An autofocusing algorithm for ptychography is proposed. The method optimizes a sharpness metric that would be observed in a differential interference microscope and is valid for both amplitude and phase modulating specimens. We experimentally demonstrate that the algorithm, based on the extended ptychographic iterative engine (ePIE), calibrates the sample–detector distance with an accuracy within the depth of field of the ptychographic microscope. We show that the method can be used to determine slice separation in multislice ptychography, provided there are isolated regions on each slice of the specimen that do not axially overlap.

Atomic and Molecular Physics, and Optics
OSA Publishing
NWO , ERC
dx.doi.org/10.1364/ol.389492
Opt. Lett.
EUV Generation & Imaging

Loetgering, L, Du, M, Eikema, K.S.E, & Witte, S. (2020). zPIE: an autofocusing algorithm for ptychography. Opt. Lett., 45(7), 2030–2033. doi:10.1364/ol.389492