Detailed study of the effect of a short prepulse on soft X-ray spectra generated by a high-intensity KrF* laser pulse

The effect of a short prepulse (0.5 ps) on soft X-ray spectra from a plasma generated by a high intensity KrF* laser pulse (main pulse: 0.5 ps, intensity Imain=5.3×1015 W/cm2) on flat targets of Al and Cu has been studied in detail. The spectra have been measured as a function of the pulse separation Δt between the two pulses and the prepulse intensity Ipre. It was found that both the overall emission and the line emission increased with Δt (at constant Ipre) and with Ipre (at constant Δt). In particular, lines in the shorter wavelength region had higher intensity. The influence of the prepulse on the line emission of specific transitions in the Al spectra was investigated systematicly. An explanation for the observed effects is given.

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