T4: Collective and correlated electron dynamics at the nanoscale

We combine the ultrashort pulse duration with the high photon energy provided by FEL and HHG sources to investigate both collective and correlated electron dynamics in nanoparticles using coherent diffractive imaging (CDI) and time-resolved photoelectron and photoion spectroscopy. We aim to spatially resolve at the nanoscale ultrafast electron dynamics in relatively large nanoparticles. In addition, we are developping a source of ultrashort electron pulses for ultrafast electron diffractive (UED) experiments at high repetition rate to image the transient structure of photoexcited molecules.

Coherent diffractive imaging of individual free-flying nanoparticles

Single-particle diffraction images contain information on the particle’s structure and ultrafast electron dynamics.

Two-color XUV diffraction image of a helium nanodroplet measured at the FERMI free electron laser.

Daniela Rupp, Thomas Fennel, Arnaud Rouzée, Linos Hecht, Katharina Kolatzki, Nils Monserud, Mario Sauppe, Bernd Schütte, Björn Senfftleben, Rico Tanyag, Julian Zimmermann

In this topic, we study the structure and dynamics of single nanoparticles in free flight with coherent diffractive imaging, aiming especially at resolving ultrafast electron dynamics in space and time. Therefore, we employ intense and short XUV pulses from free-electron lasers (FELs) and high harmonic generation sources to measure coherent diffraction images from single nanoparticles and droplets in free flight. The nanoparticle’s structure can be determined from the diffraction images. Even three-dimensional structural information is contained in wide-angle diffraction images obtained in the XUV regime and can be retrieved with forward-fitting procedures. Building on the understanding of the particle’s structure, we are developing and employing novel experimental and analysis approaches based on multicolor-XUV pulses to visualize and trace the (sub-) femtosecond dynamics of the nanoparticle’s electronic structure via the diffraction images.

Multiphoton ionization dynamics of atoms and clusters by intense XUV pulses

5 m long, high flux high harmonic beamline

Velocity map imaging spectrometer for XUV multiphoton ionization experiments

Bernd Schütte, Thomas Fennel, Arnaud Rouzée

Using intense HHG pulses, we investigate the ionization and relaxation dynamics taking place in van-der-Waals bound dimers and large clusters. The few-femtosecond charging dynamics of extended clusters are mapped using terahertz streaking. XUV-NIR pump-probe schemes are employed to study the electron-ion recombination dynamics as well as the correlated electronic decay (CED) processes that take place in the confined nanoplasma that is formed. Our intense attosecond and femtosecond XUV sources allow us to observe and understand complex processes evolving in these systems on the fastest timescales.

Ultrafast electron diffraction

Electron diffraction patterns of gold (100) 100-nm crystalline (bottom left) and aluminium polycrystalline thin films (bottom right) measured with the new 100 kHz ultrafast electron diffraction set-up.

Kasra Amini, Mark Meroe and Fernando Rodriguez Diaz

In this topic, we image the nuclear and lattice structure and dynamics of gas-phase molecules and solid-state samples using a non-relativistic 100-keV ultrafast electron diffraction (UED) set-up operating at 100-kHz. The structure of the target sample can be directly retrieved from the measured diffraction patterns with sub-atomic picometer spatial resolution. The time-resolved dynamics of a photo-induced chemical reaction can be followed in real-time by operating our UED set-up in an optical-pump electron-probe configuration, with multiple time-resolved snapshots measured at various pump-probe delays to obtain a “molecular movie” of the ensuing dynamics. Our UED set-up is driven by a home-built 250-W, sub-70-fs, 100-kHz OPCPA laser system that enables UED measurements at a significantly higher repetition rate (100-kHz) than current state-of-the-art non-relativistic <100-keV (<5-kHz) and relativistic 3.7-MeV (<0.36-kHz) gas-phase UED set-ups. The higher repetition enables the use of fewer electrons in each electron bunch (<1E3 electrons) to minimise the space-charge temporal broadening experienced in UED set-ups operating with a large bunch charge (>1E4 electrons), leading to a much lower electron pulse duration. In such a 100-kHz UED setup, we anticipate the measurement of photo induced dynamics with picometer and sub-100-fs spatiotemporal resolution, which will be significantly beyond the current state-of-the-art in gas-phase UED.