X-ray spectra from highly ionized dense plasmas produced by ultrashort laser pulses

Hydrogen-like and helium-like X-ray spectra (between 7.1 and 8.2 Angstrom, i.e., 1500 to 1750 eV, respectively) from solid aluminium targets irradiated with high intensity (up to 10(17) W/cm(2)) subpicosecond (0.7 ps) laser pulses have been measured. The spectra show that the resonance lines are very broad and very asymmetric. Evidence for a Doppler-shifted reabsorption of the resonance line emission has been found. The spectra have been simulated by a computer code for the calculation of spectral-line intensities and linewidths. Electron densities exceeding the critical density have been estimated for different laser intensities by comparing the observed and simulated intensity ratio of different dielectronic satellite lines. From the X-ray spectra generated by p- and s-polarized radiation at different laser intensities, the thresholds for the formation of hydrogen-like and helium-like ions have been determined.