Hanbury Brown and Twiss interferometry at a free-electron laser

We present measurements of second- and higher-order intensity correlation functions (so-called Hanbury Brown and Twiss experiment) performed at the free-electron laser (FEL) FLASH in the non-linear regime of its operation. We demonstrate the high transverse coherence properties of the FEL beam with a degree of transverse coherence of about 80% and degeneracy parameter of the order 10^9 that makes it similar to laser sources. Intensity correlation measurements in spatial and frequency domain gave an estimate of the FEL average pulse duration of 50 fs. Our measurements of the higher-order correlation functions indicate that FEL radiation obeys Gaussian statistics, which is characteristic to chaotic sources.Comment: 19 pages, 6 figures, 1 table, 40 reference

Revealing three-dimensional structure of individual colloidal crystal grain by coherent x-ray diffractive imaging

We present results of a coherent x-ray diffractive imaging experiment performed on a single colloidal crystal grain. The full three-dimensional (3D) reciprocal space map measured by an azimuthal rotational scan contained several orders of Bragg reflections together with the coherent interference signal between them. Applying the iterative phase retrieval approach, the 3D structure of the crystal grain was reconstructed and positions of individual colloidal particles were resolved. As a result, an exact stacking sequence of hexagonal close-packed layers including planar and linear defects were identified.Comment: 8 pages, 5 figure

Solution of the phase problem for coherent scattering from a disordered system of identical particles

While the implementation of single-particle coherent diffractionimaging for non-crystalline particles is complicated by current limitations onphoton flux, hit rate and sample delivery, the concept of many-particle coherentdiffraction imaging offers an alternative way of overcoming these difficulties.In this paper, we present a direct, non-iterative approach for the recovery of thediffraction pattern corresponding to a single particle using coherent x-ray datacollected from a two-dimensional disordered system of identical particles; thisapproach does not require a priori information about the particles and can beapplied to the general case of particles without symmetry. The reconstructedsingle-particle diffraction pattern can be directly used in common iterative phaseretrieval algorithms to recover the structure of the particle

Dynamics of colloidal crystals studied by pump-probe experiments at FLASH

We present a time-resolved infrared (IR) pump and extreme-ultraviolet (XUV) probe diffraction experiment to investigate ultrafast structural dynamics in colloidal crystals with picosecond resolution. The experiment was performed at the FLASH facility at DESY with a fundamental wavelength of 8 nm. In our experiment, the temporal changes of Bragg peaks were analyzed, and their frequency components were calculated using Fourier analysis. Periodic modulations in the colloidal crystal were localized at a frequency of about 4–5 GHz. Based on the Lamb theory, theoretical calculations of vibrations of the isotropic elastic polystyrene spheres of 400 nm in size reveal a 5.07-GHz eigenfrequency of the ground (breathing) mode

Double Hexagonal Close-Packed Structure Revealed in a Single Colloidal Crystal Grain by Bragg Rod Analysis

A coherent X-ray diffraction study of a single colloidal crystal grain composedof silica spheres is reported. The diffraction data contain Bragg peaks andadditional features in the form of Bragg rods, which are related to the stacking ofthe hexagonally close-packed layers. The profile of the Bragg rod shows distinctintensity modulations which, under the specific experimental conditions usedhere, are directly related to the stacking sequence of the layers. Using a modelfor the scattered intensity along the Bragg rod for an exact stacking sequence ofa finite number of hexagonally close-packed layers, it is found that a doublehexagonal close-packed stacking sequence is present in the colloidal crystalgrain. This analysis method opens up ways to obtain crucial structuralinformation from finite-sized crystalline samples by employing advancedthird-generation X-ray sources

Double hexagonal close-packed structure revealed in a single colloidal crystal grain by Bragg rod analysis

A coherent X-ray diffraction study of a single colloidal crystal grain composed of silica spheres is reported. The diffraction data contain Bragg peaks and additional features in the form of Bragg rods, which are related to the stacking of the hexagonally close-packed layers. The profile of the Bragg rod shows distinct intensity modulations which, under the specific experimental conditions used here, are directly related to the stacking sequence of the layers. Using a model for the scattered intensity along the Bragg rod for an exact stacking sequence of a finite number of hexagonally close-packed layers, it is found that a double hexagonal close-packed stacking sequence is present in the colloidal crystal grain. This analysis method opens up ways to obtain crucial structural information from finite-sized crystalline samples by employing advanced third-generation X-ray sources