Coherence loss by sample dynamics and heterogeneity in x-ray laser diffraction

In its most common implementations, single particle imaging with x-ray free-electron lasers (XFELs) assumes the perfect coherence of the diffracted x-rays. However, XFEL imaging is destructive and exhibits a reduction of coherence due to sample dynamics (radiation damage). Sample heterogeneity also manifests as effective loss of coherence in averaged data, which is increasingly encountered in the development of 3D XFEL imaging techniques. Here we review coherence loss in XFEL imaging experiments, which has focused primarily on femtosecond electronic dynamics. We present extensions of coherence theory to XFEL crystallography, ion diffusion, the Coulomb explosion of a single particle and to heterogeneity using a spherical model. In each case, we provide illustrative simulations of the effects of coherence loss and discuss when these effects will need to be taken into account. (paper)