Recent Progress on Laser-Driven 10.3 keV X-Ray Sources

Underdense, laser-driven targets have been shown to be efficient converters of laser light into X rays. We report on recent experiments at the OMEGA laser carried out in order to optimize the X-ray yield from Ge-doped SiO$_{2}$ aerogel targets. We have varied the aerogel-target density from 3.6 to 6.5 mg/cm$^{3}$ keeping the fraction of Ge atoms fixed at 20{\%}. Laser intensity on target varied from 2$\times $10$^{15}$ -- 7$\times $10$^{16}$ W/cm$^{2}$ and laser-pulse lengths from 1 to 6 ns; the total energy delivered to the targets is nearly 20 kJ. The X-ray output from the targets has been measured with absolutely calibrated crystal spectrometers and photo-conductive devices (PCDs) and X-ray diodes, which also provide a temporal history of the X-ray output. Target performance in the 10.3 keV X-ray band is presented as a function of these parameters. We find $\approx $1{\%} of the laser energy is converted into X rays in the 9--15 keV band. Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. W-7405ENG-48. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the U.S. Department of Energy under Contract DE-AC04-94AL8500.