A series of tutorial-level lectures

Coherent X-rays and their Applications

A Series of tutorial-level lectures edited by Malcolm Howells,

ESRF Experiments Division

 Mondays, 5:00 pm in the Auditorium (except where otherwise stated)

7 April 2008,  Malcolm Howells - 5:30 pm!

Coherent x-rays: overview
Introduction, books and references, history, present-day coherence experiments, what is coherence? What is coherent optics? The diffraction integral, optical propagators, summary of the remaining nine talks, come to this one to see if you want to come to the others.

21 April 2008, Malcolm Howells - CTRM room!

Coherence theory applied to X-ray beam lines
Development of coherence ideas with visible light, mathematical description, experimental meaning. Undulators, the one-electron pattern, definition of a mode phase space, the degeneracy parameter, statistics and modeling of a synchrotron light source, depth of field effects, propagation of coherence, partially coherent diffraction, why do nearly all synchrotron beams have horizontal stripes?

28 April 2008,  Anatoli Snigirev

Optical components for coherent X-ray beams
Definition of the coherence requirements on mirrors, crystals and windows, how close are we to meeting them? Consequences of failing to meet requirements, strategies for improvement, what remains to be done? What new challenges do the “purple-book” experiments pose for optics? Single-bounce single-capillary reflectors versus compound refractive lenses.

26 May 2008, Malcolm Howells - CTRM room!

Coherence properties of synchrotron light sources: application to x-ray microscopes
Introduction to x-ray microscopes at synchrotrons, zone plates, transmission x-ray microscopes (TXMs) and scanning transmission x-ray microscopes (STXMs), sample illumination (condenser) systems, should the illumination be coherent, is the image coherent? Role of beam angle in determining resolution, Fourier optics treatment, contrast transfer, reciprocity, influence of coherence on resolution, coherence and Zernike phase contrast, Wigner phase contrast, are microscopes flux or a brightness experiments? Some example results.

Further information (restricted access):
"Theory of the production of the Fourier transform of an object in planes other than the back focal plane of a lens"
"The properties of Undulator Radiation" & correction
"Principles and Application of Zone Plate X-ray Microscopes"

2 June 2008, Peter Cloetens - Room 500 !

Coherence activities at the ESRF: phase-contrast x-ray imaging in two and three dimensions
Propagation-based phase-contrast imaging, coherence conditions, the forward problem; Fresnel diffraction, the inverse problem; phase retrieval.  Three-dimensional imaging; holography and holotomography, projection microscopy.

9 June 2008, Jean Susini

Coherence activities at the ESRF: Scanning transmission x-ray microscopy
The zone-plate scanning transition x-ray microscope (STXM), special capabilities, magnification, radiation damage, spectromicroscopy, energy tuning, use of multi-keV x-rays, the maturity of the field.  Technical assessments of zone plates compared to Kirkpatrick-Baez systems and of high-beta versus low-beta sources, the use of secondary sources.

23 June 2008, Malcolm Howells

Principles and Practice of coherent X-ray Diffraction Imaging
The basic idea: measure the intensities, compute the phases, why the need for coherence? Schematic experiment, schematic algorithms, oversampling: is it necessary? History, active groups and their achievements, experimental realities and limitations, computational challenges, radiation damage limitations, resolution-flux scaling, ways around the damage limit? Alternative schemes – ptychography

30 June 2008, Anders Madsen

X-ray photon correlation spectroscopy
Temporal and statistical analysis of speckle diffraction patterns from disordered samples. Correlation functions. The beamline setup, optics, detectors,.... 2d XPCS, ergodic/non-ergodic samples, examples of equilibrium/non-equilibrium dynamics. XPCS History, XPCS worldwide, complementary methods. XPCS at a XFEL?

9 July 2008, Malcolm Howells - Room 500

Is there a role for coherent X-rays in biological structure determination ?

In this presentation we review the meaning of coherence and its practical realization in present-day synchrotron x-ray sources.  We define x-ray coherence quantitatively in terms of the phase-space concept and use this to show how different measurement tasks in crystallography and other fields can be matched to beams of an appropriate degree of partial or full coherence. 

Coherent x-rays are already being used for imaging experiments on non-periodic samples and high-resolution (10 nm) three-dimensional images have been produced.We review the principles, history and current practice of this technique known as coherent x-ray diffraction imaging (CXDI).Although CXDI has not so far produced a high-resolution three-dimensional image of a frozen-hydrated biological sample, this is the goal of much current development work and we report on progress.

Radiation damage is often an issue in biological imaging and we report results of calculations that show where the damage limit to resolution is likely to be for simple CXDI of natural biological material.We suggest that the damage limit may be circumvented in some interesting special cases by the use of prior knowledge and suggest some experimental approaches.

Finally we report on two further techniques that have been conceived to circumvent damage in x-ray imaging: (i) The “diffraction before destruction” approach in which a fast free-electron-laser x-ray pulse is used and (ii) the so-called “serial crystallography” in which the molecules in a molecular beam are oriented by elliptically-polarized laser light before being imaged by CXDI methods.Both these schemes have been the subject of much study and some important steps have been made experimentally.Nevertheless, the fruits of these projects have to be regarded as some years away.