327 research outputs found
Magnetic field dependence of antiferromagnetic resonance in NiO
We report on measurements of magnetic field and temperature dependence of antiferromagnetic resonances in the prototypical antiferromagnet NiO. The frequencies of the magnetic resonances in the vicinity of 1 THz have been determined in the time-domain via time-resolved Faraday measurements after selective excitation by narrow-band superradiant terahertz (THz) pulses at temperatures down to 3 K and in magnetic fields up to 10 T. The measurements reveal two antiferromagnetic resonance modes, which can be distinguished by their characteristic magnetic field dependencies. The nature of the two modes is discussed by comparison to an eight-sublattice antiferromagnetic model, which includes superexchange between the next-nearest-neighbor Ni spins, magnetic dipolar interactions, cubic magneto-crystalline anisotropy, and Zeeman interaction with the external magnetic field. Our study indicates that a two-sublattice model is insufficient for the description of spin dynamics in NiO, while the magnetic-dipolar interactions and magneto-crystalline anisotropy play important roles
Arrival time and intensity binning at unprecedented repetition rates
Understanding dynamics on ultrafast timescales enables unique and new insights
into important processes in the materials and life sciences. In this respect,
the fundamental pump-probe approach based on ultra-short photon pulses aims at
the creation of stroboscopic movies. Performing such experiments at one of the
many recently established accelerator-based 4th-generation light sources such
as free-electron lasers or superradiant THz sources allows an enormous
widening of the accessible parameter space for the excitation and/or probing
light pulses. Compared to table-top devices, critical issues of this type of
experiment are fluctuations of the timing between the accelerator and external
laser systems and intensity instabilities of the accelerator-based photon
sources. Existing solutions have so far been only demonstrated at low
repetition rates and/or achieved a limited dynamic range in comparison to
table-top experiments, while the 4th generation of accelerator-based light
sources is based on superconducting radio-frequency technology, which enables
operation at MHz or even GHz repetition rates. In this article, we present the
successful demonstration of ultra-fast accelerator-laser pump-probe
experiments performed at an unprecedentedly high repetition rate in the few-
hundred-kHz regime and with a currently achievable optimal time resolution of
13 fs (rms). Our scheme, based on the pulse-resolved detection of multiple
beam parameters relevant for the experiment, allows us to achieve an excellent
sensitivity in real-world ultra-fast experiments, as demonstrated for the
example of THz-field-driven coherent spin precession
Femtosecond laser spectroscopy for Exploration of Space
Space agencies around the world have the exploration of solar system bodies in the focus of their activities for decades already. The search for traces of life and to a better understanding of the geology of planets, moons and asteroids motivates these explorations. Our (DLR institute for Optical Sensor Systems (DLR-OS)) contribution to this topic is the development of spectroscopic sensors for material identification. DLR-OS is developing a wide range of spectroscopic sensors that reach from passive infrared spectrometers for remote sensing employed on orbiters to active laser spectroscopies such as NIR spectroscopy, Raman spectroscopy or Laser-Induced Breakdown Spectroscopy that are employed on robotic lander missions. Space, weight and power restrictions as well as robustness against harsh environmental conditions are inherent prerequisites for space missions and lead to specific design solutions for these instruments. Driven by emerging technology of space ready shortpulsed (femtosecond) lasers we are introducing the new topic of time domain spectroscopies to space exploration. In this work, we present our first results on coherent phonon and THz time domain spectroscopies on space relevant minerals.XVI Photonics Workshop : Book of abstracts; March 12-15, 2023; Kopaonik, Serbi
Ultrafast High-Field THz beamline at X-ray FEL
THz sources at FLASH utilize spent electron beam from a soft X-ray FEL to generate very intense (up to 150µJ), tunable frequency (1-300THz) and ultrafast narrowband (~10%) THz pulses, which are naturally synchronized to soft X-ray pulses [1]. This unique combination allows for wide range of element specific pump-probe experiments in physics, material science and biology. Here we discuss the unique features of the FLASH THz pulses and the accelerator source that bring along a set of challenges in the diagnostics of their key parameters: pulse energy, spectral, temporal and spatial profiles.VII International School and Conference on Photonics : PHOTONICA2019 : Abstracts of Tutorial, Keynote, Invited Lectures, Progress Reports and Contributed Papers; August 26-30; Belgrad
Volt-per-Ångstrom terahertz fields from X-ray free-electron lasers
The electron linear accelerators driving modern X-ray free-electron lasers can emit intense, tunable, quasi-monochromatic terahertz (THz) transients with peak electric fields of V Å ⁻¹ and peak magnetic fields in excess of 10 T when a purpose-built, compact, superconducting THz undulator is implemented. New research avenues such as X-ray movies of THz-driven mode-selective chemistry come into reach by making dual use of the ultra-short GeV electron bunches, possible by a rather minor extension of the infrastructure
Perturbative regime of terahertz high-harmonics generation in topological insulators
In this Letter, terahertz high harmonic generation processes in topological
insulators of the bismuth and antimony chalcogenides family are investigated.
