A milestone in coupling THz waves with spin waves that was reached in our lab has been published in Nature Physics (DOI: https://doi.org/10.1038/s41567-022-01908-1). The demonstration experiment showing the spin-orbit torque-mediated transfer of energy from a THz pulse into a spin wave was a collaborative effort: Our colleagues in the HZDR Institute of Ion Beam Physics and Materials Research provided samples and ideas, while the measurements on spin wave generation were conducted using our table-top THz source. You can find additional information in this News & Views article or in the HZDR press release. For this work, Ruslan Salikhov and Sergey Kovalev received the HZDR Research Award.
We published an article about high-field THz science conducted with accelerator-based sources, such as TELBE in the Journal Physik in unserer Zeit (DOI https://doi.org/10.1002/piuz.202201652, in German). In this article we explain how THz radiation can give us an unprecedented insight into the dynamics of low-energy excitations in matter.
November 2022: A new record terahertz third harmonic conversion efficiency was demonstrated in our lab. The corresponding study was just published in the journal Light: Science & Applications (DOI: https://doi.org/10.1038/s41377-022-01008-y). We show that a metamaterial consisting of a topological insulator with gold structures enhancing the incident field reaches a field conversion efficiency of 8%. This important step towards new materials for THz applications was a collaboration with colleagues from the ICN2 in Barcelona and the University of Würzburg.
July 2022: Our study demonstrating THz-slicing as a novel method for synchronizing the TELBE THz pulses with our femtosecond probe laser was published in Optics Express (DOI: https://doi.org/10.1364/OE.454908). This work, titled Terahertz-slicing — an all-optical synchronization for 4th generation light sources, is a collaborative effort with contributions from the group of Prof. Lukas Eng and Dr. Susanne Kehr (TU Dresden). THz slicing is an all-optical and passive mode of synchronization, which reduces the timing jitter at TELBE to ~ 10 fs, enabling real-time lock-in-amplifier demodulation of THz-induced signals. The method enabled the first successful demonstration of a THz s-SNOM in the context of a superradiant THz facility. The article has been highlighted as an Editor's Pick.
May 2022: We published a new study on THz-based diagnostics of ultrashort XUV pulses in Optica (DOI: https://doi.org/10.1364/OPTICA.453130). This THz-ruler for light pulses was developed and demonstrated by large international collaboration of researchers from the DLR institute of Optical Sensor Systems, the TU Berlin, the FU Berlin, the Helmholtz-Zentrum Dresden-Rossendorf, the European XFEL GmbH, the Johannes Gutenberg University Mainz, the University of Aarhus, the Fritz-Haber-Institute, the Max-Planck-Institute for the Structure and Dynamics of Matter, the University of Hamburg and the Elettra Synchrotron Trieste. The method works by quasi instantaneously transforming short-wavelength light pulses into a terahertz light pulse in a specific spintronic metallic multi-nanolayer structure. The information on the pulse properties is encoded in the terahertz waveform and can be detected for each individual laser pulse.
March 2022: New member in the TELBE group. Gulloo Lal Prajapati joined the junior research group of Jan-Christoph Deinert as a postdoc. He brings his expertise in THz spectroscopy of nickelates. At HZDR he will work mainly on the THz-ARPES project. Welcome Gulloo!
March 2022: New experimental capabilities at the superradiant THz facility TELBE: It has been demonstrated that the THz source can operate reliably at a comparably low repetition rate of 10 kHz. This is important for experiments that require highest fields and low residual heating by the THz pulses in parallel. In a first user run, pulse energies of 5 µJ at a frequency of 1.0 THz were reached.
January 2022: A new highly versatile laser system was installed in our lab. This femtosecond system, built by LIGHT CONVERSION, is part of the BMBF project TiNa II, a collaboration with the group of Prof. Lukas M. Eng at TU Dresden. It is destined for terahertz nanoscopy experiments using scanning near-field optical microscopy (THz-SNOM). With its repetition rate of 1 MHz and the ultra-wide wavelength range from 800 nm to 15 µm it will be the starting point for new, groundbreaking experiments at the TELBE facility.
November 2021: In our last beamtime of the year we attempted to use THz driving frequencies > 1.5 THz for the first time in a user beamtime. Thanks to improvements of the electron beam parameters, especially the bunch compression, by the ELBE team, we reached new record THz pulse energies: 6.1 µJ at 1.5 THz and 3.2 µJ at 2.4 THz.
