Throughout the last years, the interaction of intense, short-wavelength light pulses with matter has evolved into a vivid, interdisciplinary research field. Thanks to their very short pulse duration, pulses from x-ray free-electron lasers can be focused to extreme power densities. Combined with the light’s short wavelength, this enables a unique application: the imaging of individual nanoparticles and macromolecules. For this method, the light exposure time needs to be short enough to outrun most of the inevitable destruction of the probe, and the achievable resolution power critically depends on the details of the destruction process. Thus, developing a fundamental understanding of the light induced dynamics is of key interest.
Daniela Rupp is awarded the Karl-Scheel-Prize 2018
Two novel experimental methods realized by Daniela Rupp and her colleagues are particularly worth mentioning. One approach yields a solution for a fundamental problem connected to imaging of nanoparticle dynamics. Usually, nanoparticles show a variation in sizes and shapes, but the conventional way of pump-probe imaging only yields an image of an evolved stage while the particles initial state remains undetermined. Daniela Rupp’s team set up an apparatus splitting and delaying a short-wavelength light beam such that two separate detectors could record images of both the initial particle and, at a certain time delay, of the light-induced changes. By measuring image pairs at different time delays and sorting them for identical initial images, even a movie can be created.
Furthermore, until recently imaging of single free nanoparticles had been restricted to free-electron laser facilities. In an international collaboration led by Daniela Rupp this approach was brought into the lab for the first time. By choosing appropriate parameters and using helium nanodroplets as a target system the team succeeded in both pioneering a technology and uncovering a very interesting scientific result. They could show that the shapes of rapidly rotating droplets, instead of taking on an oblate, wheel-shaped form, as published by an American group in Science, form cigar-like, prolate shapes. The proof-of-principle experiment promises to open novel research fields at laser-based high-harmonic generation sources deliver weaker but shorter pulses than FELs, down into the attosecond regime. Entering this time scale may even allow for diffractive imaging of electron motion, making this pioneering experiment the basis of Daniela Rupp’s Leibniz grant for a junior research group at the Max-Born Institute.