The influence of prepulse level on the 3p-3s XUV laser output from Ne-like ions of Zn, Cu and Ni

We have studied the effect of prepulses in enhancing the efficiency of generating ASE beams in soft X-ray laser plasma amplifiers based on pumping Ne-like ions. Slab targets were irradiated with a weak prepulse followed by a main plasma heating pulse of nanosecond duration. Time-integrated; time and spectrally resolved and time and angularly resolved lasing emissions on the 3p-3s (J = 0-1) XUV lasing lines of Ne-like Ni, Cu and Zn at wavelengths 232 Å, 221 Å and 212 Å respectively have been monitored. Measurements were made for pre-pulse/main-pulse intensity ratios from 10^-5-10^-1 and for pump delay times of 2 ns and 4.5 ns. Zinc is shown to exhibit a peak in output intensity at ∼ 2 × 10^-3 pre-pulse fraction for a 4.5 ns pump delay, with a main pulse pump intensity of ∼ 1.3 × 10¹³ Wcm^-2 on a 20 mm target. The Zn lasing emission had a duration of ∼ 240 ps and this was insensitive to prepulse fraction. The J = 0-1 XUV laser output for nickel and copper increased monotonically with prepulse fraction, with copper targets showing least sensitivity to either prepulse level or prepulse to main pulse delay. Under the conditions of the study, the pre-pulse level was observed to have no significant influence on the output intensity of the 3p-3s (J = 2-1) lines of any of the elements investigated.