page_title: Ptychography
section_title: Bragg ptychography or reflection ptychography
hierarchical_section_title: Ptychography / Optical configurations / Bragg ptychography or reflection ptychography
caption_attribution_description: Diagram showing the setup for reflection or Bragg ptychography.
context_page_description: Ptychography is a computational method of microscopic imaging. It generates images by processing many coherent interference patterns that have been scattered from an object of interest. Its defining characteristic is translational invariance, which means the interference patterns are generated by one constant function moving laterally by a known amount with respect to another constant function. The interference patterns occur some distance away from these two components, so that the scattered waves spread out and ‘fold’ into one another as shown in the figure.
  Ptychography can be used with visible-light, X-rays, extreme ultraviolet or electrons. Unlike conventional lens imaging, ptychography is unaffected by lens-induced aberrations or diffraction effects caused by limited numerical aperture. This is particularly important for atomic-scale wavelength imaging, where it is difficult and expensive to make good quality lenses with high numerical aperture. Another important advantage of the technique is that it allows transparent objects to be seen very clearly.
context_section_description: This geometry can be used either to map surface features or to measure strain in crystalline specimens. Shifts in the specimen surface, or the atomic Bragg planes perpendicular to the surface, appear in the phase of the ptychographic image.
caption: Optical configuration for reflection or Bragg ptychography.
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