Ptychographic Reconstructions Research Articles

Multi-Modal Ptychography: Recent Developments and Applications

Utilisation of partially coherent X-rays in Coherent X-ray Diffraction Imaging (CDI) and X-ray ptychography have brought intense research and developments for the past few years. Generally, data reconstructions convergence can be achieved by considering to incorporate partially coherent X-rays in ptychographic iterative reconstructions algorithms. Recently, exploration of both X-ray probe and sample modes have been studied and it was suggested that sufficient constraints are required to achieve accurate data reconstructions due to the mathematical inseparability of multiple sample modes that are superimposed into a single set of ptychographic intensity patterns. Here we review the multi-modal ptychography that can be used as a new emerging technique to investigate dynamical sample systems with partially coherent X-rays by recent experimental and simulated demonstrations.

Ptychographic imaging with partially coherent plasma EUV sources

Abstract We report on high-resolution lens-less imaging experiments based on ptychographic scanning coherent diffractive imaging (CDI) method employing compact plasma sources developed for extreme ultraviolet (EUV) lithography applications. Two kinds of discharge sources were used in our experiments: a hollow-cathode-triggered pinch plasma source operated with oxygen and for the first time a laser-assisted discharge EUV source with a liquid tin target. Ptychographic reconstructions of different samples were achieved by applying constraint relaxation to the algorithm. Our ptychography algorithms can handle low spatial coherence and broadband illumination as well as compensate for the residual background due to plasma radiation in the visible spectral range. Image resolution down to 100 nm is demonstrated even for sparse objects, and it is limited presently by the sample structure contrast and the available coherent photon flux. We could extract material properties by the reconstruction of the complex exit-wave field, gaining additional information compared to electron microscopy or CDI with longer-wavelength high harmonic laser sources. Our results show that compact plasma-based EUV light sources of only partial spatial and temporal coherence can be effectively used for lens-less imaging applications. The reported methods may be applied in combination with reflectometry and scatterometry for high-resolution EUV metrology.

Ptychographic Imaging of Nano-Materials at the Advanced Light Source with the Nanosurveyor Instrument

We present a new ptychographic x-ray microscope dedicated to soft x-ray tomography and spectromicroscopy of nano-materials at the Advanced Light Source. The microscope utilizes an ultra-stable, high performance scanning mechanism with laser interferometer feedback for sample positioning and a fast frame rate charge-coupled device detector for soft x-ray diffraction measurements. The microscope can achieve point scan rates of 120 Hz with 1 nm RMS positioning accuracy. A high performance data pipeline has been developed which enables real time ptychographic reconstructions and user-friendly operation. This instrument, called The Nanosurveyor, can achieve a spatial resolution at least 10 times finer than the x-ray spot size in both two and three dimensions with sensitivity to electronicand magnetic states of nano-materials. In this paper we demonstrate the tomographic and spectromicroscopic capability of the Nanosurveyor instrument. At high brightness x-ray sources this instrument will enable spectromicroscopy and tomography of materials with diffraction limited spatial resolution.

Procedures for cryogenic X-ray ptychographic imaging of biological samples.

Biological sample-preparation procedures have been developed for imaging human chromosomes under cryogenic conditions. A new experimental setup, developed for imaging frozen samples using beamline I13 at Diamond Light Source, is described. This manuscript describes the equipment and experimental procedures as well as the authors' first ptychographic reconstructions using X-rays.

A computational framework for ptychographic reconstructions.

Ptychography is now a well-established X-ray microscopy tool for synchrotron end-stations equipped with a scanning stage and a pixelated detector. Ptychographic phasing algorithms use information from coherent diffraction to deliver quantitative images of the specimen at a resolution higher than the scanning resolution. These algorithms have traditionally been implemented in software on a per-instrument basis in various degrees of user-friendliness and sophistication. Here, we present Ptypy, a ptychography software written with the intention to serve as a framework across the diverse sets of available instruments and usage cases. A distinctive feature of the software is its formalism, which provides a convenient abstraction of the physical model, thus allowing for concise algorithmic implementations and portability across set-up geometries. We give an overview of the supported usage cases, explain the abstraction layer and design principles, and provide a step-by-step guide describing how an algorithm may be realized in a concise and readable manner. The software capabilities are illustrated with reconstructions from visible light and X-ray data.

Holography-guided ptychography with soft X-rays.

Ptychography is a lensless imaging technique that aims to reconstruct an object from a set of coherent diffraction patterns originating from different and partially overlapping sample illumination areas. For a successful convergence of the iterative algorithms used, the sample scan positions have to be known with very high accuracy. Here, we present a method that allows to directly encode this information in the diffraction patterns without the need of accurate position encoders. Our approach relies on combining ptychography with another coherent imaging method, namely Fourier-transform holography. We have imaged two different objects using coherent soft-X-ray illumination and investigate the influence of experimental and numerical position refinement on the reconstruction result. We demonstrate that holographically encoded positions significantly reduce the experimental and numerical requirements. Our ptychographic reconstructions cover a large field of view with diffraction-limited resolution and high sensitivity in the reconstructed phase shift and absorption of the objects.

Advances and challenges in cryo ptychography at the Advanced Photon Source.

Ptychography has emerged as a nondestructive tool to quantitatively study extended samples at a high spatial resolution. In this manuscript, we report on recent developments from our team. We have combined cryo ptychography and fluorescence microscopy to provide simultaneous views of ultrastructure and elemental composition, we have developed multi-GPU parallel computation to speed up ptychographic reconstructions, and we have implemented fly-scan ptychography to allow for faster data acquisition. We conclude with a discussion of future challenges in high-resolution 3D ptychography.

Ptychographic x-ray imaging of surfaces on crystal truncation rod

Ptychography is a high-resolution imaging technique, which does not require lenses for image magnification and which provides phase contrast with high sensitivity. Here, we propose to use x-ray ptychography for the imaging of surface structure in crystalline samples. We show that ptychography can be used to image atomic step structures using coherent diffraction patterns recorded along the crystal truncation rod of a crystal surface. In a proof-of-concept experiment on a Pt (111) sample, we present ptychographic reconstructions showing features consistent with surface steps. Due to the penetration power of x-rays, this method could find interesting applications for the study of surface structures under buried interfaces or in harsh environments.

Soft X-ray spectromicroscopy using ptychography with randomly phased illumination

Ptychography is a form of scanning diffractive imaging that can successfully retrieve the modulus and phase of both the sample transmission function and the illuminating probe. An experimental difficulty commonly encountered in diffractive imaging is the large dynamic range of the diffraction data. Here we report a novel ptychographic experiment using a randomly phased X-ray probe to considerably reduce the dynamic range of the recorded diffraction patterns. Images can be reconstructed reliably and robustly from this setup, even when scatter from the specimen is weak. A series of ptychographic reconstructions at X-ray energies around the L absorption edge of iron demonstrates the advantages of this method for soft X-ray spectromicroscopy, which can readily provide chemical sensitivity without the need for optical refocusing. In particular, the phase signal is in perfect registration with the modulus signal and provides complementary information that can be more sensitive to changes in the local chemical environment.

Quantitative phase contrast optimised cancerous cell differentiation via ptychography

This paper shows that visible-light ptychography can be used to distinguish quantitatively between healthy and tumorous unstained cells. Advantages of ptychography in comparison to conventional phase-sensitive imaging techniques are highlighted. A novel procedure to automatically refocus ptychographic reconstructions is also presented, which improves quantitative analysis.