篭島 靖

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.

A novel type of zone plate (ZP), termed an inverse-phase composite ZP, is proposed to gain a deeper focus than the standard diffraction-limited depth of focus, with little reduction in spatial resolution. The structure is a combination of an inner ZP functioning as a conventional phase ZP and an outer ZP functioning with third-order diffraction with opposite phase to the inner ZP. Two-dimensional complex amplitude distributions neighboring the focal point were calculated using a wave-optical approach of diffraction integration with a monochromatic plane-wave illumination, where one dimension is the radial direction and the other dimension is the optical-axis direction. The depth of focus and the spatial resolution were examined as the main focusing properties. Two characteristic promising cases regarding the depth of focus were found: a pit-intensity focus with the deepest depth of focus, and a flat-intensity focus with deeper depth of focus than usual ZPs. It was found that twice the depth of focus could be expected with little reduction in the spatial resolution for 10 keV X-ray energy, tantalum zone material, 84 nm minimum fabrication zone width, and zone thickness of 2.645 µm. It was also found that the depth of focus and the spatial resolution were almost unchanged in the photon energy range from 8 to 12 keV. The inverse-phase composite ZP has high potential for use in analysis of practical thick samples in X-ray microbeam applications.