Ionization and Relaxation Dynamics of Hydrogen Nanoplasmas: Compiling the full picture

• Applicant: Privatdozent Josef Tiggesbäumker, Ph.D.
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas ; Experimental Condensed Matter Physics
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 498124039

The experimental project aims to comprehensively resolve the temporal and spatialelectron and ion dynamics of exploding hydrogen nanodroplets including their mutual link upon exposure to strong optical laser fields. With respect to our recent work on nanoplasma dynamics of atomic helium, the molecular target composition is a new aspect which could even be relevant for applications like pulsed neutron sources and proton acceleration. An objective will thus to resolve the contributions of H and H$_2$ in the different phases of the plasma development with the help of time-resolved spectroscopy. The focus of the studies on ultrafast dynamics and plasma relaxation are (i) the role of collective and coherent effects on energy absorption, ion charging and electron acceleration, (ii) electron-ion recombination and subsequent correlated decay in the late plasma period. Due to characteristic signatures in the electron emission, time-resolved spectroscopy enables to resolve the development of the plasma potential in the final phase in real time using two newly developed diagnostic methods, i.e. impeded Auger emission and transient above threshold ionization.The far-reaching objectives of the project will in the first stage be achieved by adjusting the initial properties via target preparation (droplet size, impurity doping) and laser conditions, which allows us to implement a variety of nanoplasma conditions. The scenarios range from quasi-neutral to fully ionized nanoplasmas and includes a pump-probe setup to optimize the charging process. Diagnostics are used, which allow to determine charge state resolved ion recoil energies and record angular-resolved electron spectra. Further, the application of the pump-probe technique provides a characterization of the Coulomb explosion and, using two-color laser fields and phase-sensitive spectroscopy, an attosecond-resolved analysis of the electron dynamics at all periods of the nanoplasma, i.e. from the femtosecond to the nanosecond time scale. Finally, a comprehensive picture of the Coulomb explosion of hydrogen nanodroplets will be obtained. In addition, the project closes the gap between attosecond experiments on atoms, molecules and plasmas.

• DFG Programme: Research Grants