EXAFS Measurements of Laser-Generated Shocks with an Imploded Target as a Radiation Source

LLE Review, Volume 94 107 Introduction Recently, great interest has been shown in the study of dynamic material response to shocks of high pressure and high strain rate.1,2 Shocks of up to ~1 Mbar and strain rates of ~107 to 108 s-1 were generated in metals (Al, Cu) by laser irradiation. The laser intensity in those experiments (~1011 W/cm2) was high enough to raise the pressure above the Hugoniot elastic limit (HEL) but low enough for the compressed material to remain solid. Using Bragg and Laue x-ray diffraction, the experiments clearly showed the retention of crystallinity during the passage of the shock. Silicon under these conditions was found to compress elastically, i.e., only in the direction of shock compression. Copper, on the other hand, was found to compress equally in all dimensions, indicating the transition to plastic flow. These differences were explained in terms of the different velocity of dislocation propagation that gives rise to the elastic–plastic transition.