RESUMEN
In situ white light Laue diffraction has been successfully used to interrogate the structure of single crystal materials undergoing rapid (nanosecond) dynamic compression up to megabar pressures. However, information on strain state accessible via this technique is limited, reducing its applicability for a range of applications. We present an extension to the existing Laue diffraction platform in which we record the photon energy of a subset of diffraction peaks. This allows for a measurement of the longitudinal and transverse strains in situ during compression. Consequently, we demonstrate measurement of volumetric compression of the unit cell, in addition to the limited aspect ratio information accessible in conventional white light Laue. We present preliminary results for silicon, where only an elastic strain is observed. VISAR measurements show the presence of a two wave structure and measurements show that material downstream of the second wave does not contribute to the observed diffraction peaks, supporting the idea that this material may be highly disordered, or has undergone large scale rotation.
RESUMEN
Under uniaxial high-stress shock compression it is believed that crystalline materials undergo complex, rapid, micro-structural changes to relieve the large applied shear stresses. Diagnosing the underlying mechanisms involved remains a significant challenge in the field of shock physics, and is critical for furthering our understanding of the fundamental lattice-level physics, and for the validation of multi-scale models of shock compression. Here we employ white-light X-ray Laue diffraction on a nanosecond timescale to make the first in situ observations of the stress relaxation mechanism in a laser-shocked crystal. The measurements were made on single-crystal copper, shocked along the [001] axis to peak stresses of order 50 GPa. The results demonstrate the presence of stress-dependent lattice rotations along specific crystallographic directions. The orientation of the rotations suggests that there is double slip on conjugate systems. In this model, the rotation magnitudes are consistent with defect densities of order 10(12) cm(-2).