Optimizing 9-25 keV point projection 2D backlighters

The conversion efficiency of zinc He$_{\mathrm{\alpha }}$ backlighter and silver k$_{\mathrm{\alpha }}$ sources have been studied on the OMEGA laser. A common platform was used to evaluate the conversion efficiency from Zn foils with and without a 2.8 ns prepulse and from low density zinc foams containing varying quantities of zinc relative to low Z foam constituents. The common platform consisted of a 2 mm diameter by 2 mm long tube that was either filled with a low density foam or had two foils glued on the ends of an empty tube. The foam targets, which underwent volume ionization, exhibited more uniform radial emission above 1 keV than the foil targets. The thinnest Zn exploding foil targets stagnated in the middle of the tube producing a temporally longer He$_{\mathrm{\alpha }}$ emission than the other targets. The highest overall conversion efficiency came from a foil target driven with a 2.8 ns prepulse. Initial results from silver k$_{\mathrm{\alpha }}$ sources will also be presented.