34 results on '"Timm Rohwer"'
Search Results
2. THz-Enhanced DC Ultrafast Electron Diffractometer
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Dongfang Zhang, Tobias Kroh, Felix Ritzkowsky, Timm Rohwer, Moein Fakhari, Huseyin Cankaya, Anne-Laure Calendron, Nicholas H. Matlis, and Franz X. Kärtner
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Physics ,QC1-999 ,Applied optics. Photonics ,TA1501-1820 - Abstract
Terahertz- (THz-) based electron manipulation has recently been shown to hold tremendous promise as a technology for manipulating and driving the next generation of compact ultrafast electron sources. Here, we demonstrate an ultrafast electron diffractometer with THz-driven pulse compression. The electron bunches from a conventional DC gun are compressed by a factor of 10 and reach a duration of ~180 fs (FWHM) with 10,000 electrons/pulse at a 1 kHz repetition rate. The resulting ultrafast electron source is used in a proof-of-principle experiment to probe the photoinduced dynamics of single-crystal silicon. The THz-compressed electron beams produce high-quality diffraction patterns and enable the observation of the ultrafast structural dynamics with improved time resolution. These results validate the maturity of THz-driven ultrafast electron sources for use in precision applications.
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- 2021
- Full Text
- View/download PDF
3. All-optical three-dimensional electron pulse compression
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Liang Jie Wong, Byron Freelon, Timm Rohwer, Nuh Gedik, and Steven G Johnson
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attosecond imaging ,ultrafast techniques ,ultrashort electron pulses ,bunch compression ,beam focusing ,optical traps ,Science ,Physics ,QC1-999 - Abstract
We propose an all-optical, three-dimensional electron pulse compression scheme in which Hermite–Gaussian optical modes are used to fashion a three-dimensional optical trap in the electron pulse’s rest frame. We show that the correct choices of optical incidence angles are necessary for optimal compression. We obtain analytical expressions for the net impulse imparted by Hermite–Gaussian free-space modes of arbitrary order. Although we focus on electrons, our theory applies to any charged particle and any particle with non-zero polarizability in the Rayleigh regime. We verify our theory numerically using exact solutions to Maxwell’s equations for first-order Hermite–Gaussian beams, demonstrating single-electron pulse compression factors of $\gt {{10}^{2}}$ in both longitudinal and transverse dimensions with experimentally realizable optical pulses. The proposed scheme is useful in ultrafast electron imaging for both single- and multi-electron pulse compression, and as a means of circumventing temporal distortions in magnetic lenses when focusing ultrashort electron pulses. Other applications include the creation of flat electron beams and ultrashort electron bunches for coherent terahertz emission.
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- 2015
- Full Text
- View/download PDF
4. Parameter sensitivities in tilted-pulse-front based terahertz setups and their implications for high-energy terahertz source design and optimization
- Author
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Tobias, Kroh, Timm, Rohwer, Dongfang, Zhang, Umit, Demirbas, Huseyin, Cankaya, Michael, Hemmer, Yi, Hua, Luis E, Zapata, Mikhail, Pergament, Franz X, Kärtner, and Nicholas H, Matlis
- Abstract
Despite the popularity and ubiquity of the tilted-pulse-front technique for single-cycle terahertz (THz) pulse generation, there is a deficit of experimental studies comprehensively mapping out the dependence of the performance on key setup parameters. The most critical parameters include the pulse-front tilt, the effective length of the pump pulse propagation within the crystal as well as effective length over which the THz beam interacts with the pump before it spatially walks off. Therefore, we investigate the impact of these parameters on the conversion efficiency and the shape of the THz beam via systematically scanning the 5D parameter space spanned by pump fluence, pulse-front-tilt, crystal-position (2D), and the pump size experimentally. We verify predictions so far only made by theory regarding the optimum interaction lengths and map out the impact of cascading on the THz radiation generation process. Furthermore, distortions imposed on the spatial THz beam profile for larger than optimum interaction lengths are observed. Finally, we identify the most sensitive parameters and, based on our findings, propose a robust optimization strategy for tilted-pulse-front THz setups. These findings are relevant for all THz strong-field applications in high demand of robust high-energy table-top single-cycle THz sources such as THz plasmonics, high-harmonic generation in solids as well as novel particle accelerators and beam manipulators.
