High-Ti-concentration foams as laser-driven x-ray sources*

Metals between Ti and Ge are used for bright x-ray sources in the 4-10 keV range when irradiated by energetic nanosecond lasers. To maximize their laser-to-x-ray conversion efficiency (CE), lower density is preferred, achieved usually with pre-exploded thin foils or very-low-density foams (\textless 10 mg/cm$^{3})$. We present recent experimental results using novel foams of high Ti concentration. Previous foams were doped with less than 5 at{\%} of Ti. We manufactured two new types of foams with density $\sim$ 5 mg/cm$^{3}$ and Ti concentrations 20 and 33 at{\%}. They have been tested as x-ray sources in two laser facilities, OMEGA (USA) and GEKKO XII (Japan). CEs \textgreater 5{\%} are measured, significantly higher than previous achievements with the lower-concentration foams. We describe laser-heating dynamics simulation results and comparisons to time-resolved measurements, indicating strong differences between the several foams used.