Soft-x-ray lasing at 32.6nm in Ne-like Ti ions driven by 40 J of energy from two 650-ps laser pulses

Using only 40 J of drive energy in a 650-ps main pulse we demonstrated lasing on the J=0-->1, 3p-->3s transition in neonlike titanium at 32.6 nm. This is an order of magnitude smaller drive energy than has been used previously to drive low-Z neonlike x-ray lasers. We present a series of experiments using titanium slab targets which study the threshold for lasing in neonlike titanium when the 1.8-cm-long targets are illuminated by a low-intensity prepulse 5 ns before the main optical drive pulse of the 1.05-mu m Xingguang Nd-glass laser. For a 1% prepulse, the energy threshold is measured to be 40 J, which contrasts with 110 J for a 9% prepulse. In both cases, the 32.6-nm Ti lasing line peaks 5 mrad off-axis with divergences of 4 and 5 mrad for the 1% and 9% prepulse cases, respectively.