IV. Physical Institute - Ropers group
Ultrafast Dynamics and Nano-Optics
We investigate ultrafast electronic and structural dynamics in condensed matter systems. Employing laser-pump / electron-probe schemes in various configurations and at different energies, we develop and apply new experimental techniques based on imaging with ultrashort electron pulses from nanoscopic cathodes. Our activities include:
- Ultrafast Transmission Electron Microscopy (UTEM)
- Time-resolved Low-Energy Electron Diffraction (ULEED)
- Ultrafast optical spectroscopy.
We study highly nonlinear optical processes in metallic nanostructures. Specific topics include:
- Lensless imaging using high harmonic radiation (HHG)
- Extreme-ultraviolet light generation in plasmonic structures
- Localized photoemission from metal nanotips
- Terahertz and mid-infrared control of nanostructure photoemission.
Nanoscale Magnetic Imaging using High Harmonics
In Science Advances (Dec. 15, 2017), we report on the first realization of magneto-optical microscopy with high-harmonic radiation. Using circularly polarized extreme-ultraviolet harmonics and x-ray magnetic circular dichroism (XMCD), we quantitatively map the magnetization in nanoscale domain patterns. A diffraction-limited spatial resolution below 50 nm is reached in full-field imaging. The work is part of a collaboration of our group with the University of Augsburg, the Technion and the I. Physical Institute.
Attosecond Pulses in the Ultrafast Transmission Electron Microscope
In a recent publication, we demonstrate the generation and characterization of attosecond electron pulse trains in our Ultrafast Transmission Electron Microscope (UTEM). Along the way, we developed a scheme to reconstruct the quantum state of free-electron ensembles in terms of their density matrix. The work was published in Nature Photonics on Nov. 30, 2017.
Ultrafast Low-Energy Electron Diffraction from surfaces
We have developed a new technique to study structural dynamics at surfaces, and used it to study the phase-ordering kinetics after a structural phase transition. The paper was published in Nature Physics on Nov. 6, 2017.