Phase modulation technology for X-ray imaging

We plan to develop coherence-based X-ray imaging methods, which have great potential for solving a wide range of physical problems and are expected to see wide usership, especially at Diamond's I13 beamline. Coherence is a relatively new addition to the capabilities of synchrotron facilities and not all of its applications have been explored. There is much to learn by transferring technology from existing visible-light capabilities, as we plan. Gratings for X-rays, which need high aspect ratio and small (50-nanometer) feature sizes, can be manufactured on site at Harwell. Grating-based measurement techniques are in the early stages of development and will be developed under this proposal for the benefit of the materials and biological imaging communities.Microfabrication has always played an important role in modern x-ray imaging. From the 1952 proposal by Albert Baez to use Fresnel zone plates to build an x-ray microscope, x-ray imagers have profited from the rapid advances in the microfabrication industry. X-ray zone plates are now the key technology for x-ray microscopes. The modern practice of making them by electron-beam writing was pioneered by the MIT and IBM groups in the early eighties and can now deliver soft X-ray zone plates with an outer zone width (which roughly equals the resolution) of 10 to 15 nm. Other types of microfabricated objects, such as resolution test patterns, Zernike phase rings, uniformly redundant arrays, and the list continues to grow. Diamond's I-13 beamline is a world-class facility which can provide the highly coherent beams needed to advance the technology. Its two branches correspond to the two basic modes of imaging, in real and reciprocal space, which will provide the baseline capabilities:i) X-ray computed tomography (CT) for 3D volume imaging with amplitude or phase contrast. A rotational series of projection views is assembled into a 3D image using computation. ii) Coherent Diffraction Imaging (CDI) by phasing and subsequent inversion of diffraction patterns, either in the forward direction or around Bragg peaks from a crystalline sample. CDI, however, does require a computational phasing step, for which good algorithms are available now and better ones are under active development.On a longer time scale, the proposed methods development will interface with Diamond beamline B-24, for cryogenic Transmission X-ray Microscopy (TXM). This project needs the highest possible quality Fresnel Zone Plates operating in the water window , which could be achieved with a well-planned upgrade pathway for the Harwell microfabrication facility. Since x-ray imaging programs are totally dependent on the fabricators of these items, it is vital that routine access to the fabrication facilities should be available to UK researchers, preferably within the UK, and preferably within STFC. Having a dedicated full-time person in place working on X-ray optics within this project will be a first step in this direction.The research enabled by the new methods we will develop will see wide application in visualising the details of processes involved in biological, medical and materials science. The flexibility of the methods we will develop will also enable undertaking dynamical studies of similar processes, as well as the imaging of samples requiring sophisticated manipulation, housing and/or extreme pressure/temperature conditions. Our project has very broad scope, ranging from nanoscale structures accessible only though diffraction (CDI) to macroscale whole animal studies, necessarily requiring a large field of view. All these X-ray imaging modalities are seeing rapid growth at the present time. This project focuses on enhancements achievable by phase modulation, either by improving image contrast or by broadening the range of accessible samples by allowing them to imaged (phased) in the first place.