The study of shock compressed condensed matter by use of advanced light sources

The use of x-rays to interrogate condensed matter under shock compression has a long history.  Light sources, including high-power lasers, have been used since the mid 1980’s to create sub-nanosecond flashes of quasi monochromatic x-rays that can be diffracted from materials synchronously compressed by laser ablation.  More recently advanced light sources, such as synchrotrons and hard x-ray free-electron-lasers, have been used to create the ultra-short x-ray probes. The underlying motivation is clear: via diffraction x-rays can yield information on what is happening at the lattice level.  Not only does this allow new shock-induced phases to be determined in situ, but it can also provide unique information on the plastic deformation processes at play, even to the degree that individual types of defects and slip-systems involved can be identified.  Such measurements give an insight into the fundamental physics that no macroscopic or recovery measurement can provide, and give a direct link to predictions of molecular dynamics calculations.  The quality of the diffraction patterns obtained is spectacular, and with the pulse lengths of FELs well below 100-fsec, single-shot data can be obtained on a timescale faster than the period of the most energetic phonons in the system.  However, the elastic scattering that comprises diffraction is not the only means of diagnosis that such sources provide, and there is a burgeoning interest in using both inelastic scattering and absorption techniques to probe other aspects of the system, such as the phonon spectrum under compression, or the electronic density of states. In this talk I will outline some of the recent advances that have been made in this area, which include, but are not limited to, a demonstration of the ultimate strength of crystalline matter under compression, an observation under shock conditions of one of the most complex phases that a single element can possess, and the identification of specific deformation mechanisms and pathways that operate in common fcc and bcc metals.  Future developments in the x-ray sources themselves, such as increased photon energy and reduced bandwidth, alongside the placing of novel shock drivers alongside them, herald an increase in data acquisition rate and the extent of the phase diagram of compressed matter that can be interrogated.