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- 2022
5. Interaction Lengths in Tilted-pulse-front Terahertz Setups
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Tobias Kroh, Timm Rohwer, Umit Demirbas, Huseyin Çankaya, Michael Hemmer, Yi Hua, Mikhail Pergament, Nicholas H. Matlis, and Franz X. Kärtner
- Abstract
We map out the impact of the interaction lengths on the efficiency and terahertz spatial profile in tilted-pulse-front setups via systematically scanning the 5D-parameter space spanned by fluence, pulse-front tilt, crystal-position, and beam size.
- Published
- 2022
6. Ultrafast electron diffraction powered with a Terahertz-driven pulse compressor
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Moein Fakhari, Felix Ritzkowsky, Tobias Kroh, Franz X. Kärtner, Nicholas H. Matlis, Timm Rohwer, Anne-Laure Calendron, Dongfang Zhang, and Huseyin Cankaya
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Diffraction ,Brightness ,Materials science ,business.industry ,Terahertz radiation ,Ultrafast electron diffraction ,Femtosecond ,Physics::Optics ,Optoelectronics ,Electron ,Radiation ,business ,Ultrashort pulse - Abstract
Ultrafast electron sources have emerged as a powerful tool for revealing structural dynamics in molecules and materials at the atomic scale [1] . Over the past years, there has been great interest in achieving sub-100 femtosecond (fs) time resolution with sufficient brightness, and high repetition rate to enable a direct observation of primary events governing physical/chemical processes [1] . Recently, it has been shown that laser-based Terahertz (THz) radiation powered electron acceleration and manipulation provides a promising solution to construct future ultrafast electron sources that support high energy, high repetition rate, short electron bunches while being compact [2] – [3] .
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- 2021
7. Time-resolved XUV ARPES with tunable 24–33 eV laser pulses at 30 meV resolution
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Nuh Gedik, Edbert J. Sie, Timm Rohwer, and Changmin Lee
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0301 basic medicine ,Photoemission spectroscopy ,Science ,General Physics and Astronomy ,Angle-resolved photoemission spectroscopy ,02 engineering and technology ,Photon energy ,Characterization and analytical techniques ,General Biochemistry, Genetics and Molecular Biology ,Article ,law.invention ,Superconducting properties and materials ,03 medical and health sciences ,Optics ,law ,Condensed Matter::Superconductivity ,High harmonic generation ,lcsh:Science ,Solid-state lasers ,Monochromator ,Physics ,Multidisciplinary ,business.industry ,General Chemistry ,021001 nanoscience & nanotechnology ,Laser ,030104 developmental biology ,Femtosecond ,Condensed Matter::Strongly Correlated Electrons ,lcsh:Q ,0210 nano-technology ,business ,Ultrashort pulse - Abstract
High harmonic generation of ultrafast laser pulses can be used to perform angle-resolved photoemission spectroscopy (ARPES) to map the electronic band structure of materials with femtosecond time resolution. However, currently it is difficult to reach high momenta with narrow energy resolution. Here, we combine a gas phase extreme ultraviolet (XUV) femtosecond light source, an XUV monochromator, and a time-of-flight electron analyzer to develop XUV-based time-resolved ARPES. Our technique can produce tunable photon energy between 24–33 eV with an unprecedented energy resolution of 30 meV and time resolution of 200 fs. This technique enables time-, energy- and momentum-resolved investigation of the nonequilibrium dynamics of electrons in materials with a full access to their first Brillouin zone. We evaluate the performance of this setup through exemplary measurements on various quantum materials, including WTe2, WSe2, TiSe2, and Bi2Sr2CaCu2O8+δ., Currently, it is difficult to reach high momenta with narrow energy resolution via laser-based angle-resolved photoemission spectroscopy (ARPES). Here, Sie et al. develop a time-resolved XUV based ARPES setup which can access the first Brillouin zone of all materials with narrow energy resolution.
