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Spatial position of prepulse induced J=0-->1, 3p-3s lasing in low-Z neonlike ions.

We report a spatially resolved investigation of lasing on the 3{ital p} {sup 1}{ital S}{sub 0}--3{ital s} {sup 1}{ital P}{sub 1} transition in neonlike ions ranging from titanium ({ital Z}=22) to germanium ({ital Z}=32). Slab targets were irradiated by the Asterix IV iodine laser at an intensity of about 2.0{times}10{sup 13} W/cm{sup {minus}2} with a prepulse 5.23 ns before the main pulse. The lasing position was measured as a function of the prepulse energy and the atomic number. It was found that with higher {ital Z}, the lasing occurs closer to the target surface and a larger prepulse brings the lasing farther away from the target. A 15% prepulse was found to be favorable for low-{ital Z} elements (such as titanium), while a 1.5% prepulse was found to be favorable for elements with {ital Z} higher than 26. A simple model taking into account the self-similar expansion of the plasma produced by the prepulse was found to agree qualitatively with the experimental results.