Mmmm… PIE!

The title should be pronounced using your best Homer Simpson voice.

PIE stands for “Ptychographical Iterative Engine”, and it’s the most interesting development in lens-less imaging this year. The idea is to use diffraction patterns from overlapping regions (which look like a Venn diagram, or olympic logo) by moving an aperture by a known amount, and use this knowledge to speed up real-space reconstruction process.

The most recent PRL paper is by John Roderburg, and was listed in my GoogleNews feed soon after it came out in January of this year. This most recent work is an experimental extension of simulations done previously by Faulkner and Rodenburg.

There is obviously a great deal of other work done in this area previously by a number of groups, and sooner or later they will be described here. But during this week’s annual Advanced Photon Source Users Meeting I enjoyed a talk on ptychography by Franz Pfeiffer of PSI. There were a lot of other excellent talks on phase retrieval methods/lens-less imaging.

A major struggle with phase retrieval methods is making sure that the convergence is reached quickly and inambiguously – that is, independently from initial phase assumptions. Ptychography reduces number of iterations from many thousands to about a hundred, and can be applied to extended objects. Previous experimental work primarily dealt with nanosized objects – for example nanoparticles, and coherent x-ray beams larger than the imaged object.

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