A5076525642- Particle Accelerators and Free-Electron Lasers
- Terahertz technology and applications
- Gyrotron and Vacuum Electronics Research
- Advanced X-ray Imaging Techniques
- Particle accelerators and beam dynamics
- Laser-Matter Interactions and Applications
- Photonic and Optical Devices
- Magnetic properties of thin films
- Physics of Superconductivity and Magnetism
- Superconducting and THz Device Technology
- Advanced Chemical Physics Studies
- Molecular Junctions and Nanostructures
- Laser-Plasma Interactions and Diagnostics
- Spectroscopy and Quantum Chemical Studies
- Spectroscopy and Laser Applications
- Laser-induced spectroscopy and plasma
- Atomic and Molecular Physics
- Mass Spectrometry Techniques and Applications
- Magnetic and transport properties of perovskites and related materials
- Spectroscopy Techniques in Biomedical and Chemical Research
- Superconducting Materials and Applications
- Plasmonic and Surface Plasmon Research
- Surface and Thin Film Phenomena
- Planetary Science and Exploration
- Advanced Condensed Matter Physics
Technische Universität Berlin
2000-2024
Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)
2019-2024
Instituto de Óptica "Daza de Valdés"
2024
Sensor Electronics (United States)
2024
Optica
2024
Sensors (United States)
2023
Weatherford College
2022
Stockholm University
2021
Helmholtz-Zentrum Dresden-Rossendorf
2011-2020
Deutsches Elektronen-Synchrotron DESY
2007-2017
Science and technologies based on terahertz frequency electromagnetic radiation (100 GHz–30 THz) have developed rapidly over the last 30 years. For most of 20th Century, radiation, then referred to as sub-millimeter wave or far-infrared was mainly utilized by astronomers some spectroscopists. Following development laser time-domain spectroscopy in 1980s 1990s field THz science technology expanded rapidly, extent that it now touches many areas from fundamental 'real world' applications....
FLASH, the Free-electron LASer in Hamburg, is a worldwide unique source for extremely bright ultra-short laser-like pulses tunable wide spectral range extreme ultraviolet and soft x-ray region (Ackermann et al 2007 Nat. Photonics 1 336–42). To fully exploit features of this new generation light sources, user facility with efficient radiation transport to experimental area novel online photon diagnostics capable characterizing parameters FLASH has been built. It serves broad community active...
We report on terahertz spectroscopy of quantum spin dynamics in α-RuCl_{3}, a system proximate to the Kitaev honeycomb model, as function temperature and magnetic field. follow evolution an extended continuum below structural phase transition at T_{s2}=62 K. With onset long-range order T_{N}=6.5 K, spectral weight is transferred well-defined excitation ℏω_{1}=2.48 meV, which accompanied by higher-energy band ℏω_{2}=6.48 meV. Both excitations soften field, signaling close B_{c}=7 T, where...
Abstract Ultrashort flashes of THz light with low photon energies a few meV, but strong electric or magnetic field transients have recently been employed to prepare various fascinating nonequilibrium states in matter. Here we present new class sources based on superradiant enhancement radiation from relativistic electron bunches compact accelerator that believe will revolutionize experiments this field. Our prototype source generates high-field pulses at unprecedented quasi-continuous-wave...
Abstract Graphene has long been predicted to show exceptional nonlinear optical properties, especially in the technologically important terahertz (THz) frequency range. Recent experiments have shown that this atomically thin material indeed exhibits possibly largest coefficients of any known date, paving way for practical graphene‐based applications ultrafast (opto‐)electronics operating at THz rates. Here advances booming field optics graphene are reported, and state‐of‐the‐art...
Ultrafast heating of a ferrimagnet’s crystal lattice leads to new state matter with hot spins yet unchanged magnetization.
Abstract In high-energy physics, the Higgs field couples to gauge bosons and fermions gives mass their elementary excitations. Experimentally, such couplings can be inferred from decay product of boson, i.e., scalar (amplitude) excitation field. superconductors, Cooper pairs bear a close analogy Interaction between other degrees freedom provides dissipation channels for amplitude mode, which may reveal important information about microscopic pairing mechanism. To this end, we investigate...
