X-ray Crystallography and Imaging

New and extremely brilliant X-ray sources are already in operation and are currently being built on the DESY site in Hamburg. These world class facilities offer new and exciting opportunities in the field of X-ray science. The work of our group aims to exploit and develop new experimental methods to utilize the unique coherence properties of these sources, their timing structure and their micro-focusing capabilities.

In our group we are interested in the development and the application of Coherent X-ray Diffractive Imaging methods for imaging nano-systems such as nano-islands, quantum dots, and biological samples. As we require sources of coherent radiation, we are currently using 3rd generation synchrotron sources and the first XUV Free Electron Laser FLASH here in Hamburg.

X-ray structure determinations normally determine the structure of the electronic ground state of molecules. However, all processes involved in the colorful and living world, for example photosynthesis, proceed via excited states. The time structure of the X-ray beams at 3rd generation synchrotron sources allows one to probe the structure of these excited states that play an important role in biology and chemistry. Current experiments in this field are limited by the high laser power required to excite the samples. Our group is working on a micro-beam approach which addresses this problem.

The new opportunities resulting from these very short X-ray beams of unprecedented flux densities can also cause tremendous damage not only to the sample itself, but also to the X-ray optics used to guide the beam to the sample. In order to design experiments which are not severely affected by radiation damage, and to avoid the introduction of systematic errors due to radiation damage, knowledge of the damage processes is imperative. In our group we address this problem with theoretical modelling of the contributing damage processes. Our predictions are then tested experimentally. This investigation is of special importance for single particle diffraction imaging experiments planned at the free electron laser, where the precise knowledge of radiation tolerance limits is necessary. Experimental work conducted by our group aims to understand radiation damage in biological samples by combining different experimental techniques.

Experiments at new sources also require the development of new hardware to fully utilize their potential. Our focus in this field is the design of instruments of very high mechanical precision.