C vi Lyman line profiles from 10-ps KrF-laser-produced plasmas

Plasmas with densities \ensuremath{\lesssim}${10}^{22}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ and electron temperatures ${\mathit{T}}_{\mathit{e}}$\ensuremath{\lesssim}200 eV were produced near solid graphite targets that were laser irradiated at \ensuremath{\sim}${10}^{15}$ W/${\mathrm{cm}}^{2}$, with a \ensuremath{\sim}${10}^{11}$ W/${\mathrm{cm}}^{2}$ prepulse from amplified spontaneous emission. Photographic spectra taken nearly side-on within \ensuremath{\lesssim}0.1 mm from the target surface show strong H-like lines corresponding to n=2,3, and 4 to n=1 transitions and weaker He-like lines, with full width at half maximum widths \ensuremath{\lesssim}4 eV. The Lyman-\ensuremath{\alpha} line is optically thick. A five-layer model with high-electron-density and electron-temperature core layers and less dense and cooler outer layers was used for simulation. Central layers with high ${\mathit{T}}_{\mathit{e}}$ contribute most of the emission while outside cooler layers cause an absorption dip in the central part of the Lyman-\ensuremath{\alpha} line. Asymmetrical self-reversal is interpreted by radial expansion. A plasma-induced line shift was evident in some of the experimental line profiles, especially for the asymmetrical and strongly shifted Lyman-\ensuremath{\gamma} line of C vi ions. Time-dependent rate equations were solved for checking the assumed local-thermodynamic-equilibrium condition for plasmas with adiabatic expansion cooling.