Texture Effects in Inelastic X-Ray Scattering in HED Experiments

It has recently been shown that the intensity of x-ray thermal diffuse scattering (TDS) from shocked solids can be used as a single-shot femtosecond temperature measurement [1]. The procedure uses the classic theory of Warren, based on the Debye approximation. With sufficient azimuthal angular averaging between the Deybe-Scherrer rings (but resolving the scattering angle) the TDS is remarkably insensitive to the texture of the target. However, this will not necessarily be the case for spectrally resolved measurements, where the collection optics dictate that the azimuthal coverage is far smaller. Whilst the full dynamic structure factor, S(k,ω), including all-order multi-phonon scattering, can be constructed for a randomly ordered sample, such a calculation in the presence of texture is more complicated. We concentrate here on the more tractable case of comparing S(k,ω) for textured and random samples within the Warren-based theory when single phonon events dominate (i.e. Debye-Waller factors are less than unity). We further discuss the underlying simple physics of how one moves from the phonon model for the solid, to the standard result as the material enters the warm dense fluid or plasma phase.

[1] J.S. Wark et al., J. Appl. Phys. 137, 155904 (2025).