Sheppard, Colin

Colin Sheppard, Professor of Bioengineering and Diagnostic Radiology, National University of Singapore, is visiting the Faculty of Physics and Astronomy as a Carl Zeiss Visiting Professor again in November 2012. During his stay he will give a series of three lectures, starting on November 15th. 


Colin Sheppard moved to the Division of Bioengineering, National University of Singapore, in October 2003. Previously, he has been Professor of Physics (Physical Optics) at the University of Sydney, and University Lecturer in Engineering Science at Oxford University.


Phase space theory of microscopy imaging

Phase space methods are a useful approach to studying signal processing in general, and partially coherent imaging in particular. The physical relevance is that a slowly-varying object has a well-defined instantaneous spatial frequency. The approach leads to a model for imaging in partially coherent bright-field and phase contrast microscopes.
Nov. 15, 2012, 14:00 - 16:00
Lecture Hall, Abbe-Center Beutenberg, Hans-Knöll-Str. 1

Tight focussing of light

There are many instances where we wish to focus light  to the smallest possible spot. Examples are in microscopy, laser micromachining and microprocessing, optical data storage, optical lithography, laser trapping and cooling, physics of light/atom interactions and cavity QED. We all know we need to decrease the wavelength and increase the numerical aperture. But especially at high numerical aperture the polarization of the light becomes very important. The effect on Bessel beams is also discussed.
Nov. 20, 10:00-12:00
Aktionsraum in der Ebene 2, Carl Zeiss AG, Carl-Zeiss-Promenade 10

Pupil filters for improved focusing

In the 1950s, Toraldo di Francia showed that the central lobe of the point spread function can be made arbitrarily small by controlling the amplitude and phase of the lens pupil transmission. In 1990 Popescu and coworkers rediscovered this effect, which is now known as superoscillations. We describe how the performance of these pupil filters can be analyzed in terms of pupil moments, and present various designs of filters. Depth of focus is an important property of the designs. The filters can also be used in confocal systems, with the result that the strength of parasitic sidelobes can be reduced.
Nov. 21, 14:00-16:00
Lecture Hall, Max Wien Platz 1


Previously, Colin Sheppard has been visiting the Faculty of Physics and Astronomy as a Carl Zeiss Visiting Professor in July and August 2011. During his stay he gave a series of three lectures, starting on July 19th. 

Pulsed beams

When a light beam is concentrated in space and time, space-time couplings occur because the wave must satisfy the wave equation. The focused field can be calculated as a summation over the spectral distribution. Gaussian beams and Bessel beams are considered. We find that there are various different assumptions that can be made which lead to different types of pulsed beams. These include "X-waves", "iso-diffracting pulses" and "focus wave modes". We also discuss the effects of nonparaxial beam propagation. The complex-source point approach leads to an elegant and simple model for pulsed beams in terms of pulsed or moving sources.

19.07.2011, 10:00-12:00 Uhr, Abbeanum HS 2

Scattering and imaging

Connections between scattering theory and imaging theory are developed. On the one hand, imaging is found to give a useful interpretation of scattering. But also, scattering gives leads to an understanding of three dimensional image formation. These concepts lead to methods for image reconstruction as a form of inverse scattering.

26.07.2011, 14:00-16:00 Uhr, IPHT-Sitzungssaal

Advances in phase contrast microscopy

Phase contrast microscopy has been an important tool in biomedical imaging for many years. It is noninvasive, in that avoids the need for labeling with a fluorescent or absorbing dye, which can alter the structure or function of the specimen under observation. Phase contrast also needs very low light exposure, thus allowing time lapse studies over extended periods. However, conventional phase contrast techniques suffer from some limitations. Sometimes the resolution is limited, or there are imaging artifacts, and usually the resulting images are qualitative rather than quantitative in nature. An active area of research is therefore the development of techniques for phase imaging that give high resolution, quantitative information. The main techniques that will be discussed are imaging using the transport of intensity equation (TIE), Nomarski differential interference contrast (DIC) and differential phase contrast. All three methods have some strong points that will be compared and contrasted.

02.08.2011, 14:00-16:00 Uhr, IPHT-Sitzungssaal