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Overview

Theo Murphy meeting organised by Professor John Rodenburg FRS, Professor Ian Robinson and Dr Andrew Maiden.

Ptychography is a form of computational imaging that has distinct advantages over conventional microscopic imaging methods. This meeting will bring together researchers from the X-ray community, who have been using ptychography for about 15 years, with more recent adopters of the technique from the visible light, EUV and electron microscopy communities, as well as theoreticians studying novel applications and algorithms relating to the technique.

The schedule of talks and speaker biographies are available below. Speaker abstracts are also available below.

Poster session

There will be a poster session on Monday 23 October. If you would like to apply to present a poster please submit your proposed title, abstract (not more than 200 words and in third person), author list, name of the proposed presenter and authors' institutions to the Scientific Programmes team no later than Friday 29 September. Please include the text ‘Poster abstract submission’ in the email subject line. Please note that places are limited and are selected at the scientific organisers discretion.

Attending this event

This event is intended for researchers in relevant fields, and is a residential meeting taking place at the Randolph Hotel, Beaumont Street, Oxford, OX1 2LN.

  • Free to attend
  • Advance registration essential (please request an invitation)
  • This is an in-person meeting
  • Catering options are available to purchase during registration. Participants are responsible for their own accommodation booking.

To view the programme, please scroll down and select the day on the left-hand side. Click the arrows to view the speakers and talks.

Enquiries: contact the Scientific Programmes team

Organisers

Schedule


Chair

09:00-09:05
Introduction
09:05-09:30
Beyond the limitations of traditional imaging: advancements in nanoscale 3D X-ray imaging with ptychography and sparsity

Abstract

Ptychography, and in particular its extension to 3D, is a powerful technique that allows nanoscale material characterization with quantitative electron density contrast. Extensions of the technique to the spectral or time domain offer unique opportunities to study operando materials and to do quantitative chemical mapping. However, being a scanning technique, extensions to higher dimensions can require prohibitive scanning times. Here Professor Guizar-Sicairos will present results that combine ptychographically acquired projections with tomographic sparsity in order to significantly improve the time or spectral resolution, with application to energy conversion materials.

Speakers

09:30-09:45
Discussion
09:45-10:15
Making every electron count; ptychography at low dose

Speakers

10:15-10:30
Discussion
10:30-11:00
Break
11:00-11:30
Dichroic X-ray ptychography of 3D magnetic textures

Abstract

Three dimensional magnetic systems promise significant opportunities for both fundamental physics, and technological applications, for example providing higher density devices and new functionalities associated with complex topology and greater degrees of freedom. 

One of the main challenges comes with characterising complex three dimensional magnetic systems. Here Dr Donnelly will discuss the advances in X-ray magnetic tomographic imaging making use of dichroic X-ray ptychography. Using hard X-ray magnetic tomography, we have been able to map both the static configuration, and dynamical behaviour, of topological magnetic structures. Understanding these complex configurations is challenging: recent advances in analytical techniques have provided new capabilities to locate and identify 3D magnetic solitons, leading to the first observation of nanoscale magnetic vortex rings. 

While hard X-ray imaging offers high resolution imaging of extended magnetic systems, the weak magnetic dichroism limits the variety of materials that can be imaged. To this end, Dr Donnelly will present recent results of soft X-ray dichroic ptychography where the phase dichroism offers a route to imaging magnetic systems that until now have not been accessible.

These new capabilities for the high spatial resolution imaging of three dimensional magnetic configurations opens the door to the exploration of both fundamental and technologically relevant magnetic systems.

 

Speakers

11:30-11:45
Discussion
11:45-12:15
Bragg ptychography

Abstract

Bragg ptychography is a phase retrieval method combining crystalline sensitivity and the possibility to image extended 3D samples. Recent progresses in Bragg ptychography formalism, namely, the introduction of the Bragg projection operator and the advent of 4th generation synchrotron sources have enabled the use of 3D Bragg ptychography with unprecedented accuracy, sensitivity and spatial resolution. Specifically, the probe retrieval and the beam-position refinement are now possible thanks to the amount of information encoded in the diffraction patterns produced with extremely brilliant source. Together with collaborators from ESRF, MAXIV and Diamond, Dr Chamard's group is now pushing forward the integration of Bragg ptychography at synchrotron beamlines to enable the use of this 3D crystalline microscopy approach to a larger x-ray community. In this talk, Dr Chamard will review the history of Bragg ptychography and highlight the pending questions related to the dissemination of the method.

