01 March 2016
Lecture Theatre F2, Firth Court
Professor John Rodenburg, Department of Electronic and Electrical Engineering, University of Sheffield.
Ptychography: lens-independent phase-sensitive transmission imaging at visible light, X-ray and electron wavelengths.
Abstract: Ptychography is a computational microscopic imaging technique that inverts diffraction patterns into images. It can be implemented at any wavelength (IR, visible, UV, X-ray, electron) provided a reasonably spatially coherent source is available. It can be undertaken in a completely lensless configuration, although in general a lens can complement the technique, if only used as a radiation condenser. Like holography, ptychography solves the phase problem, but without relying on a reference wave or the need to calibrate the reference wave intensity. Such images have important properties – perfect transfer (all lens aberrations are removed, no Fresnel artefacts, etc.), an extremely sensitive phase image (which can be also be very strong – hundreds of phase wraps), and wavelength-limited resolution. At X-ray and electron wavelengths, removing the requirement of a good quality lens is a major advantage and was the original motivation for the technique. In fact, the fidelity of the phase image is perhaps its key strength, enabling, for example, very high contrast label-free imaging of live cell cultures. X-ray ptychography, and ‘ptycho-tomography’ is now in widespread use at synchrotron facilities around the world. Visible light ptychography is commercially available via a Sheffield University spin-out company. Electron ptychography has encountered more demanding experimental difficulties, but these are now slowly being addressed.