Ptychography

Article summary

Ptychography (/t(a)ɪˈkɒgrəfi/ t(a)i-KO-graf-ee) is a computational microscopy technique that reconstructs the complex-valued image (amplitude and phase) of a specimen from a series of coherent diffraction patterns recorded as a localized probe is scanned with overlap across the sample. It unifies the principles of microscopy and crystallography, combining the real-space imaging of microscopy with the reciprocal-space diffraction analysis of crystallography to produce high-resolution, quantitative images free from lens aberrations. Ptychography has been demonstrated with visible light, X-rays, electrons and extreme-ultraviolet radiation, enabling quantitative phase contrast imaging across nine orders of magnitude in length scales. Its defining characteristic is translational invariance, which means that the interference patterns are generated by one constant function (e.g. a field of illumination or an aperture stop) moving laterally by a known amount with respect to another constant function (the specimen itself or a wave field). The interference patterns occur some distance away from these two components, so that the scattered waves spread out and "fold" ( , "ptychē" is 'fold' ) into one another as shown in the figure. Unlike conventional lens imaging, ptychography is unaffected by lens-induced aberrations or diffraction effects caused by limited numerical aperture.…

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