Absolute X-Ray Yields from Laser-Irradiated Metal-Doped Low-Density Aerogels

The X-ray yields from laser-irradiated, high-Z-doped, ultra-low-density aerogel plasmas have been measured in the energy range from sub-keV to 13 keV at the 20~kJ OMEGA laser. The targets' X-ray yields have been studied for variation in target size, aerogel density, laser pulse length and intensity. For Ti-doped targets that result in plasmas with electron densities in the range of $\sim $10{\%} of the laser's critical density, one can expect $\sim $2{\%} laser-to-X-ray conversion efficiency (CE) in the 4 - 6 keV energy band; for Zn-doped aerogels, $\sim $1{\%} CE has been measured for 9 keV X rays. For Ge-doped aerogels, one can expect $\sim $0.7{\%} laser-to-X-ray CE for X-rays above 9 keV, and $\sim $40{\%} CE for energies below 3.5 keV. These results for doped-aerogel targets are consistent with other CE measurements made recently at the GEKKO laser for metallic Ti nano-fiber materials, and are also consistent with recent measurements of CEs for Ge-lined cavities, but are below the CEs measured for Ti-lined cavities and below the CEs measured for pre-exploded Ti foils.