Using of X-rays demands the high degree of a spatial coherence in order to obtain far-field diffraction patterns with speckle patterns. This property is necessary in order to perform coherent diffraction imaging CDI and ptychographic experiments. Coherent X-ray beams could be produced by modern synchrotron radiation sources, free electron lasers.
In diffraction experiment only intensities of scattered radiation can be recorded. All phase information is lost. The phase problem also can be solved in this case with application of a certain constraints. However with the single exposure diffraction pattern there is a limitation on the size of the investigated sample. It should be less that transverse size of the coherent part of the beam. Also it is also not trivial to make the reconstruction to converge to a stable solution.
The idea of X-ray ptychography is to scan an extended sample trough the beam while adjacent probe spots overlap significantly in the object plane. This produce a redundancy of the diffracted data which could be inverted with ptychographical iterative engine algorithm PIE. Its main advantages are noise tolerance, high speed of convergence and possible high resolution of reconstructed images.
4 Related Topics about PtychographyBragg reflections .. Walter Hoppe .. phase problem .. reciprocal lattice ..