Prof Peter Norreys FInstP;

Abstract:

The time-integrated x-ray emission from a hot, dense iron plasma has been recorded. The iron plasma was created when a target with a 1000-Å-thick iron layer buried beneath 1000 Å of plastic was irradiated by a 300 fs pulse of 249 nm laser light at an intensity of approximately 1017 W cm-2. Two models have been used to construct a synthetic x-ray spectrum. The first employs detailed, spectroscopically accurate atomic data and the second uses a local thermodynamic equilibrium opacity model. The detailed model shows fairly good agreement with experiment whereas the opacity model only shows agreement in the gross features. © 1996 American Institute of Physics.

Abstract:

Evidence of high gain pumped by recombination has been observed in the 5g-4f transition at 11.1 nm in sodiumlike copper ions with use of a 20-J 2-ps Nd:glass laser system. The time- and space-integrated gain coefficient was 8.8 ± 1.4 cm-1, indicating a single-transit amplification of ∼60 times. This experiment has shown that 2 ps is the optimum pulse duration to drive the sodiumlike copper recombination x-ray lasing at 11.1 nm. © 1996 Optical Society of America.

Abstract:

We report a study of the effect of prepulses on XUV lasing of Ne-like germanium for an irradiation geometry where ≈20 mm long germanium slab targets were irradiated at ≈1.6 × 1013 W cm-2 using ≈0.7 ns (1.06 μm) pulses from the VULCAN glass laser. Prepulses were generated at fractional power levels of ≈2 × 10-4 (low) and ≈2 × 10-2 (high) and arrived on target 5 and 3.2 ns respectively in advance of the main heating pulse. For both the low and high prepulses the output of the 3p-3s, J=0-1, line at 19.6 nm was enhanced such that the peak radiant density (J/st) for this line became greater than that for the normally stronger J=2-1 lines at 23.2 and 23.6 nm. The 7=0-1 line, whose FWHM duration was reduced from ≈450 ps to ≈100 ps, delivered ≈6X more power (W) than the average for the combined J=2-1 lines, whose FWHM duration was ≈500 ps for both levels of prepulse. The higher prepulse was more effective, yielding ≈2X more radiant density and ≈7X more power on both the J=0-1 and J=2-1 transitions compared to the low prepulse case. The most dramatic observation overall was the ≈40X increase of power in the J=0-1 line for the high prepulse (≈2%) case compared with the zero prepulse case. These observations, coupled with measurements of beam divergence and beam deviation through refractive bending, as well as general agreement with modelling, lead us to conclude that, for germanium, the main influence of the prepulse is (a) to increase the energy absorbed from the main pulse, (b) to increase the volume of the gain zone and (c) to relax the plasma density gradients, particularly in the J=0-1 gain zone.