Field conversion efficiencies are determined and clean cubic and quintic
power-law scaling is observed for third and fifth harmonics, up to driving
terahertz fields of 140 kV/cm. This is in contrast to all previous experiments
on terahertz harmonics generation in Dirac materials where a non-perturbative
regime has been observed already at few 10s kV/cm driving fields. Our nonlinear
THz spectroscopy experiments are complemented by THz pump - optical probe
measurements showing distinctly different relaxation dynamics of the carriers
in the topologically-protected Dirac states at the surfaces and the bulk. The
THz-induced dynamics of surface states reveal ultrafast relaxation that
prevents accumulation effects, and results in a clear perturbative regime of
THz harmonics generation that is different to graphene or Dirac semimetals with
their slower relaxation times in the few ps regime
Probing photo-induced melting of antiferromagnetic order in La0.5Sr1.5MnO4 by ultrafast resonant soft X-ray diffraction
Photo-excitation in complex oxides1 transfers charge across semicovalent
bonds, drastically perturbing spin and orbital orders2. Light may then be used
in compounds like magnetoresistive manganites to control magnetism on nanometre
lengthscales and ultrafast timescales. Here, we show how ultrafast resonant
soft x-ray diffraction can separately probe the photo-induced dynamics of spin
and orbital orders in La0.5Sr1.5MnO4. Ultrafast melting of CE antiferromagnetic
spin order is evidenced by the disappearance of a (1/4,1/4,1/2) diffraction
peak. On the other hand the (1/4,1/4,0) peak, reflecting orbital order, is only
partially reduced. Cluster calculations aid our interpretation by considering
different magnetically ordered states accessible after photo-excitation.
Nonthermal coupling between light and magnetism emerges as a primary aspect of
photo-induced phase transitions in manganites.Comment: 7 pages manuscript, 4 figure
Terahertz signatures of ultrafast Dirac fermion relaxation at the surface of topological insulators
Topologically protected surface states present rich physics and promising spintronic, optoelectronic, and photonic applications that require a proper understanding of their ultrafast carrier dynamics. Here, we investigate these dynamics in topological insulators (TIs) of the bismuth and antimony chalcogenide family, where we isolate the response of Dirac fermions at the surface from the response of bulk carriers by combining photoexcitation with below-bandgap terahertz (THz) photons and TI samples with varying Fermi level, including one sample with the Fermi level located within the bandgap. We identify distinctly faster relaxation of charge carriers in the topologically protected Dirac surface states (few hundred femtoseconds), compared to bulk carriers (few picoseconds). In agreement with such fast cooling dynamics, we observe THz harmonic generation without any saturation effects for increasing incident fields, unlike graphene which exhibits strong saturation. This opens up promising avenues for increased THz nonlinear conversion efficiencies, and high-bandwidth optoelectronic and spintronic information and communication applications.Parts of this research were carried out at ELBE at the Helmholtz-Zentrum Dresden-Rossendorf e.V., a member of the Helmholtz Association. The films are grown in IRE RAS within the framework of the state task. This work was supported by the RFBR grants Nos. 18-29-20101, 19-02-00598. N.A., S.K., and I.I. acknowledge support from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 737038 (TRANSPIRE). T.V.A.G.O. and L.M.E. acknowledge the support by the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter (ct.qmat). K.-J.T. acknowledges funding from the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 804349 (ERC StG CUHL) and financial support through the MAINZ Visiting Professorship. ICN2 was supported by the Severo Ochoa program from Spanish MINECO Grant No. SEV-2017-0706
Femtosecond laser spectroscopy for exploration of space
Space agencies around the world have the exploration of solar system bodies in the focus of their activities for decades already. The search for traces of life and to a better understanding of the geology of planets, moons and asteroids motivates these explorations. Our (DLR institute for Optical Sensor Systems (DLR-OS)) contribution to this topic is the development of spectroscopic sensors for material identification. DLR-OS is developing a wide range of spectroscopic sensors that reach from passive infrared spectrometers for remote sensing employed on orbiters to active laser spectroscopies such as NIR spectroscopy, Raman spectroscopy or Laser-Induced Breakdown Spectroscopy that are employed on robotic lander missions. Space, weight and power restrictions as well as robustness against harsh environmental conditions are inherent prerequisites for space missions and lead to specific design solutions for these instruments. Driven by emerging technology of space ready short-pulsed (femtosecond) lasers [1,2], we are introducing the new topic of time domain spectroscopies to space exploration. In this work, we present our first results on coherent phonon and THz time domain spectroscopies on space relevant minerals.IX International School and Conference on Photonics : PHOTONICA2023 : book of abstracts; August 28 - September 1, 2023; Belgrad
TESLA Technical Design Report Part III: Physics at an e+e- Linear Collider
The TESLA Technical Design Report Part III: Physics at an e+e- Linear
ColliderComment: 192 pages, 131 figures. Some figures have reduced quality. Full
quality figures can be obtained from http://tesla.desy.de/tdr. Editors -
R.-D. Heuer, D.J. Miller, F. Richard, P.M. Zerwa
- …