SHARP: a distributed GPU-based ptychographic solver

Abstract

Ever brighter light sources, fast parallel detectors and advances in phase retrieval methods have made ptychography a practical and popular imaging technique. Compared to previous techniques, ptychography provides superior robustness and resolution at the expense of more advanced and time-consuming data analysis. By taking advantage of massively parallel architectures, highthroughput processing can expedite this analysis and provide microscopists with immediate feedback. These advances allow real-time imaging at wavelengthlimited resolution, coupled with a large field of view. This article describes a set of algorithmic and computational methodologies used at the Advanced Light Source and US Department of Energy light sources. These are packaged as a CUDA-based software environment named SHARP (http://camera.lbl.gov/ sharp), aimed at providing state-of-the-art high-throughput ptychography reconstructions for the coming era of diffraction-limited light sources.

Model-independent noise-robust extension of ptychography

“…Previous proposals for noise robust ptychographic algorithms mainly revolved around assuming a known noise model, and using a maximum-likelihood optimization scheme [10,11] or a variance-stabilizing scheme [12][13][14] to construct a cost function which, when minimized, yields a superior reconstruction, because prior knowledge of the noise model has been incorporated. In this section, we discuss the methods in more detail to see where there is room for improvement in these reconstruction schemes, which is what motivated the development of the algorithm that is proposed in this article.…”

“…An alternative method uses variance stabilizing transforms [12][13][14]. Also in this scheme a noise model needs to be assumed.…”

“…We propose an extension to the ptychographic algorithm that can be applied to any of the aforementioned algorithms [10][11][12][13][14], does not require an assumed noise model, and works by adapting the intensity constraints. We test the algorithm with a proof-of-principle experiment in the visible light regime where we use a phase-only Spatial Light Modulator (SLM) to create and shift the object.…”

Measuring spectroscopy and magnetism of extracted and intracellular magnetosomes using soft X-ray ptychography

“…The measured ptychography images were reconstructed using 200 iterations of the relaxed averaged alternating reflection (RAAR) algorithm implemented in the SHARP Center for Applied Mathematics for Energy Research Applications ptychography code (62,63). Illumination and incoherent background refinements were used in every other iteration.…”

X-Ray Near-Field Holography: Beyond Idealized Assumptions of the Probe

“…Aiming at more appropriate schemes to treat the data, recent work has introduced the concept of simultaneous reconstruction of probe and object to near-field (propagation) imaging [13,14]. This was achieved by a suitable generalization and extension of the ptychographic algorithms initially developed for confined beams (typical for far-field diffractive imaging) [59][60][61][62][63][64]. In [13,65], the object was scanned transversally in the extended wave field behind a wavefront diffuser, in order to increase the diversity of the probe.…”