Plasma and X-UV source characteristics for Al targets heated by 40 ns Nd-laser pulses

The total laser energy (3-32 J), temporal history (40 ns full width at half maximum) and focal energy distribution (3 x 10(13) W/cm(2) peak, 1.5 x 10(13) W/cm(2) average) for lambda = 1.06 mum Nd:glass laser interactions with planar Al targets were measured. Laser-produced plasma emissions within the 1-3 keV x-ray range were recorded, with limited measurements in the 10-1000 eV range. Primary emphasis was given to obtaining the dependence of kilovolt x-ray emission on irradiance (varied by altering the energy on target or the lens-target spacing). A maximum efficiency for the conversion of incident laser energy to radiation above 1.5 keV was 0.25% into 2 pi sr. Integrated x-ray energy radiated over this range of photon energy was found to increase as the 3.2 power of laser energy at best focus. X-ray emission decreased when a prepulse preceded the main pulse by a controlled amount exceeding 0.2 mus but <5 mus, with a minimum emission at 0.5 mus separation. Plasma temperatures were estimated from x-ray line ratios and continuum slopes: a value near 230 eV was obtained from free-bound continuum slope for 3 x 10(13) W/cm(2) peak irradiance. Temperatures decreased at lower irradiances, as inferred from x-ray line ratios.