Partial coherence in diffractive X-ray imaging: past experience as prologue for biomolecular structure determination using XFEL sources

by Harry M. Quiney (School of Physics. University of Melbourne, Australia)

Friday 3 Feb 2012, 10:30 → 12:00 Europe/Berlin

3.11 (AER19)

Coherent diffractive imaging (CDI) using electrons or X-rays has been developed over the past decade to determine structures of nanoscale objects. Whether applied to isolated objects or incorporated within ptychographic procedures to determine the structures of extended objects, the success of conventional CDI procedures depends heavily on the assumption that the scattered radiation can be modelled as a fully coherent wavefield. We will show in this presentation that the explicit incorporation of partial spatial and temporal coherence within diffractive imaging algorithms can dramatically improve image reconstruction quality. Examples will be given in which reconstructions from experimental data are achieved in the presence of significant levels of partial spatial and temporal coherence. The approach is sufficiently general that diffraction-limited image reconstruction is possible using the discrete spectral distributions produced by laser-driven high-harmonic generation sources or the continuous broadband distribution of an undulator harmonic at a third-generation synchrotron. The extreme interaction conditions that prevail in few-femtosecond XFEL scattering experiments inevitably drive a complex sequence of electrodynamical processes in nanoscale electronic targets, such as isolated molecules or nanocrystals. Even if the interaction is short enough that one may neglect the effects of nuclear motion in the encounter between the pulse and the target, the time-dependent scattering properties of such systems may impart the characteristic signature of partial-coherence on diffraction experiments on such systems. We will discuss how the methods that have already been developed for partially-coherent X-ray diffractive imaging using synchrotron sources serve as a prologue to realize current proposals to determine molecular structures using XFEL sources. It will also be shown that the electrodynamical information concerning these complex damage processes is transferable between systems and may be determined by calibration experiments on systems of known molecular structure.