Speakers

12:15-12:30
Discussion
13:30-14:00
Evaluating the performance of electron ptychography at low dose

Abstract

Many materials of interest for energy storage and energy conversion present two important challenges when attempting to characterise at high resolution using electrons. First, they often contain low atomic-number elements such as lithium and oxygen. Second, they are often susceptible to damage under electron irradiation. Electron ptychography is a very promising technique to overcome both these challenges because it allows detection of the small phase shifts induced on a transmitted electron wave and it can make use of a large fraction of the transmission electrons thereby maximising the information per damage event. Comparisons of ptychographic images from a range of samples with those formed using phase contrast TEM (as is used in cryo-TEM for biological samples) suggests that ptychography is very competitive.

In this talk Professor Nellist will explore some of the important attributes of electron ptychography for comparison with other techniques. The effects of partial spatial and temporal coherence will be discussed. Suitable metrics to allow comparison between different imaging modes will be explored and initial results presented. The discussion will be illustrated with applications of ptychography to battery materials and polymers.

 

Speakers

14:00-14:15
Discussion
14:15-14:45
Provably accurate recovery of compactly supported smooth functions from spectrogram measurements

Abstract

In this talk Professor Iwen will focus on the approximation of smooth functions, up to an unresolvable global phase ambiguity, from a finite set of Short Time Fourier Transform (STFT) magnitude (ie spectrogram) measurements. Algorithms are developed for approximately inverting such measurements, each with theoretical error guarantees establishing their correctness. A detailed numerical study further demonstrates that the algorithms work well in practice and have good numerical convergence behaviour.

This is joint work with Mike Perlmutter (UCLA), Nada Sissouno (TUM), and Aditya Viswanathan (UM-Dearborn).

 

Speakers

14:45-15:00
Discussion
15:00-15:30
Break
15:30-16:00
Framewise network in Ptychographic phase retrieval

Abstract

Most optimization methods in phase retrieval rely on gradients or proximal operators embedding phase less data onto an image space (and an illumination for blind ptychography), however convergence rate of these methods scales poorly with data size. By analysing the relationship network and minimizing the difference between all pairs of overlapping frames, it is possible to identify the slowly evolving principal modes, and solve large scale position drifts, or slow phase variations. Examples applications will be discussed.

Speakers

16:00-16:15
Discussion
16:15-17:00
Poster flash talks

Chair

09:00-09:30
High-resolution, high-throughput coded ptychography for biomedical imaging

Abstract

Ptychography has emerged as a transformative coherent imaging technique for both fundamental and applied sciences. Its applications in optical microscopy, however, often fall short for its relatively low imaging throughput and limited resolution. In this talk, Dr Zheng will discuss a coded ptychography technique that achieves an imaging throughput order of magnitude greater than previous demonstrations. In this platform, we translate the samples across the disorder-engineered surfaces for lensless diffraction data acquisition. The engineered surface can be made by smearing a monolayer of blood on top of the image sensor. The entire system can be built using a modified Blu-ray player, where the 405 nm laser from the optical pickup head can be used as a coherent light source for sample illumination. By tracking the phase wraps of the recovered images, the group reports the direct observation of bacterial growth in a 15-s interval at a 120 mm^2 area, with a phase sensitivity like that obtained from interferometric measurements. They also characterize cell growth via longitudinal dry mass measurement and perform rapid bacterial detection at low concentrations. For drug-screening application, they demonstrate antibiotic susceptibility testing and perform single-cell analysis of antibiotic-induced filamentation. The combination of high phase sensitivity, high spatiotemporal resolution, and ultra-large field of view is unique among existing microscopy techniques. Dr Zheng will also discuss several extensions of the coded ptychography technique, including optofluidic ptychography, synthetic aperture ptychography, and depth-multiplexed on-chip imaging, thereby expanding its applicability in different fields.

Speakers

09:30-09:45
Discussion
09:45-10:15
Ptychography based super-resolution X-ray fluorescence microscopy via deep residual networks

Abstract

Ptychography is a computational method of microscopic imaging that can generate high spatial resolution complex phase information of an object by processing coherent diffraction patterns scattered from the object. With the development of Ptychography, it has been extensively used to study materials in combination with other imaging techniques, which can give multiple contrast mechanisms of the measured sample – for example, in combination with X-ray fluorescence (XRF) microscopy. While Ptychography can achieve diffraction-limited spatial resolution, the used X-ray probe profile information usually limits the resolution of XRF images. In this talk, Dr Wu will present a machine learning based approach utilizing multimodal measurement (ie the combination of Ptychography and XRF microscopy) to enhance the resolution of the corresponding XRF microscopy by deconvolving the X-ray probe from the XRF signal. The enhanced spatial resolution was observed for both simulated and experimental XRF data, showing superior performance over the state-of-the-art scanning XRF method with different nano-sized X-ray probes. Enhanced spatial resolutions were also observed for the accompanying 3D XRF tomography reconstructions.

