Real and reciprocal space X-ray imaging

• Professor Ian Robinson, University College London, UK

Biography

Professor Robinson’s research interest is X-ray diffraction using synchrotron radiation (SR). During the Bell Labs years, he developed the methods for studying surface structure using X-ray diffraction. These methods, based on crystal truncation rods, have become the definitive technique for the determination of the atomic positions at surfaces and interfaces. These surface methods are still used today at the major SR facilities, NSLS (Brookhaven), ESRF (Grenoble), APS(Chicago) and SLS (Villigen). He was awarded two prizes for the surface structure work, the Warren Prize in 2000 and the Surface Structure Prize in 2011. To develop the methodology of X-ray diffraction with SR, he built two beamlines. The first was a dedicated surfaces and interface structure beamline X16A at the National Synchrotron Light Source (Brookhaven). The second was 34-ID for coherent diffraction at the Advanced Phoyon Source(Chicago). More recently he has been developing methods of using the very high coherence of the latest SR sources to enable direct 3D imaging of structure. This is potentially useful for examining strain distributions inside complex materials on the nanometre length scale.The coherent X-ray diffraction methods will develop and expand further at the Diamond Light Source (DLS) located at Rutherford Appleton Lab (RAL) near Oxford. He is a founding "Diamond Fellow" of the Research Complex at Harwell (RCaH), also located at RAL. This is a meeting place of physical and live scientists interested in the transfer of methodologies from the physical to the life sciences. Materials and biological imaging are the main directions under development there. Three major grants are supporting the work of his group, which is now divided between the UCL and RCaH centres. The first, entitled "nanosculpture", looks at strains induced in nanometre-sized crystals either synthesised from atoms in a 'bottom up' procedure, or else carved by lithography from bulk materials in a 'top down' approach. The second is to study the structure of the human chromosome by X-ray imaging methods. The third is to develop new X-ray imaging methods based on deliberate modulation of the phase by suitably developed X-ray optics.

• Dr Alessandro Olivo, University College London, UK

Biography

Dr Olivo obtained his undergrad (1995) & postgrad (1999) degrees from the University of Trieste in Italy, starting his PhD after a short stint as a hospital physicist. After the PhD he was employed for 5 years by the same university to develop and support the imaging beamline at the local synchrotron. After participating in the design of the station for in vivo synchrotron mammography, he applied for a Marie Curie Fellowship, on the basis of which he moved to UCL where he started working on the translation of synchrotron techniques into laboratory environments. Soon afterwards, he was awarded an EPSRC Career Acceleration Fellowship and then a Challenging Engineering grant, which led to his current Senior Lectureship. On the basis of these and other grants, he has set up an x-ray phase contrast lab and currently lead an 8-strong group to develop and apply the technique in a variety of fields including radiology, biology, material science and security.

• Dr Janos Kirz, Advanced Light Source, USA

Biography

Janos Kirz is Distinguished Professor Emeritus at Stony Brook University, where he led a group in the development of X-ray microscopy, and served as Chair of the Department of Physics and Astronomy between 1998 and 2001. He is also Scientific Advisor at the Advanced Light Source in Berkeley, where he was Acting Director of the facility between 2004 and 2006. He chairs the Scientific Council for the DESY laboratory in Hamburg, the Proposal Review Panel for the free electron laser FERMI in Trieste and the Policy and Advisory Board for CHESS at Cornell University. During fall 2011 he was Visiting Professor of the Academia Sinica at the University of Science and Technology of China in Hefei.

