Yasushi Kagoshima

Abstract In coherent X-ray diffraction imaging, speckles on a coherent diffraction pattern must be sampled at intervals sufficiently finer than the Nyquist interval, which imposes an upper limit on the sample size. To overcome the size limitation, a sub-pixel shift method for upsampling coherent diffraction patterns was proposed. This paper reports on the evaluation of the noise tolerance of the upsampling algorithm by a simulation. The quality of the images reconstructed from the upsampled diffraction pattern and pattern recorded by a detector with an equivalent pixel size was comparable when the optimum number of upsampling iterations is adopted.

<title>Abstract</title>The quest for understanding the structural mechanisms of material properties and biological cell functions has led to the active development of coherent diffraction imaging (CDI) and its variants in the hard X-ray regime. Herein, we propose multiple-shot CDI, a full-field CDI technique dedicated to the visualisation of local nanostructural dynamics in extended objects at a spatio-temporal resolution beyond that of current instrumentation limitations. Multiple-shot CDI reconstructs a “movie” of local dynamics from time-evolving diffraction patterns, which is compatible with a robust scanning variant, ptychography. We developed projection illumination optics to produce a probe with a well-defined illumination area and a phase retrieval algorithm, establishing a spatio-temporal smoothness constraint for the reliable reconstruction of dynamic images. The numerical simulations and proof-of-concept experiment using synchrotron hard X-rays demonstrated the capability of visualising a dynamic nanostructured object at a frame rate of 10 Hz or higher.

Abstract The optical transfer function (OTF) of an inverse-phase composite zone plate under incoherent illumination was numerically evaluated by convoluting the point spread function (PSF) and transmission distribution of a model sample with gradually changing spatial frequency. The PSF used in the simulation was obtained from our previous study on deep-focusing X-ray microscopes. As expected, the contrast in the sample image was lesser than that produced by a conventional zone plate. Phase-reversed contrast—spurious resolution—appeared at a high spatial frequency. Although the calculated OTF is slightly aberrated, its deep-focusing capability is advantageous for X-ray microimaging of thick samples.