Studies of the Structure of Matter with Photons from an X-ray Free-Electron Laser

Abstract

X-ray free-electron lasers offer the potential for fourth-generation ultra-high peak power and coherence X-ray beams in the hard X-ray (8 keV) spectral range. A critical review of three areas of potential application of such sources is presented. Owing to the enormous electric field strength at the focus of such beams, it is shown that matter would very rapidly form a plasma for focal spots of submicrometer dimensions. Thus, hologram formation would only be feasible for crystalline samples with dimensions of a few micrometers or greater. A new version of X-ray holography using interference between a sample and a reference two-dimensional crystal is proposed. Because of the very high peak intensity of the free-electron-laser pulses, a natural application is to time-resolved multibunch ;dynamic X-ray scattering' measurements. It is shown that this could provide information on dynamical processes in condensed matter complementary to that obtained using slow neutron beams. Finally, optical laser-induced pump-probe-type experiments are reviewed. There is the potential for extending the study of the charge distribution of electronic excited states to those with lifetimes in the submillisecond time range.

Ultrafast time-resolved crystallography

“…The desirability of even faster time-resolved crystallographic experiments is thus opened up 25 for which novel experimental approaches will be necessary, either through extension of the present pumpprobe approach, or through radically new approaches 26,27 . Ultrafast time-resolved crystallography provides an approach to mechanism at the structural level through 'no trapping' of intermediates, in contrast to the more conventional approaches of 'chemical trapping' and 'physical trapping' at cryogenic temperatures [28][29][30] .…”

X-Ray Free-Electron Lasers for the Structure and Dynamics of Macromolecules

“…Phase Retrieval.-Noncrystalline objects produce oversampled diffraction patterns from which phases can be directly recovered in an iterative process [16] where two constraints are sequentially enforced. The first constraint is that the Fourier amplitudes have to be consistent with the collected data.…”

“…The support was handled by a Shrinkwrap algorithm [19] with the constraint to have a specific area. The result was refined with 1000 iterations of the error reduction (ER) algorithm [16]. conclusion is based on an analysis method described in [7].…”

Radiation damage in protein crystallography at X-ray free-electron lasers

“…duration in the sample can lead to the formation of hot plasma (Chapman et al, 2014). Interestingly, the interaction between the very high electric field strengths ($6 Â 10 5 V Å À1 ) resulting from an extreme number of photons per atom (>10 9 photons Å À2 ) and atoms in the sample was predicted to cause plasma formation in less than 1 fs owing to an 'inverse bremsstrahlung' effect (Doniach, 1996).…”