Selected recent publications:

An assessment of the resolution limitation due to radiation-damage in x-ray diffraction microscopy,  M R Howells et al. J Electron Spect Rel Phenomena  170, 4-12 (2009)

Soft X-ray Diffraction Microscopy of a Frozen Hydrated Yeast Cell,  X Huang et al, Phys Rev Lett 103, 198101 (2009)

High resolution x-ray diffraction microscopy of specifically labeled yeast cells, J Nelson et al, PNAS 107, 7235-7239 (2010)

New Directions in X-ray Microscopy, R Falcone et al, Contemporary Physics 52, 293-317 (2011)

• Dr Gerd Schneider, Helmholtz-Zentrum Berlin, Germany
• Audio recording (mp3)

Biography

Priv Doz Dr Gerd Schneider received his PhD in physics from the University of Göttingen in 1992. After his habilitation in 2009 he joined Berkeley Lab. Since 2003 he is head of the X-ray microscopy team at the Helmholtz Zentrum Berlin.  His main working area is in the field of x-ray imaging, x-ray optics and synchrotron radiation.  He has also extensive experience in x-ray microscopy applications in life and materials sciences. Gerd developed together with his team the new full-field cryo-tomography x-ray microscope at HZB which is unique in terms of spectral resolution of E/DE=10.000 and spatial resolution of 10 nm.  Its application fields range from NEXAFS spectromicroscopy and nanoscale tomography of cryogenic cells up to dynamic studies of failure mechanism in microprocessors.  

Selected publications:

Ultrahigh-Resolution Soft-X-Ray Microscopy with Zone Plates in High Orders of Diffraction, S Rehbein et al, Phys Rev Lett 103, 110801 (2009)
Three-Dimensional Cellular Ultrastructure Resolved by X-Ray Microscopy, G. Schneider et al, Nature Methods 7 (2010), 985-987
Nanoscale spectroscopy with polarized X-rays by NEXAFS-TXM, P. Guttmann et al., Nature Photonics 6 (2012), 25-29
Cryo X-ray microscope with flat sample geometry for correlative fluorescence and nanoscale tomographic imaging, G Schneider et al, J Struct Biol 177 (2012), 212-223
Oriented nucleation of hemozoin at the digestive vacuole membrane in Plasmodium falciparum, S Kapishnikov et al, PNAS 109, no.28 (2012), 11188-11193

Abstract

X-ray imaging offers a new 3-D view into cells. With its ability to penetrate whole hydrated cells it is ideally suited for pairing fluorescence light microscopy and nanoscale X-ray tomography. In the talk, we describe the X-ray optical set-up and the design of the cryo full-field transmission X-ray microscope (TXM) at the electron storage ring BESSY II. Compared to previous TXM set-ups with zone plate condenser monochromator, the new X-ray optical layout employs an undulator source, a spherical grating monochromator and an elliptically shaped glass capillary mirror as condenser. This set-up improves the spectral resolution by an order of magnitude. Furthermore, the partially coherent object illumination improves the contrast transfer of the microscope compared to incoherent conditions.

With the TXM, cells grown on flat support grids can be tilted perpendicular to the optical axis without any geometrical restrictions by the previously required pinhole for the zone plate monochromator close to the sample plane. We also developed an incorporated fluorescence light microscope which permits to record fluorescence, bright field and DIC images of cryogenic cells inside the TXM. Scientific results in the application fields of life and material sciences will be presented.

• Dr Wataru Yashiro, Tohoku University, Japan
• Audio recording (mp3)

Biography

Dr Wataru Yashiro is an associate professor of Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University. He received phD degree in 2000 from the University of Tokyo, Japan. He was a research associate of Japan Society for the Promotion of Science (JSPS) from 2000 to 2001, National Institute of Advanced Industrial Science and Technology (AIST), Japan, from 2001 to 2004, National Institute of Materials Science (NIMS), Japan, in 2004, and Graduate School of Frontier Sciences (GSFS), the University of Tokyo, Japan, from 2004 to 2005. In 2005, he became an assistant professor of GSFS, the University of Tokyo. In July 2012, he moved from to Tohoku University, and is now an associate professor of IMRAM.

He is a specialist of X-ray optics (X-ray surface crystallography, X-ray imaging, and dynamical X-ray diffraction). He also has research experiences in the fields of crystal growth and micro-nano fabrication.

AWARD: Award for Yong Scientist of the Japanese Society for Synchrotron Radiation Research (2005); Denver X-ray Conference, XRD Award (2005); Award for Encouragement of Research in Materials Science; the Materials Research Society of Japan (2006); Image Science Encouraging Award, Konica Minolta Science and Technology Foundation (2011).