October 2021: We published a new study on THz-driven charge carrier dynamics in topological insulators in NPJ Quantum Materials (DOI: 10.1038/s41535-021-00384-9). Disentangling bulk and surface dynamics in these complex materials is a highly relevant topic and the exact scattering mechanisms and timescales are still under debate. Using different complementary optical techniques, we demonstrate that after THz excitation carriers in the topological surface states relax much faster to their equilibrium state that those in the bulk (see also our press release).
- Our extensive study on THz-driven collective modes in various superconducting materials is available on the arXiv. In this long-term collaboration with Dr. Hao Chu, Prof. Stefan Kaiser et al. we employ the novel method of Higgs spectroscopy to disentangle the intricate interplay of collective modes in cuprate superconductors, identifying a Fano interference between the Higgs mode and charge density wave fluctuations.
- New article published on THz-driven dynamics in superconducting MgB2 in Physical Review B (DOI: 10.1103/PhysRevB.104.L140505) together with our colleagues from Cologne, Beijing and Dortmund.
- Our High power laser system (AMPHOS and White Dwarf from Class 5 Photonics) is installed in our main lab together with its HHG extreme UV source. For the first time, we are able to produce ultrashort XUV pulses for photoelectron emission spectroscopy in the TELBE lab.
April 2021: Our study on THz harmonics from electrically gated graphene layers is published in Science Advances (DOI: 10.1126/sciadv.abf9809). In this study, which is a collaboration with colleagues from Bielefeld, Barcelona and Berlin, we demonstrate how the efficiency of harmonics emission depends strongly on the carrier doping in the graphene layer. To show this we fabricated a device that enables direct tuning of the doping level by applying a small voltage to the graphene layer, as outlined in our press release.
- We welcome our new group member Dr. Thales de Oliveira. Thales has been a long-time colleague working with us on the THz-SNOM as a member of the TU Dresden. After the recent successful implementation of this technique at TELBE (manuscript in preparation) he joined our group full-time to implement and carry out challenging time-resolved THz nanoscopy experiments.
- Our new Coherent Astrella HE USP laser system (9 mJ pulse energy at 1 kHz, 800 nm wavelength) is installed in our new optical lab. We will use this system to generate high-field THz pulses that are complementary to our TELBE sources for various studies on THz-driven dynamics.
January 2021: Our new paper on THz harmonics generation in graphene-based metamaterials are published in ACS nano (DOI: 10.1021/acsnano.0c08106). By using thin metallic stripes as antennas, we show that harmonics emission is greatly enhanced for low driving fields. This approach may provide a viable path towards on-chip THz converters for high-speed optoelectronics, as outlined also in our press release.
September 2020: The results of our experiments demonstrating the inertial dynamics of electron spins driven by intense THz pulses are published in Nature Physics (DOI: 10.1038/s41567-020-01040-y). In a collaboration with Prof. Stefano Bonetti and other colleagues we were able to show that, by using the intense THz pulses from the TELBE source, the excited spins not only exhibit precessional motion, but also start to nutate. Why knowledge about these intricate spin dynamics may help in the development of new ultrafast and efficient data storage devices can be read in our press release.
- We have developed and implemented a novel method for measuring ultrafast laser-induced magnetization dynamics by transient THz emission spectroscopy. This technique for studying magnetic phase transitions is complementary to techniques based on the magneto-optic Kerr effect or X-ray magnetic circular dichroism. Our findings are published in Applied Physics Letters (DOI: 10.1063/5.0019663).
May 2020: Publication of new article on terahertz high harmonic generation in the Weyl semimetal Cd3As2 in Nature Communications (DOI: 10.1038/s41467-020-16133-8). For more details on how we use high-field THz pulses to drive carriers in this Dirac materials into the nonlinear regime, see our press release.
April 2020: New article on Higgs spectroscopy published together with our colleagues from Max Planck Institute for Solid State Research (MPI-FKF) and University of Tokyo in Nature Communications (DOI: 10.1038/s41467-020-15613-1). An overview of this newly developed technique that reveals the complex interactions of collective oscillations in superconductors can be found in our press release.