X-ray imaging at the nanoscale: holography, tomography and nano-diffraction
Prof. Tim Salditt, Universität Göttingen
X-rays deeply penetrate matter and thus provide information about the functional (interior) architecture of complex samples, from biological tissues and cells to novel composite materials. However, this potential of hard x-rays in view of penetration power, high spatial resolution, quantitative contrast, and compatibility with environmental conditions has to date not been fully developed, mainly due to significant challenges in x-ray optics. With the advent of highly brilliant radiation, coherent focusing, and lens-less diffractive imaging this situation has changed. We show how nano-focused coherent x-ray synchrotron beams can be used for scanning as well as full field x-ray imaging. The central challenge of inverting the coherent diffraction pattern of the recorded hologram is discussed. Examples of biological imaging are presented, ranging from bacterial [1,2] and eukaryotic cells , to nerve tissue, up to the level of organs or small organisms .
In particular, we show how holographic projection images recorded by using the quasi-point source of an x-ray waveguide can be inverted to quantitative two and three dimensional images of biological cells, see Fig.1. The experimental and conceptual aspects of image formation, object reconstruction, contrast transfer function and resolution will be discussed, and illustrated by different examples. In a second step, the medium resolution images can be combined with scanning nano-diffraction yielding high resolution information in real space .
 K. Giewekemeyer,et al., Quantitative biological imaging by ptychographic x-ray diffraction microscopy, PNAS 107 (2), 529 (2010)
 R. N. Wilke, M. Priebe,M. Bartels,K. Giewekemeyer, A. Diaz, P. Karvinen, T. Salditt, Hard X-ray imaging of bacterial cells: nano-diffraction and ptychographic reconstruction, Optics Express, Vol. 20 Issue 17, pp.19232-19254 (2012)
 K. Giewekemeyer, et al. NJP(2010); Giewekemeyer et al, Physical Review (2011).
 C Olendrowitz, M Bartels, M Krenkel, A Beerlink, R Mokso, M Sprung and T Salditt, Phase-contrast x-ray imaging and tomography of the nematode Caenorhabditis elegans, Phys. Med. Biol. 57 (2012) 5309–5323