Abstract

Non-destructive and quantitative nanometer-scale imaging of internal structures of materials consisting of light elements will bring dramatic progress in life and material sciences. For a microscopic imaging technique, not only its spatial resolution but also its sensitivity is a key factor that determines its performance. Use of phase shift of X-rays provides a solution to drastically improve the sensitivity. In this presentation I will talk about phase-sensitive X-ray imaging microscopes we have recently proposed [1-3], which are based on a self-imaging phenomenon (called ‘Talbot effect’) of a transmission grating. I will also show preliminary experimental results of an X-ray projection microscope using a transmission grating for higher sensitivity and spatial resolution.

[1] W Yashiro et al, Phys Rev Lett 103 (2009) 180801.
[2] W Yashiro et al, Phys Rev A 82 (2010) 043822.
[3] H Kuwabara, et al, Appl Phys Exp 4 (2011) 062502.

• Professor Chris Jacobsen, Argonne Lab/Northwestern University, USA
• Audio recording (mp3)

Biography

Chris Jacobsen is an Associate Division Director at the Advanced Photon Source (APS) at Argonne, and a Professor of Physics at Northwestern University (where he's also in the Chemistry of Life Processes Institute).  His interests are in x-ray optics and microscopy, both in method and instrumentation development and in biological and environmental science applications.  He is a fellow of the American Association for the Advancement of Science, the American Physical Society, and the Optical Society of America, and he has received awards including a Presidential Faculty Fellowship (White House/National Science Foundation), the Denis Gabor Award (Hungary), and the Kurt Heinrich Award (Microbeam Analysis Society).

Abstract

Ptychography provides an approach for coherent diffraction imaging of extended specimens as well as recovery of the phase response, which is the dominant contrast mechanism for hard x-ray imaging of light materials.  We describe efforts towards combining these capabilities of ptychography with x-ray fluorescence microprobe analysis of trace elements in biological specimens.  Ptychography should allow us to see the fine structure in cells and thus place metals and other trace elements in their correct biological context, and use of a cryogenic microscope will allow us to do this on samples with excellent preparation fidelity.  Progress on room temperature ptychography, on fast scanning methods, and on measurements of scanning position distortions in the cryogenic microscope will be described, with a perspective to ongoing experiments.

• Professor John Spence, Arizona State University and Lawrence Berkeley Laboratory, USA
• Audio recording (mp3)

Biography

John Spence is Regent's Professor of Physics at Arizona State University (where he teaches condensed matter physics) with a joint appointment at Lawrence Berkeley Laboratory. He completed his PhD at Melbourne University in Physics in 1973 and a post-doc at Oxford University in  Materials Science. He was awarded the Burger Medal of the American Crystallographic Association in 2011, and the Distinguished Scientist and Burton awards from the Microscopy Society of America. He is a Fellow of Churchill College Cambridge, of the APS and of the IOP in the UK. He was co-editor of Acta Cryst A for a decade, and is the author of texts on high-resolution electron microscopy (4th edition in press) and (with J.M. Zuo) on electron microdiffraction. A Festschrift volume of Ultramicroscopy appeared in 2011. John's lab at ASU has developed new scientific instruments and detectors for electron diffraction and imaging, and, since 2004 hydrated bioparticle delivery devices for X-ray lasers (with B. Doak and U. Weierstall). His current interests are biophysics and diffraction physics for the analysis of XFEL data. John is a member of the DOE's BESAC committee, which oversees research at the six US national laboratories.

Abstract

Since the Linac Coherent Light Source (LCLS) started operation in late 2009 at SLAC we have collected femtosecond pulsed coherent X-ray scattering from many molecular systems. It has been found that sufficiently brief X-ray pulses terminate before radiation damage commences, opening up many opportunities for new experiments in time- resolved imaging with atomic spatial resolution at room temperature, in condensed matter physics, materials science and biology.

