Measuring preheat in laser-drive aluminum using VISAR

In this paper, we systematically study preheating in laser-direct-drive shocks by using a velocity interferometer system for any reflector (VISAR). Using the VISAR we measured free surface velocity histories of Al samples over time, 10--70 $\mu $m thick, driven directly by a laser at different frequencies (2$\omega$ - 3$\omega )$. Analyzing our experimental results, we concluded that the dominant preheating source was X-ray radiation. We also discussed how preheating affected the material initial density and the measurement of Hugoniot data for high-Z materials (such as Au) using impedance matching. To reduce preheating, we proposed and tested three kinds of targets.