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