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Ptychography (1) Basic Concept

Coherent Diffractive Imaging

[1]
Also known as lensless imaging, is based on the retrieval of a complex sample structure (phase) from a measurement of scattered radiation intensity from a coherently illuminated sample out of the imaging plane.

 [2]
Coherent diffractive imaging (CDI) is an alternative technique that promises, in theory, to allow imaging of specimens at a resolution limited only by the wavelength of the illuminating radiation. CDI replaces the imaging optics and their associated imperfections, with a solution to an inverse problem (phase problem). The inversion step involves determining the complex exit-surface wave function from the recorded intensity, which in the case of diffractive imaging is in the far field.  Reconstruction of the full complex exit wave recovers the amplitude and phase of the specimen transmission function, related to physical properties of the specimen. CDI involves a non-linear inverse problem and the consequent issue of the non-uniqueness of the solution is exacerbated by the deleterious effects of measurement noise. One approach for circumventing these problems has been the introduction of so-called phase diversity in the probing radiation, most commonly by using overlapping probe positions with respect to the sample, and performing multiple measurements
to over-determine the inverse problem

Ptychography 

[1]
A scanning coherent diffractive imaging (CDI) technique.

 [2]
Electron ptychography has the advantage that it can provide information at atomic resolution but this has been demonstrated only relatively recently and requires extremely high experimental stability with respect to both the probe shape and position. The advantage of ptychography is that measurement noise between adjacent probe positions is uncorrelated and, provided that the inverse problem is well posed, results in a reconstruction that is more robust and dose efficient when compared with CDI techniques using a single probe position.
ref:
[1] https://doi.org/10.1364/OE.24.008360
[2] http://dx.doi.org/10.1063/1.4941269
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