuremath{'}}\ensuremath{\rightarrow}1s2l+h\ensuremath{\nu}$ in dense laser-produced plasmas. Ab initio atomic structure calculations including relativistic and QED effects show excellent agreement with the precise wavelengths measurements. Satellite transitions with $n>3$ split into three distinct groups. For $n>5,$ the transitions are found to merge with the ${\mathrm{Ly}}_{\ensuremath{\beta}}$ satellite transitions ${2l3l}^{\ensuremath{'}}\ensuremath{\rightarrow}1s2l+h\ensuremath{\nu}$ and the series limits approach the ${\mathrm{Ly}}_{\ensuremath{\beta}}$ line. This leads to emission on the red and even on the blue wing of the ${\mathrm{Ly}}_{\ensuremath{\beta}}$ line. Spatially and spectrally resolved intensity distribution discovered strong spatial restrictions of the Rydberg satellite intensities near the target surface. On the contrary, all resonance lines show strong emissions up to 10-mm distance from the target and large optical thickness. This enabled us to develop essentially opacity-free and spatially localized temperature diagnostics based on Rydberg satellite emission. Total x-ray emission spectra are established with the help of the MARIA suite of kinetic codes. The derived properties of the spectral distribution make the high-energy Rydberg satellites of general interest for the wide class of dense plasma experiments.