Nonlinear optics is an increasingly important field for scientific and technological applications, owing to its relevance potential optical optoelectronic technologies. Currently, there active search suitable nonlinear material systems with efficient conversion a small footprint. Ideally, the system should allow chip integration room-temperature operation. Two-dimensional materials are highly interesting in this regard. Particularly promising graphene, which has demonstrated exceptionally...
We turn graphene from an inert electronic material to the most nonlinear for terahertz range using a small voltage.
Recoil-ion momentum distributions for two-photon double ionization of He and Ne (variant Planck's over omega=44 eV) have been recorded with a reaction microscope at FLASH (the free-electron laser Hamburg) an intensity approximately 1 x 10(14) W/cm2 exploring the dynamics two fundamental two-photon-two-electron pathways, namely, sequential direct (or nonsequential) absorption photons. We find strong differences in recoil-ion patterns mechanisms pointing to significantly different two-electron...
We used ultrafast resonant soft x-ray diffraction to probe the picosecond dynamics of spin and orbital order in ${\mathrm{La}}_{0.5}{\mathrm{Sr}}_{1.5}{\mathrm{MnO}}_{4}$ after photoexcitation with a femtosecond pulse 1.5 eV radiation. Complete melting antiferromagnetic is evidenced by disappearance $(\frac{1}{4},\frac{1}{4},\frac{1}{2})$ peak. On other hand, $(\frac{1}{4},\frac{1}{4},0)$ peak, reflecting order, only partially reduced. interpret results as evidence destabilization...
We present kinematically complete data on two-photon double ionization of Ne induced by short (∼25 fs) intense (∼5 × 1013 W cm−2) free-electron laser pulses at 44 eV. The observed electron energy spectrum points to the dominance 'sequential' ionization. analyse state-selective angular distributions as well two-electron correlation function, and suggest a method determine time delay between both steps. measured asymmetry (-) parameters significantly deviate from results an earlier...
The irradiation-induced reduction of electrochemically grafted nitrobenzene films on Si(111) was monitored by high-resolution photoelectron spectroscopy. experiments were performed using synchrotron soft X-ray irradiation at the BESSY II facility. evolution different chemical species as a function time. Careful fitting Si2p, C1s, N1s, and O1s core level spectra allowed us to follow this process in detail determine constants growth decay specific components. changes caused secondary electron...
Understanding dynamics on ultrafast timescales enables unique and new insights into important processes in the materials life sciences. In this respect, fundamental pump-probe approach based ultra-short photon pulses aims at creation of stroboscopic movies. Performing such experiments one many recently established accelerator-based 4th-generation light sources as free-electron lasers or superradiant THz allows an enormous widening accessible parameter space for excitation and/or probing...
Abstract Topologically protected surface states present rich physics and promising spintronic, optoelectronic, photonic applications that require a proper understanding of their ultrafast carrier dynamics. Here, we investigate these dynamics in topological insulators (TIs) the bismuth antimony chalcogenide family, where isolate response Dirac fermions at from bulk carriers by combining photoexcitation with below-bandgap terahertz (THz) photons TI samples varying Fermi level, including one...
Few-photon multiple ionization of ${\mathrm{N}}_{2}$ was studied differentially in a reaction microscope using 44 eV, $\ensuremath{\sim}25\text{ }\text{ }\mathrm{fs}$, intense ($\ensuremath{\sim}{10}^{13}\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$) photon pulses from FLASH. Sequential is observed to dominate. For various intermediate charge states $\mathrm{N}_{2}{}^{n+}$ we find considerable excess photons absorbed compared the minimum number that would energetically be required. Photoionization...
Narrow-band terahertz emission from coherently excited spin precession in metallic ferrimagnetic Mn3-xGa Heusler alloy nanofilms has been observed. The efficiency of the emission, per nanometer film thickness, is comparable or higher than that classical laser-driven sources based on optical rectification. center frequency films can be tuned precisely via composition range 0.20–0.35 THz, making this type a candidate for efficient on-chip emitters. Terahertz spectroscopy furthermore shown to...