Multi-slice ptychographic tomography

Peng Li,Andrew Maiden

doi:10.1038/s41598-018-20530-x

Abstract

Ptychography is a form of Coherent Diffractive Imaging, where diffraction patterns are processed by iterative algorithms to recover an image of a specimen. Although mostly applied in two dimensions, ptychography can be extended to produce three dimensional images in two ways: via multi-slice ptychography or ptychographic tomography. Ptychographic tomography relies on 2D ptychography to supply projections to conventional tomographic algorithms, whilst multi-slice ptychography uses the redundancy in ptychographic data to split the reconstruction into a series of axial slices. Whilst multi-slice ptychography can handle multiple-scattering thick specimens and has a much smaller data requirement than ptychographic tomography, its depth resolution is relatively poor. Here we propose an imaging modality that combines the benefits of the two approaches, enabling isotropic 3D resolution imaging of thick specimens with a small number of angular measurements. Optical experiments validate our proposed method.

Highlights

Ptychography is most often implemented as a two-dimensional technique, producing phase images that represent a projection of the optical path length through a sample[1,2]
We propose using the limited 3D information from multi-slice ptychography to reduce the number of angular measurements needed for ptychographic tomography, whilst increasing the sample thickness that tomography can accommodate and retaining its high isotropic 3D resolution
We have demonstrated experimentally that the combination of multi-slice ptychography and tomography (MSPT) is able to extend the depth of field and image a 3D sample that is beyond the ability of single-slice ptychographic tomography (SSPT), where single-slice ptychography is used to reconstruct the projections needed for the tomographic reconstruction

Summary

Introduction

Ptychography is most often implemented as a two-dimensional technique, producing phase images that represent a projection of the optical path length through a sample[1,2]. This requires that the sample is optically thin, such that it falls within the multiplicative approximation where the wavefront that passes through a sample can be accurately modelled as the multiplication of the incident illumination function and a sample transmission function[3,4,5]. Ptychography needs dense translational scans because of the overlap constraint[15] and tomography needs dense angular scans because of the Crowther Limit[16] Together these factors result in experiments of many hours[8,10]. This model computationally sections the thick sample into a set of thin slices, each of which falls within the multiplicative www.nature.com/scientificreports/

Methods

Results

Conclusion