I will review some of these, including pump-probe experiments on the large molecular complexes involved in photosynthesis, and on a drug target molecule for sleeping sickness. A new approach to disentangling orientational disorder will also be demonstrated, aimed at reconstructing the image of one molecule, using the scattering from many in random orientations in solution, without modeling, based on angular correlation functions. Prospects for the formation of "molecular movies" which track chemical reactions will be outlined. I'll also describe the new approaches to the phase problem which these experiments suggest. A review of all this work can be found in Spence, Weierstall and Chapman,  Rev Mod Phys 75, 102601 (2012). 

• Professor Christoph Rau, Diamond Light Source, UK

Biography

Professor Christoph Rau studied at the University of Lyon and Technische Universität Berlin, achieving his diploma in physics in 1994. He obtained his PhD at the University of Montpellier in 1999.For the following years he worked as a beamline scientist at the European Synchrotron Radiation Facility in Grenoble.  He moved to the Advanced Photon Source (APS) near Chicago in 2003 and became a visiting assistant Professor at Purdue University. He is associated with Northwestern University Chicago as adjunct assistant Professor since 2007. He started working as Principal Beamline Scientist at Diamond Light Source Ltd. in 2007, being responsible for the I13 Coherence and Imaging beamline project. Since 2010 he is honorary Professor at the University of Manchester.

• Professor Harry Quiney, University of Melbourne, Australia
• Audio recording (mp3)

Biography

Harry Quiney has a background in Theoretical Chemistry (MSc Monash University) and Relativistic Quantum Electrodynamics (D Phil University of Oxford). He was Senior Research Fellow of the Royal Commission for the Exhibition of 1851, EPSRC Advanced Fellow at the Clarendon Laboratory and Lecturer in Chemistry at Wadham College, Oxford. He is currently Deputy Director of the ARC Centre of Excellence for Coherent X-ray Science and Reader in Theoretical Condensed Matter Physics at The University of Melbourne.  Most of his career has been spent investigating relativistic, quantum electrodynamical and weak-interaction effects in atoms and molecules and high-precision spectroscopic tests of physical theories beyond the Standard Model. His current research interests include the design of phase retrieval algorithms for X-ray imaging applications, the fundamental interaction physics of biomolecular imaging using femtosecond XFEL sources and the development of quantum many-body theories.

Abstract

Most phase retrieval algorithms construct an image of a scattering target by propagating a wavefield between a nominal exit surface plane and the detector plane. Implicit in this approach are idealized assumptions regarding the full spatial and temporal coherence of the illumination.  Small deviations from this ideal behaviour may have a significant effect on the quality and achievable resolution of the reconstruction. There are, however,   compelling reasons to employ primary X-ray or VUV sources that do not conform to the ideal coherence model and some significant practical advantages in using partially coherent primary sources, such as synchrotrons,  without first employing a monochromator. Here, we discuss the advantages of Fresnel coherent diffraction imaging using partially coherent sources and present a rather general formulation of diffractive imaging using sources that possess non-ideal spatial and temporal coherence properties. The extension of these  approaches to the study of structural disorder in nanocrystallography and electronic disorder in molecular imaging using femtosecond XFEL sources are also presented.  

• Dr Stefano Marchesini, Lawrence Berkeley National Laboratory, USA
• Audio recording (mp3)

Biography

Stefano Marchesini received his Laurea degree in Physics from University of Parma, Italy in 1996, and his PhD at the University J Fourier of Grenoble, France in 2000 on Fluorescence X-ray holography. He then went to work at Lawrence Berkeley National Laboratory (2000-2002, 2007-present) and Lawrence Livermore National Laboratory (2003-2007), on holography and diffractive imaging techniques using synchrotron and FEL sources.

Abstract

In the past decade, to go beyond hardware fabrication limits in microscopy, groups around the world have started to develop techniques based on the recording of diffraction patterns alone, and subsequent numerical methods to recover an image.

"These lensless techniques are in principle only limited in resolution by the wavelength of the x-rays."  is the premise often found in the literature.

