Research

Short-wavelength FELs open new directions for exploring the structure and ultrafast dynamics of complex systems [1]. Main objectives are high-resolution structural and dynamical imaging of nanoparticles, macromolecules or viruses. Clusters and nanodroplets provide the perfect platform to develop a fundamental understanding how to extract various types of structures and complex dynamics, including the imaging of ultrafast electronic processes and transient states of matter in a single nanoparticle. Exposing single nanoparticles to the high photon fluxes required for single-shot diffractive imaging typically converts them into a plasma-like state, which is followed by various relaxation processes with signature behaviors such as absorption enhancement, bleaching, or suppression of electron emission. Especially interesting is the case of resonant excitation when numerous atoms within the same particle are excited simultaneously. It has been found that an efficient and extremely fast (fs-ps) interatomic Coulombic decay (ICD) [2], and collective auto-ionization [3] can drastically change the nanoplasma formation and dynamic.
Recently, diffraction patterns of single He nanodroplets were recorded at FERMI.  As size and shape differs from droplet to droplet (see Fig. 4), exploring the static and dynamic properties of individual droplets is experimentally challenging. Deformed droplets tilted out of the scattering plane produce features in the wide-angle diffraction pattern that break the point symmetry. When compared to a numerical model of non-superfluid rotating drops, experimental data show unexpectedly good agreement, considering that superfluidity and the formation of vortices in He nanodroplets with high angular momentum have been previously observed [4].
 

[1] T. Fennel, et al., Rev. Mod. Phys.82, 1793 (2010).
[2] A. C. LaForge et al. Sci. Reports 4, 3621 (2014).
[3] Y. Ovcharenko et al. Phys. Rev. Lett. 112, 073401 (2014).
[4] L. F. Gomez, Science 345, 906 (2014).