Abstract
Ptychography is a coherent diffraction imaging (CDI) method for extended objects in which diffraction patterns are acquired sequentially from overlapping coherent illumination spots. The object's complex transmission function can be reconstructed from those diffraction patterns at a spatial resolution limited only by the scattering strength of the object and the detector geometry. Most experiments to date have positioned the illumination spots on the sample using a move-settle-measure sequence in which the move and settle steps can take longer to complete than the measure step. We describe here the use of a continuous "fly-scan" mode for ptychographic data collection in which the sample is moved continuously, so that the experiment resembles one of integrating the diffraction patterns from multiple probe positions. This allows one to use multiple probe mode reconstruction methods to obtain an image of the object and also of the illumination function. We show in simulations, and in x-ray imaging experiments, some of the characteristics of fly-scan ptychography, including a factor of 25 reduction in the data acquisition time. This approach will become increasingly important as brighter x-ray sources are developed, such as diffraction limited storage rings.
Highlights
Ptychography is an imaging method in which a limited-size coherent illumination probe is moved sequentially across an extended object, while the resulting diffraction patterns are collected [1]
While ptychography can be used over a broad spectrum of wavelengths including visible light [2, 10], it has proven to be especially popular in x-ray microscopy
We show here that this is the case, so that ptychography can be implemented in fly-scan mode to dramatically speed up data acquisition while high quality images are obtained by using multiple probe modes in the reconstruction
Summary
Ptychography is an imaging method in which a limited-size coherent illumination probe is moved sequentially across an extended object, while the resulting diffraction patterns are collected [1]. One can mark the increment from one pixel to the by using a timing signal, or use the output of a position feedback system such as a laser interferometer to do position-based scan clocking This approach has long been used in soft x-ray scanning microscopes, and has recently been implemented for hard x-ray scanning fluorescence microscopes as well [27]. An important recent development in ptychography has shown that the redundancy of information provided by overlapping probe positions offers the opportunity to reconstruct multiple modes of the object and/or probe [28] This allows one to use partially coherent illumination, since it can be represented by a small number of self-coherent, but mutually incoherent, optical modes [29, 30]; it allows one to deal with some degree of sample vibration in step-scan ptychography [31]. We show here that this is the case, so that ptychography can be implemented in fly-scan mode to dramatically speed up data acquisition while high quality images are obtained by using multiple probe modes in the reconstruction
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