I will describe progress try to fulfill this promise with dirty data and dirty sources using long range and short scale optimization strategies.

• Dr Stephan Hruszkewycz, Argonne National Laboratory, USA
• Audio recording (mp3)

Biography

Stephan Hruszkewycz received his BS in Materials Science and Engineering from The Ohio State University in 2003 and his PhD in Materials Science and Engineering from Johns Hopkins University in 2008.  After completing his PhD thesis which focused on characterizing local and nanometer scale ordering in amorphous metals by experimental and computational techniques, he joined the Synchrotron Radiations Studies group at Argonne National Laboratory in 2008 as a post-doc and became a staff member in 2011.  His current research focuses on developing and using coherent x-ray scattering techniques using state-of-the-art sources to characterize atomic and  nanoscale structure and dynamics in complex materials, most recently with Bragg Projection Ptychography at the Advanced Photon Source and with ultrafast X-ray Correlation Spectroscopy at the Linac Coherent Light Source.

Abstract

X-ray Bragg projection ptychography (BPP) is a robust approach for imaging lattice strain and distortion in thin films by employing coherent diffraction imaging to enhance the structural sensitivity and resolution of nanofocused x-ray scanning diffraction microscopy. Here, we will discuss how 2D coherent Bragg peaks measured with scanning coherent nano-focused x-rays can be phased with standard two-dimensional ptychography algorithms to map lattice features in thin films projected onto a plane.  Two examples will be discussed: 1) an investigation of lattice distortion in the SiGe stressor layer in a prototype SOI device structure, and 2) quantitative nanoscale imaging of local polarization in ferroelectric thin film stripe domains.

• Professor Robert Speller, University College London, UK

Biography

Robert Speller is Head of the Radiation Physics Group at UCL. Originally a cosmic ray astronomer he moved into the application of physics to medical research in the early 1970s. His current research interests cover the applications of novel sensors, scattered radiation fields and imaging techniques in both medicine and security. He has published in excess of 200 papers, holds several patents, is a Fellow of the Royal College of Radiologists (“without examination”) and was recently invited be part of a small committee to advise Government on Olympic security.

• Professor Paola Coan, LMU München, Germany

Biography

Professor Dr Paola Coan got a degree in Physics at the University in Padua (Italy) in 2002 and a PhD in Physics at the Joseph Fourier University in Grenoble (France) in 2006 with a Thesis on the development and application of phase contrast imaging techniques, financed by and performed at the European Synchrotron Radiation Facility (Grenoble). In 2007, she joined, as post doc, the excellence cluster Munich center for Advance Photonics (MAP) at the Ludwig Maximilians University (LMU, Munich, Germany). Since 2009, within the LMU-MAP (Faculty of Medicine and Faculty of Physics) she is leading, as Associate Professor, the research group on brilliant X-Rays for medical diagnostics. She is co-author of more than 30 peer-reviewed scientific papers on phase contrast imaging and medical applications of synchrotron radiation including both theoretical and experimental studies and of as many other publications on the subject.

Abstract

A great ferment has increasingly grown around X-ray phase contrast imaging (PCI) over the past years. This is due to the remarkable improved image contrast and sensitivity provided by PCI against conventional radiology. However, the actual advantage in terms of radiation dose is not clear yet, in particular when whole and large organs are imaged and computed tomography (CT) is performed. Imaging of large (>12 cm) and complex samples remains technically challenging and very little literature exists on this subject. Recent optics and setup developments allowing for the use of 50-100 keV X-rays combined with new low dose CT reconstruction algorithms have considerably increased the potential of PCI-CT. In this talk, the feasibility of low dose, high energy and high resolution PCI-CT and its sensitivity for imaging clinical-like human specimens will be discussed and demonstrated. PCI-CT results of whole human knees and tumour bearing breasts at clinical compatible doses will be shown and compared with clinical images. The image quality and the sensitivity of the technique were qualitatively and quantitatively assessed as very good by radiologists. These results suggest that the PCI-CT technique has the potential of becoming a valuable method in clinical imaging providing a 3D investigation of whole specimens and quasi-histological information of tissues.

