Direct visualization of high-pressure phase nucleation and multi-wave kinetics in shocked Silicon using X-ray imaging at LCLS.*

We report on results from a new X-ray imaging diagnostic at the Matter in Extreme Conditions endstation at the Linac Coherent Light source and new insights into the behavior of silicon (Si) under laser-driven shock compression.

The multi-wave response of Si to shock loading has been debated for decades, and a recent study has demonstrated the lack of conventional plasticity using X-ray diffraction (XRD). To elucidate the mechanism of the complex multi-wave shock formation, we have combined XRD and X-ray imaging to visualize the growth of the high-pressure phase in situ. With the high spatial resolution (<600nm) and temporal resolution (<100fs) of our setup, we can resolve the kinetics of Si deformation under shock compression. We show the emergence of the intermediate elastic feature previously reported, and we observe the nucleation and growth of the high-pressure phases. Interestingly, the high-pressure phase grows preferentially in a banding structure that had been predicted by MD simulations but never recorded during a shock before.

With these results, we demonstrate the capability of the new X-ray imaging setup at the LCLS to provide detailed information on the macroscopic and microscopic behavior of materials over the ultrafast (ns) timescales of shock compression.