Abstract
Subpicosecond soft x-ray pulses have applications as x-ray flashlamps for photoionization-pumped x-ray lasers and as sources for time-resolved x-ray scattering experiments. However, the high-intensity laser-produced plasma schemes that use solid targets to keep the x-ray pulse short tend to be very inefficient because of the high reflectivity of the target surface.1 Prepulsed targets are more efficient emitters, but they also tend to emit. more hard x rays, which may be damaging in some applications. We have demonstrated that a plasma created in a pomus medium emits much more efficiently near 1 keV than does a flat target, but it emits few hard x rays. We used a form of porous gold called “gold black”2 as a target. The name arises because this material appears velvety black to the eye. It efficiently absorbed almost all of the incident laser energy- With 100 mJ on target, black gold emitted 1.5 mJ of x rays above 1 keV, for a conversion efficiency of 1.5%. Solid gold, for comparison, provided a conversion efficiency of 0.02%.
© 1993 Optical Society of America
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