• Professor Marco Stampanoni, ETH Zurich, and Paul Scherrer Institut, Switzerland

Biography

Professor Dr Marco Stampanoni studied physics at the Swiss Federal Institute of Technology Zürich (ETHZ) and obtained his MSc in November 998. He enrolled in a PhD program at the Institute for Biomedical Engineering (IBT) at the ETHZ and at the same time, he started a Master of Advanced Studies in Medical Physics, successfully concluded in October 2000. The subject of his physics PhD, defended in 2002, was the development of a novel approach towards X-ray computed tomography at the micron scale. In 2004 he was appointed beamline scientist and initiated the TOMCAT project, a beamline for Tomographic Microscopy and Coherent Radiology experiments at the Swiss Light Source. Stampanoni was appointed Head of the X-ray Tomographic Microscopy Group in 2005 and Assistant Professor (Tenure Track) for X-ray Microscopy at the Department for Information Technology and Electrical Engineering (D-ITET) of ETH Zürich in 2008. He is affiliated with the Institute for Biomedical Engineering (IBT) of the University and ETH Zürich and still heads his team at PSI.

Abstract

High brightness is a fundamental property of third generation synchrotron facilities. Those deliver partially coherent beams, which intrinsically grant access to the phase information from the sample. The Swiss Light Source operates TOMCAT, a beamline dedicated to TOmographic Microscopy and Coherent rAdiology experimenTs. This beamline provides cutting-edge equipment for non-destructive tomographic investigations and offers the necessary instrumentation for phase contrast imaging at spatial resolution ranging over three orders of magnitude as well as the acquisition of 3D volumes within a fraction of a second. In this presentation I will review the main aspects related to dynamical, real-time tomographic microscopy illustrating crucial developments like dedicated detectors, optimized phase retrieval schemes, fast imaging reconstruction algorithms and high-throughput quantification techniques. I will discuss experiments aimed at studying the evolution of complex 3D structures like foams, solidification dynamics of selected metal alloys or the flying mechanism of small insects.

• Dr Peter Cloetens, ESRF, Framce
• Audio recording (mp3)

Biography

Peter Cloetens is research scientist in the X-ray Imaging Group at the ESRF. He received his PhD degree from the Department of Applied Sciences of the University of Brussels (VUB) in 1999. He pioneered propagation based phase contrast X-ray imaging and tomography. His current interests include the methodogies, instrumentation and applications of hard X-ray nanoprobes for quantitative X-ray imaging. He is in charge of the nano-imaging station ID22NI at the ESRF, a high flux nanoprobe for magnified phase contrast imaging and scanning microscopy. His research applications focus on soft condensed matter and biological materials. He is currently project leader of NINA, the ESRF Upgrade beamline for Nano-Imaging and Nano-Analysis. Cloetens received the ESRF Young Scientist Award (1999) and shares the Bessy Innovation Award (2005) and the French national prize "La recherche", human health mention (2008).

Abstract

X-rays are invaluable to obtain the three-dimensional structure of materials on a large range of scales and in a non-destructive manner through tomographic methods.

The multi-modal approach, combining full-field and scanning methods, opens the way to a complete and quantitative characterisation at the nanoscale. Coherent imaging techniques (magnified holotomography and ptychography) can be readily combined with X-ray fluorescence analysis and diffraction on a X-ray nanoprobe.  Phase nano-tomography and nano-laminography are practical methods to zoom non-destructively into the three-dimensional structure of matter. They provide the electron density distribution quantitatively. X-ray fluorescence microscopy provides on the other hand the nano-scale distribution of major, minor and trace elements. Finally, X-ray diffraction gives access to the distribution of the crystalline phases. The combination of full-field and scanning methods provides the 'larger picture' to the slow scanning methods and allows for better quantification and monitoring of radiation damage. These powerful new possibilities are illustrated by applications on biological and energy related materials.

