OBSERVATION OF INTENSE SOFT-X-RAY LASING AT THE J = 0 TO J = 1 TRANSITION IN NEON-LIKE ZINC

We present experimental results from recent studies of soft-x-ray lasing in Ne-like Zn (Z = 30). The lasing plasma was produced by irradiation of slab targets as much as 2 cm long with intensities of approximately 1.4 x 10(13) W cm-2 at lambda = 1.06 mum in pulses of 600 ps (FWHM). Amplification at three 3p-3s transitions was observed. While the J = 2 to J = 1 transitions at 262 and 267 angstrom provided gain coefficients of 2.3 and 2.6 cm-1, respectively, the J = 0 to J = 1 transition at 212 angstrom exhibited a significantly larger gain of 4.9 cm-1 and yielded a much brighter signal. Furthermore, its temporal characteristics were revealed to be unlike those of the J = 2 to J = 1 transitions. The results indicate that the J = 0 to J = 1 line originates from a different plasma region than do the J = 2 to J = 1 lines and that the temporal evolution of the pumping process into its upper lasing level J = 0 differs considerably from that to the J = 2 levels. In addition, the gain and the gain-length product of approximately 10 achieved in this experiment are, to our knowledge, the highest ever reported for a driving laser of similar energy (approximately 450 J).