More coherent x-ray lens-less image reconstructions

New paper in Science by Pierre Thibault et al. “High-Resolution Scanning X-ray Diffraction Microscopy” Science 321, 379 (2008).

Authors use an approach identical to ptychography  to demonstrate the power of the technique by reconstructing the Fresnel Zone Plate – similar to work by Rodenburg et al., PRL 98, 034801 (2007).

John Miao and his UCLA group has used lensless imaging to reconstruct image of a single virus:

C. Song et al., “Quantitative Imaging of Single, Unstained Viruses with Coherent X-rays” arXiv:0806.2875.

And Stadler et al. “Hard X Ray Holographic Diffraction Imaging” Phys. Rev. Lett. 100, 245503 (2008) show that the x-ray holographic approach similar to the one previously used by Eisebitt et al., Nature 432, 885 (2004) works in hard-xray regime as should be expected. They cleverly used five carefully positioned nanoparticles as the negative sources of reference beam, and successfully demonstrated that letter “P” can be reconstructed, adding to an impressive alphabet of reconstructed letters and logos. While use of hard x-rays paves the road for imaging of thick speciments, it’s not clear if one could take advantage of the same principle in high-angle diffraction geometry, which is where real action is for hard x-rays.

two PRLs on x-ray phasing

Two new PRLs are dealing with x-ray phasing.

The first paper is de Jonge et al., “Quantitative Phase Imaging with a Scanning Transmission X-Ray Microscope” Phys. Rev. Lett. 100, 163902 (2008). Typically the differential phase contrast measurements become non-trivial for thick specimens, when the adsorption and phase-wrapping effects become significant. This paper resolves this problems when differential phase contrast measurements are done in scanning transmission x-ray microscopy mode (STXM), since the solution is overconstrained, allowing to arrive at unique phase and adsorption values.

The second paper is Johnson et al., “Coherent Diffractive Imaging Using Phase Front Modifications” Phys. Rev. Lett. 100, 155503 (2008).

Since phase is lost during the measurements, it is impossible to simply fourier-transform the coherent x-ray diffraction pattern to obtain a real-space image of an object with nanoscale resolution. There are numerous numerical approaches of phase-retrieval based on oversampling the diffraction pattern. This paper presents an alternative approach of introducing a phase plate, and deconvolving the set of phases resulting from the sample by scanning the phase object around, making the contribution from the phase plate known, and providing information on un-altered phases that would be observed if no phase plate was present. This technique is similar to ptychography, as it provides additional constraints that help arriving at unique solution in a rapidly convergent manner, except it scans the known phase plate, rather than the object being imaged.