• Dr Robert Bradley, University of Manchester, UK
• Audio recording (mp3)

Biography

Dr Rob Bradley studied for a BA and MSci in Natural Sciences (Physics) at Selwyn College Cambridge University, before gaining a PhD from The University of Manchester in 2006 on fluorescence imaging of tissues. Subsequently, he joined the Wolfson Molecular Imaging Centre at Manchester in a Post-Doctoral position to research image derived input functions for modelling the time dependency of Positron Emission Tomography signals. In 2008, Rob joined Professor Phil Withers' group at the School of Materials as a Research Associate to help set up and provide user support at the Henry Moseley X-ray Imaging Facility. His ongoing research interests are both application and technique based, with particular interest in biomedical applications as well as in nano-scale and phase contrast imaging.

Abstract

Recent advances in x-ray source and detector technology have enabled researchers from a wide range of disciplines to gain insight into the internal structure of samples on the micron to the tens of nanometres scales. However, many objects are weakly absorbing to the hard energy x-rays typically produced by laboratory sources. Instead, these samples can produce significant shifts in the phase of the x-rays, which can be exploited using in-line phase contrast on the micron scale or Zernike phase contrast on the nanometre scale. We present the results of work carried out to optimise phase contrast, and utilise it to extract quantitative information about sample structure for a range of examples.

• Professor Franz Pfeiffer, Technischen Universität München

Biography

After studying physics at Ludwig Maximilian University of Munich, Franz Pfeiffer completed his doctorate at Saarland University, conducting a number of experiments at major research facilities such as DESY in Hamburg. Pfeiffer carried out his post-doctoral research at the University of Illinois before joining the renowned Paul Scherrer Institute in Switzerland. In 2007 he took up an assistant professorship at the ETH Lausanne, and in 2009 he was called to the Chair of Biomedical Physics at the Technical University of Munich, where he is currently establishing a laboratory for biomedical x-ray imaging. Pfeiffer has received many prestigious research award, such as the Leibniz Price of the German Science Foundation and the National Latsis Award of Switzerland.

• Professor John Rodenburg, University of Sheffield, UK
• Audio recording (mp3)

Biography

After obtaining his first degree in Physics at the University of Exeter, John Rodenburg undertook his PhD, a short RA position, and then a Royal Society Research Fellowship at the Cavendish Laboratory, University for Cambridge. In 1999 he moved to a Research Chair at the Material Research Institute (now MERI) at Sheffield Hallam University. Since 2003, he has been based at the University of Sheffield, where he holds a Personal Chair in the Department of Electronic and Electrical Engineering. His early work was on instrument development in electron microscopy, and its application to material science. He also worked on various indirect inverse imaging algorithms. More recently he has invented and developed a number of iterative computational approaches for solving the phase problem in the context of short-wavelength (atomic scale) microscopy. He was the first to demonstrate the method of ptychography at visible-light, X-ray and electron wavelengths: an imaging technique which is now being widely adopted.

Abstract

This talk will try to complement the presentations on X-ray ptychography within the session, describing work on visible-light and electron ptychography. The key benefit of visible-light ptychography arises from the very sensitive and quantitative phase image that can be obtained, say for characterising unstained biological cells and for use in reflection metrology. It is now available as a commercial product for the metrology of contact lenses. On the contrary, electron ptychography remains in its infancy. Unlike photons, electrons are not absorbed, but pass through the object losing energy, consequently adding a background term to the diffracted intensity which varies as a function of the elemental composition and thickness of the object. Many materials of interest are substantially periodic at the atomic scale, so that dynamical scattering is rife even in the very thinnest specimens. Specimen damage is often a very serious issue. Compounding these underlying physical limitations is an array of experimental problems. Scanning the specimen in a controlled way to accomplish the required shifts in ptychography is mechanically very difficult; scanning the illumination leads to changes in the illumination function – undermining the essential assumption of ptychography. Both of these strategies need post processing of the data to infer the actual object/probe positions. Perhaps the most damaging issue of all is the fact that electron sources are far from perfectly spatially coherent. However, electron ptychography must ultimately and uniquely be the route to optimum transmission electron imaging. As in the case of light, perhaps the most important application lies in the phase image, which can replace holography or the complex Zernike phase plates now being developed for whole cell imaging. The talk will also describe some recent developments for accounting for 3D scattering in ptychography.

