The overall goal of the HIGH-Q project is to identify strategies for improving the spatial resolution in ultrafast X-ray coherent imaging. The idea is to use very short FEL pulses tuned to excite non-linear effects, which will increase the brightness of single exposure X-ray diffraction patterns of nanoparticles. The brightness is a crucial parameter because currently the spatial resolution in ultrafast X-ray imaging is shot-noise limited in high scattering angles, which carry the information about the finest structures. We have successfully passed two critical steps, which are the corner stones of the entire project. Before the start of the project, we had already demonstrated that transient resonances can make soft X-ray coherent diffraction images brighter and lead to higher spatial resolution in images of Xe nanoparticles. These previous results are currently under review in Nature Communications. I have presented the Xe data and simulation at various international conferences. While the response from my scientific community was mostly positive, a few members were sceptical about the generality of the effect. In particular, it was pointed out that previous studies found that transient resonances in light elements, which are important for organic chemistry and biology, are rather detrimental to the imaging process. Also, the persistence of transient resonances in metals in the hard X-ray regime, which are crucial for high spatial resolution imaging of many samples relevant to chemistry and material sciences, was questioned.
During the course of the HIGH-Q ERC project, we were able to address and refute both concerns. We have demonstrated that (part I a) transient resonances can enhance coherent X-ray diffraction signal from metals in the hard X-ray regime, and that they can enhance the brightness of images of light elements (part I b). Overall, we were able to identify some unexpected difficulties as well as surprising new findings, which will define the next steps of the project as described below. These results have been demonstrated by our group at several international conference and will be used to write future experiment proposals.
The part II of the project focuses on the integration of super-resolution approaches into X-ray coherent diffraction imaging. Our first tests suggest that under certain conditions super-resolution algorithms can provide a better contrast and also a higher spatial resolution. However, in the extreme shot noise limited case, super-resolution approaches can suffer from artefacts, which need to be addressed in the next steps of the project.
