Speaker: Professor John Rodenburg, Department of Electronic and Electrical Engineering, University of Sheffield
Date:Wednesday 16th December
Time: 2pm
Venue: LT/B B46
Abstract:
In the field of short-wavelength atomic-scale imaging (high-energy electrons and hard X-rays), it is extremely difficult and costly to manufacture good quality lenses. Even the best electron aberration-corrected lens (typical price £500k) can only process the scattered electron wave up to a semi-angle of about 3 degrees. In an attempt to overcome these limitations, we have developed a computational method of imaging without lenses at all, by solving for the phase of diffraction patterns. Although the phase problem has been shown to be tractable if certain a-priori knowledge about the object is given (e.g. that it is of limited size), existing algorithms require very large computing resources and are plagued by multiple solutions. Our new method can image wide fields of view, obtaining good computational reconstructions in seconds. We have found that there are significant applications for the technique in visible-light optics. Working distances can be very large (5 cm) without appreciably limiting resolution and without the cost of a good-quality objective lens. Focussing of the image can occur after data collection and the absolute phase images available are much easier to process (say for screening abnormal cell shapes) relative to conventional phase-sensitive imaging techniques (e.g. Zernike or differential phase constrast imaging). The talk will also briefly cover recent progress in experimental electron and X-ray diffractive imaging.