Ionization dynamics of helium clusters and droplets in intense short-wavelength light pulses

• Applicant: Professor Dr. Thomas Möller
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 260415380

The interaction of intense and ultrashort pulses of short-wavelength radiation with matter has opened exciting research opportunities ranging from atomic and molecular to plasma physics. With the advent of free-electron lasers (FELs) and intense high harmonic (HHG) laser-based sources in the extreme ultraviolet regime (XUV), the field got another strong push since these sources offer great prospects for imaging of ultrafast dynamics with high spatial resolution. The aim of the proposed study is to obtain a detailed understanding of the complex ultrafast ionization dynamics of nanoparticles in intense XUV light pulses on timescales from attoseconds to nanoseconds. Elastic light scattering will be the key experimental method as it allows for taking quasi-instantaneous snapshots of the excitation and dynamics in the particles. Thanks to their simple electronic structure helium clusters, nano- and microdroplets as well as liquid jets will serve as model systems for the proposed work. The seeded FEL FERMI in Trieste, with its small bandwidth and high tunability, offers unique possibilities to perform detailed studies of resonant and non-resonant ionisation processes in He clusters. Based on the successful FERMI experiments of the first funding period, we will continue our program there and extend our studies at the Max-Born-Institute into the attosecond regime, in order to follow the ultrafast dynamics during excitation. We plan to address the ionization processes, nanoplasma formation and the spatial distribution of excitation and charge states. The time-resolved measurements in the femtosecond to nanosecond regime will be performed on single clusters in single shots, thereby overcoming the common limitation due to averaging over different cluster sizes and power densities. At FERMI, we will use our recently developed and tested approach of two-color pump probe diffraction to image the light-induced processes in the clusters. Via selective excitation (i.e. resonant excitation into bound or continuum states) the surface or bulk atoms can be specifically addressed to develop an understanding of resonant/non-resonant diffraction in the cluster. Diffraction imaging with spectrally broad attosecond pulses is going to break new ground. To enter the attosecond regime, we will develop a source for helium microdroplets and liquid jets which will provide sufficient signal even with the shortest pulses. The analysis and modeling of the experimental data will be carried out as before in close collaboration with theory groups, delivering a very detailed picture of the ultrafast excitation, ionization, and electron dynamics in nanoparticles.

• DFG Programme: Research Grants
• International Connection: Switzerland
• Partner Organisation: Schweizerischer Nationalfonds (SNF)
• Cooperation Partner: Professorin Dr. Daniela Rupp