Instrument for spatiotemporally-resolved magneto-optical measurements

• Subject Area: Condensed Matter Physics
• Term: Funded in 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 555969654

Ultrafast measurements are a powerful tool in experimental physics. They make it possible to uncover fundamental physical principles by measuring fundamental time scales of processes. By using pulsed X-ray light, ultrafast measurements can be combined with a spatial resolution in the nanometer range. The resulting videos provide unique insights into collective dynamics of the nano-cosmos, such as the quasiparticle dynamics of magnetic skyrmions, which our group has successfully imaged. Until now, however, such experiments were limited to large-scale research facilities such as synchrotrons and free-electron lasers. Our proposal is based on a recent breakthrough in the development of XUV laboratory sources (so-called "High Harmonic Generation (HHG)" sources), with which magnetic imaging with 16 nm spatial resolution and sub-35 fs time resolution could be realized in the laboratory. With these HHG sources, extreme ultraviolet (XUV) radiation is generated in the form of high harmonics (HHG) in a noble gas medium from femtosecond laser radiation. Like the driving laser, the XUV radiation is coherent, which allows imaging via coherent imaging techniques. These imaging techniques are being developed by our group, among others. The device applied for here is intended to enable precisely this type of time-resolved coherent magnetic imaging in a HHG branch of the instrument. In a second branch, time-resolved magneto-optical measurements are carried out in the visible range via the magneto-optical Kerr effect (TR-MOKE) without spatial resolution. On the one hand, this TR-MOKE branch expands the possible sample environments, as measurements can be carried out in air. On the other hand, it allows access to complementary interband spectroscopic information. The core element of the system is a femtosecond laser which, with 3 mJ pulse energy and sub-35 fs pulse duration, is able to generate coherent and circularly polarized XUV radiation with a photon energy between 50 eV and 150 eV in the HHG branch and is simultaneously available as a pump and measurement beam for the TR-MOKE branch. We plan to use this device to investigate nanometer-scale magnetic textures (e.g. skyrmions and domain walls) and their response to strong excitations such as optical pulses or strong current pulses, thus establishing research in the laboratory that was previously only possible at free-electron lasers. The device will also be used to develop coherent imaging methods.

• DFG Programme: Major Research Instrumentation
• Major Instrumentation: Anlage für orts- und zeitaufgelöste magneto-optische Messungen
• Instrumentation Group: 5700 Festkörper-Laser
• Applicant Institution: Universität Augsburg
• Leader: Professor Dr. Felix Büttner