Efficient J=0-1 soft-X-ray lasing in neon-like ions at pump powers below 250 GW

2 . By using a 0.7% prepulse that precedes the main pulse by 5 ns and applying a total pump energy of 100 J or less, the J=0-1 lasing is at least one order of magnitude higher than the non-lasing background. For the 32.6-nm line of Ti, the 25.5-nm line of Fe, and the 23.1-nm line of Ni, gain coefficients of (±) 4.20.4cm^-1, (±) 3.90.3cm^-1, and (±) 3.60.6cm^-1, respectively, were measured for 2.4-cm-long curved targets, resulting in gain–length products of ∼10. Angle-resolved spectra indicate a beam divergence of 3 mrad (FWHM), typically. The space-resolved spectra show that the J=0-1 lasing lines are emitted from an approximately 60-μm-wide (FWHM) plasma region, whereas the nearby continuum emission is produced in a considerably broader plasma region of ∼250 μm. Lasing at 25.5 nm in neon-like iron was observed at a pump power as low as 180 GW (∼9 TW/cm²), with, however, considerable shot-to-shot scatter in the absolute laser output. Received: 5 September 1997/Revised version: 10 November 1997