• Dr Ian McNulty, Argonne National Laboratory, USA
• Audio recording (mp3)

Biography

Dr Ian McNulty received a PhD degree in physics from Stony Brook University in 1991 and joined the Advanced Photon Source at Argonne National Laboratory as an Enrico Fermi Postdoctoral Scholar in June that year. He became a staff physicist at Argonne in 1992 and built the first intermediate-energy x-ray microscopy beamline at APS in 1997. Dr. McNulty subsequently oversaw the development of the APS Sector 2 beamlines and led the APS X-ray Microscopy Group in 2000-2004. Dr. McNulty received the European Union Marie Curie Senior Scientist award in 2005 and University of Chicago Distinguished Performance Award in 2009. Dr McNulty currently leads the X-ray Microscopy Group at the Argonne Center for Nanoscale Materials. His research focuses on ordering in nanomagnetic materials, coherent x-ray imaging, and orbital angular momentum states of light.

• Dr Manuel Guizar-Sicairos, Paul Scherrer Institut, Switzerland
• Audio recording (mp3)

Biography

Originally from Mexico, Manuel received a BSc degree in Physics Engineering in 2002 and MSc in Electronic Systems in 2005 from the Tecnológico de Monterrey, Mexico for work in unstable laser resonators, numerical propagation and non-diffracting beams. He later received a MSc in Optics in 2008 and PhD in Optics in 2010 from the Institute of Optics, University of Rochester in NY, with thesis title “Methods for coherent lensless imaging and x-ray wavefront measurement”. Currently he holds a position of beamline scientist at the cSAXS beamline, Paul Scherrer Institut in Switzerland where he develops methods and analysis techniques for 2D and 3D coherent diffraction imaging, and in particular ptychography.

Abstract

Ptychography is a scanning coherent diffractive imaging technique for which iterative reconstruction algorithms replace imaging lenses. As such, the details of the implemented algorithms play an important role for the quality and reliability of the reconstruction.

In this talk I will discuss advances in reconstruction algorithms and understanding of the signal to noise ratio of information encoding for ptychography. In particular I will address, from first principles to simulations and X-ray data, the impact of the spatial frequency spectrum of the illumination on the object reconstruction and elaborate on strategies for its enhancement.

Furthermore, we will address the implementation of maximum likelihood (ML) optimization as a refinement step for ptychography reconstructions. An approach that combines the robustness and convergence speed of projection based techniques and later refines accounting for the statistical model of detector noise. The latter approach increases repeatibility in the reconstructions, and reduces the integrated flux on the sample that is needed to achieve a given resolution.

• Dr Pierre Thibault, Technical University Munich, Germany
• Audio recording (mp3)

Biography

Pierre Thibault is a junior group leader at the Technische Universität München. He obtained his PhD from Cornell University in 2007 in theoretical physics. As a postdoctoral researcher at the Paul Scherrer Institut (Switzerland), he helped develop high-resolution X-ray imaging techniques, in particular ptychography. In 2011 he was awarded a "starting grant" from the European Research Council to apply and develop further coherent diffractive imaging techniques.

Abstract

Ptychography is an imaging technique that produces quantitative maps of a complex-valued transmission function through the combination of multiple coherent diffraction measurements from the illumination of several overlapping regions on the specimen. Thanks to the information gain provided by the diversity of the measurements, reconstructions from ptychographic data are especially robust in comparison to other X-ray coherent diffractive imaging techniques (CDI). The technique has been extended to three-dimensional imaging and is now used routinely with a few dedicated instruments. This talk will give an overview of recent developments in the fields, from biomedical applications to exensions of the method for partial coherence, dynamical studies, and full-field imaging.