High-field THz-driven phenomena group
(THz @ ELBE)
THz based electron
The High-field THz-driven Phenomena group is performing different ultra-fast spectroscopic techniques with few femtosecond time resolution to investigate dynamics in matter driven by high-field THz pulses. The specific interest is to understand how matter can be controlled and/or manipulated in the electronic ground state by the transient electric and magnetic fields of intense (THz) photon pulses. For that purpose, the group operates several state-of-the-art laser-driven high-field THz sources and performes research on accelerator-based high-field THz and fs - X-ray source world-wide. The group is furthermore responsible for the development of the scientific programm of, the operation of as well as the user support and the inhouse-research at the currently commissioned High-field High-Repetition-Rate THz user facility TELBE.
TELBE already since 2014 serves as the Accelerator Research and Development (ARD) test facility for electron bunch diagnostic on quasi - cw low energy electron beams with in the "ARD subtopic III: fs-ps electron and photon beams" of the Helmholtz-research Association a topic of high relevance for the operation of quasi-cw linac driven large scale facilities such as LCLSII. Femtosecond level THz based electron bunch diagnostic is hence a second focus of the groups specific scientific interests.
- 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.
- 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!
- 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.
- 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.
- 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.
- 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.
Within the so called THz photondiagnostic collaboration (THODIAC), we collaborate intensively with colleagues at DESY (source development, electron bunch diagnostic, user experiments),CFEL, FUB, MBI and FHI (Pilot THz pump probe experiments), XFEL, HZB, DLR, TUD and the PTB (electron bunch diagnostics and THz photondiagnostic). Additionally the activities are supported by currently two BMBF projects: Spektrale Analyse und ortsaufgelöstes Monitoring von Elektronenpaketen durch THz-Strahlung (SAMoS) and Transient Nanoscopy in the deep Terahertz Range (TiNa) as well as two projects funded by the European Union: European Cluster of Advanced Laser Lightsources (EUCALL) and Terahertz RAdio communication using high ANistropy SPIn-torque REsonators (TRANSPIRE).The activities are furthermore are an essential part of the HZDRs participation in the HGF program topic Accelerator Research and Development (ARD). In case of questions concerning the ARD-ST3 test facility, TELBE or specific potential ARD or high-field THz experiments please contact S. Kovalev or J.-C. Deinert.
Helmholtz Research Association:
- Program topics:
- Helmholtz-Excellence Network: Physics of Life (PoL)
- Integriertes Spektrometer zur Elektronenbunchform-Onlinediagnose (INSel)
- Spektrale Analyse und ortsaufgelöstes Monitoring von Elektronenpaketen durch THz-Strahlung (SAMoS)
- Time-resolved Nanoscopy in the deep THz regime (TiNa)