The Pi-Phi Consortium is funded by the Engineering and Physical Science Research Council (EPSRC) Basic Technology programme to investigate and exploit the novel imaging capabilities of a method called ptychography over visible light, X-ray and electron wavelengths.

Like holography, ptychography measures the phase and amplitude of a scattered wavefield. Unlike holography, it does not require a reference wave – the object itself acts as its own diffracting reference. An area of illumination (which can be formed either by a simple aperture upstream of the object, or by a lens) is moved over the object while a series of either Fraunhofer of Fresnel diffraction patterns are recorded.  Each diffraction pattern is obtained from an area of the specimen which overlaps with another area of specimen previously illuminated, thus introducing a large degree of redundancy in the data: this is used to solve the phase problem (i.e. to calculate the phase of the diffraction patterns which can only be measured in intensity). This roundabout lensless method creates aberration-free very high contrast absolute phase images (less than 0.02 radian sensitivity) at a resolution determined by the effective numerical aperture dictated by the angle subtended by the detector at the object plane.
 
Ptychography does not require a lens.  It therefore has huge potential to revolutionise electron and X-ray imaging where the manufacture of good quality lenses of high numerical aperture (i.e. high resolution) is difficult or expensive.

The Consortium brings together leading researchers in the field of imaging from the Universities of Sheffield (lead), Cambridge, Lincoln, Oxford, University College London, King's College London, Manchester Metropolitan and the Science and Technologies Facilities Council.