Studies of population inversion and gains for xuv laser development in a recombining plasma column

An experimental study is presented of population inversions and gains in CO2 laser produced plasmas in a number of different solid and gas targets, with and without the presence of a magnetic field. Population inversions and gains were measured in hydrogenic carbon, CVI, and in the Li-like sequence CIV, OVI, FVII, and NeVIII. The Li-like species were easily produced in gas targets and, in general, 4d-3d population inversions were seen to increase with a combination of higher target pressure and the presence of an external magnetic field. Ratios of the 4d-3d sublevel populations ranged up to approx.10, for OVI. Inversions in CIV and FVII, in cases where solid targets were used, were less sensitive to the presence of the magnetic field. Gains in the CVI 182.17 A (3-2) line were measured using solid carbon targets, and increased in the presence of a magnetic field. The effect of placing aluminum blades near the target, for plasma cooling and faster recombination, was inconclusive. In general, gains determined by measuring an on-axis enhancement of the 182.17 A line were consistent with absolute measurements of CVI excitation-level populations. Gains of 2-4 cm-1 were measured. Axially oriented carbon-fiber targets were irradiated by the CO2 laser, and it was found that population inversions and gain resulted only when there was no magnetic field present