May 2015 Archives

Coherent X-ray diffraction imaging is one of a number of recently developed lens-less microscopic techniques giving 2D real space structure when combined with phase retrieval data processing. A team in Shandong University in China has recently published an interesting observation of intact unstained magnetotactic bacteria. It was confirmed that the reconstructed images give some intercellular structures, such as nucleoid, polyβ-hydroxybutyrate granules, and magnetosomes, which have been identified by electron microscopy. The team was also successful in quantification of the density, i.e., it was found that the average density of magnetotactic bacteria is 1.19 g/cm³ from their data. The experiment was done with 5 keV X-ray photons at BL29XU, SPring-8, Japan. For more information, see the paper, "Quantitative Imaging of Single Unstained Magnetotactic Bacteria by Coherent X.ray Diffraction Microscopy", Jiadong Fan et al., Anal. Chem. 87, 5849 (2015).

A research group led by Professor Jorg Evers (Max Planck Institute for Nuclear Physics, Heidelberg, Germany) has recently reported a method for narrowing the spectral width of X-ray pulses by the use of subluminal light propagation. So far, in visible light, slow group velocity such as 17 m/sec has been observed in low temperature sodium gas at 435 nK (see, L. V. Hau et al., Nature, 397, 594 (1999)). The authors intend a similar effect in X-ray wavelength photons by manipulating the optical response of the 14.4 keV Mössbauer resonance of ⁵⁷Fe nuclei. The method combines coherent control, as well as cooperative and cavity enhancements of light-matter interaction in a single setup. It was found that the reduced group velocity of the obtained X-ray pulses is lower than 10^-4 of the speed of the light. For more information, see the paper, "Tunable Subluminal Propagation of Narrow-band X-Ray Pulses", K. P. Heeg et al., Phys. Rev. Lett. 114, 203601 (2015).

Professors D. A. Keen (Rutherford Appleton Laboratory) and A. L. Goodwin (University of Oxford) have recently published an interesting review paper on disordered structures. For many years, crystallographers have determined the structures of many complicated crystals with atomic or even sub-atomic resolution. On the other hand, the structures of disordered systems, which lack the crystalline periodic order, are still not well understood because of the limits of the analytical technique. Correlated disorder is a disorder, but maintains crystallographic signatures, which can be used for classifying the type of disorder. For more information, see the paper, "The crystallography of correlated disorder", D. A. Keen and A. L. Goodwin, Nature, 521, 303 (2015).