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The first subnanosecond, time-resolved, and spatially localized recombination continuum measurements are reported. The possibility of a non-Maxwellian velocity distribution is deduced from the shape of the recombination spectrum that is observed during the time when the plasma is being created by the laser. The cooling rate of the plasma is derived for later times, when no laser heating is present. [ABSTRACT FROM AUTHOR]

We have observed enhanced emission of the O VIII Hα line at 121 eV from a recombining plasma produced by laser heating of a thin Formvar foil with two opposed cylindrically focused (0.3×1.4 cm) 5-TW laser beams. The time-dependent intensity of the Hα line increases by nearly an order of magnitude as the plasma length is increased from 0.27 to 1.27 cm. This increase in intensity is greater than that expected from a medium exhibiting no gain. A comparison of the measured time history of the emission with that of non-local thermodynamic equilibrium time-dependent calculations suggests that a small-signal gain ∼0.5 cm-1 is obtained. [ABSTRACT FROM AUTHOR]