Speakers

10:15-10:30
Discussion
10:30-11:00
Break
11:00-11:30
Fourier ptychography and its extensions into 3D polarimetry

Abstract

Due to the optically transparent nature of many biological specimens, high-resolution microscopic bio-imaging often requires the use of dyes or fluorescent labels to produce sufficient contrast that are not ideal for many in vivo experiments. By measuring the optical phase delay introduced by semi-transparent tissue, quantitative phase imaging methods like ptychography offer an effective label-free imaging platform. Many transparent specimens also exhibit alternative endogenous optical contrast mechanisms, including anisotropic properties such as material birefringence and orientation. Here, Dr Horstmeyer describes several relatively straightforward extensions of ptychography that allow us to measure this phase-sensitive anisotropic information in 3D. The only hardware modifications required to a standard microscope include two polarization-sensitive optical elements and an LED array for specimen illumination. Dr Horstmeyer then extends the standard Fourier ptychography model and inverse solver to account for the vectorial nature of light, the sample, and the microscope itself, which allows us to computationally remove polarization-dependent imaging system aberrations. He demonstrates and validate large-area, high-resolution volumetric reconstructions of specimen refractive index, birefringence, and orientation for muscle fibre sections and diseased heart tissue, the latter of which carries important information for detecting cardiac amyloidosis.

Speakers

11:30-11:45
Discussion
11:45-12:15
Experiments in near-field ptychography

Abstract

Regardless of wavelength, ptychography is conventionally configured as a far-field method, where dark-field signal is processed to realise super-resolution beyond the aperture of the probe-forming optics. Operating in this high-resolution, lens-free imaging mode, it has proven more-or-less unbeatable. However, ptychography has advantages beyond resolution gains, particularly as a high-accuracy, large field-of-view and experimentally undemanding form of quantitative phase imaging (QPI). Applications here range from unstained imaging of live cells at optical wavelengths to imaging electric and magnetic fields in the electron microscope. For these applications, ptychography in a near-field configuration is appealing because the data requirements are radically reduced: the experiment is easier and quicker, and the reconstruction process quicker and less memory-intensive than far-field ptychography. In this talk Dr Maiden will present his group's work on this near-field form of ptychography and multi-slice ptychography, spanning a huge range of wavelengths from the optical, through X-ray to the electron regimes.

Speakers

12:15-12:30
Discussion

Chair

13:30-14:00
Multi-wavelength ptychography with high-harmonic generation sources

Abstract

High-harmonic generation (HHG) driven by ultrafast lasers is an effective way to produce broadband coherent extreme ultraviolet (EUV) radiation with a table-top setup. Such sources open up the prospect of spectroscopic nanoscale imaging of integrated circuits and biological structures. Given the limitations of high-resolution optical components for EUV radiation, lensless imaging concepts such as ptychography are essential for efficient HHG-based imaging. 

To use the full bandwidth of HHG sources effectively, ptychography is ideally performed with multiple wavelengths in parallel. As perhaps the main requirement for robust image reconstruction is diversity, an important question is how to control the HHG source properties to optimize diversity, among scan positions as well as between wavelengths. A unique property of ptychography is its ability to retrieve the probe field and object response separately, making ptychography a powerful wavefront sensing technique. This feature enables a detailed investigation of the properties of HHG beams, which can be used to study the physics of HHG. 

Dr Witte will present the group's recent work on multi-wavelength HHG-based ptychography, and its applications in EUV imaging and wavefront sensing. Specifically, he will discuss strategies towards efficient spectroscopic imaging, and how the group used ptychographic wavefront sensing to characterize complex HHG beams, and study how properties such as wavefronts and orbital angular momentum transfer from the fundamental beam to the harmonics. 

Speakers

14:00-14:15
Discussion
14:15-14:45
Talk title tbc

Speakers

14:45-15:00
Discussion
15:00-15:30
Break
15:30-16:00
What are the ultimate resolution limits for ptychography?

Abstract

Electron microscopes use electrons with wavelengths of a few picometers, and are potentially capable of imaging individual atoms in solids at a resolution ultimately set by the intrinsic size of an atom. Even with the rapid advances in aberration-corrector technology, both residual aberrations in the electron lenses and multiple scattering of the incident beam inside the sample, the best resolution possible was an order of magnitude worse than this limit. However, with recent advances in detector technology and ptychographic algorithms to unscramble multiple scattering, the resolution of the electron microscope is now limited only by the dose to the sample, and thermal vibrations of the atoms themselves. At high doses, these approaches have allowed us to image the detailed vibrational envelopes of individual atom columns as well as locating interstitial dopant atoms that would be hidden by channelling of the probe with conventional imaging modes. Even the location of all atoms in thin amorphous films now seems within reach. However, as the dose is reduced, so is our ability to robustly reconstruct the object. Challenges in characterizing and predicting performance will be discussed.

Speakers

16:00-16:15
Discussion
16:15-17:00
Panel discussion