SPECTROSCOPIC CHARACTERIZATION OF PREPULSED X-RAY LASER PLASMAS

Through the use of time-integrated space-resolved keV spectroscopy, we investigate line plasmas showing gain in Ne-like nickel, copper, and zinc for irradiation using the prepulse technique. The experiments wer e conducted at 1.06 mu m with the prepulse to main pulse intensity con trast ranging from 10(-6) to 10(-2). The effect of the prepulses on th e plasma conditions is inferred through spectroscopic line ratio diagn ostics for the electron temperature, the Ne-like ground-state density, and the lateral size of the Ne-like region. It is observed that neith er the value of the electronic temperature nor its spatially resolved profile along the linear focus axis varies significantly with the prep ulse level, contrary to the lateral width and the density of the Ne-li ke region in the plasma, which are seen to increase. These results exp lain, at least in part, why prepulsed x-ray lasers show such high gain and brightness.