Extended x-ray absorption fine structure measurements of laser shocks in Ti and V and phase transformation in Ti

A laser-source-based extended x-ray absorption fine structure (EXAFS) measurement has been used to study the properties of laser-shocked metals on a nanosecond time scale. The ability of measuring shock-induced temperatures of the order of 0.1 eV is essentially unique to EXAFS. EXAFS measurement of vanadium shocked to ∼0.5 Mbar with a 3 ns laser pulse yields a compression and temperature in good agreement with hydrodynamic simulations and with shock-speed measurements. In laser-shocked titanium at the same pressure, the EXAFS modulation damping is much higher than warranted by the increase in temperature. This is explained by the α-Ti to ω-Ti phase transformation known to occur around ∼0.1 Mbar in the longer (μs) shocks obtained in gas-gun experiments. In the ω-Ti phase, the disparate neighbor distances cause a beating of the modulation frequencies and thus an increased damping. These results demonstrate that EXAFS measurements can be used for the study of nanosecond-scale shocks and phase transformation in metals.