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- 2019
8. Evidence for topological defects in a photoinduced phase transition
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Anshul Kogar, Pablo Jarillo-Herrero, Ian R. Fisher, Ya-Qing Bie, A.V. Rozhkov, Philip Walmsley, Boris V. Fine, Nuh Gedik, Timm Rohwer, Edoardo Baldini, Emre Ergecen, Hengyun Zhou, Byron Freelon, Pavel E. Dolgirev, Joshua Straquadine, Edbert J. Sie, Changmin Lee, Alfred Zong, and Mehmet Yilmaz
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Thermal equilibrium ,Physics ,Phase transition ,General Physics and Astronomy ,01 natural sciences ,010305 fluids & plasmas ,Topological defect ,Amplitude ,Chemical physics ,Picosecond ,0103 physical sciences ,010306 general physics ,Ground state ,Ultrashort pulse ,Charge density wave - Abstract
Upon excitation with an intense laser pulse, a symmetry-broken ground state can undergo a non-equilibrium phase transition through pathways different from those in thermal equilibrium. The mechanism underlying these photoinduced phase transitions has long been researched in the study of condensed matter systems1, but many details in this ultrafast, non-adiabatic regime still remain to be clarified. To this end, we investigate the light-induced melting of a unidirectional charge density wave (CDW) in LaTe3. Using a suite of time-resolved probes, we independently track the amplitude and phase dynamics of the CDW. We find that a fast (approximately 1 picosecond) recovery of the CDW amplitude is followed by a slower re-establishment of phase coherence. This longer timescale is dictated by the presence of topological defects: long-range order is inhibited and is only restored when the defects annihilate. Our results provide a framework for understanding other photoinduced phase transitions by identifying the generation of defects as a governing mechanism. Three different ultrafast probes investigate a non-adiabatic phase transition and find substantial evidence of topological defects inhibiting the reformation of the equilibrium phase.
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- 2018
9. Ultrafast electron diffractometer with Terahertz-driven pulse compression
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Nicholas H. Matlis, Franz X. Kärtner, Dongfang Zhang, Moein Fakhari, Timm Rohwer, Tobias Kroh, Felix Ritzkowsky, Anne-Laure Calendron, and Huseyin Cankaya
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Diffraction ,Materials science ,Silicon ,business.industry ,Terahertz radiation ,FOS: Physical sciences ,Physics::Optics ,chemistry.chemical_element ,Pulse (physics) ,chemistry ,Pulse compression ,Temporal resolution ,Physics::Atomic and Molecular Clusters ,Optoelectronics ,Physics::Chemical Physics ,business ,Ultrashort pulse ,Optics (physics.optics) ,Physics - Optics ,Diffractometer - Abstract
Terahertz (THz)-based electron manipulation has recently been shown to hold tremendous promise as a technology for manipulating and driving the next-generation of compact ultrafast electron sources. Here, we demonstrate an ultrafast electron diffractometer with THz-driven pulse compression. The electron bunches from a conventional DC gun are compressed by a factor of 10 and reach a duration of ~180 fs (FWHM) with 10,000 electrons/pulse at a 1 kHz repetition rate. The resulting ultrafast electron source is used in a proof-of-principle experiment to probe the photoinduced dynamics of single-crystal silicon. The THz-compressed electron beams produce high-quality diffraction patterns and enable observation of the ultrafast structural dynamics with improved time resolution. These results validate the maturity of THz-driven ultrafast electron sources for use in precision applications., 16 pages, 5 figures. arXiv admin note: text overlap with arXiv:1910.06639
- Published
- 2021
10. Compact THz Photogun Transversely Pumped By Twin Single-Cycle Pulses
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Umit Demirbas, Mikhail Pergament, Hannes Dinter, Timm Rohwer, Max Kellermeier, Ralph Aßmann, Michael Hemmer, Moein Fakhari, Tobias Kroh, Huseyin Cankaya, Franz X. Kärtner, and Nicholas H. Matlis
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Diffraction ,Photoexcitation ,Materials science ,Spectrometer ,business.industry ,Terahertz radiation ,Optoelectronics ,Electric potential ,Electron ,business ,Single cycle - Abstract
A compact terahertz (THz) powered photogun reaching electron energies up to ~ 3keV is presented. First experiments testing the performance of the device as well as challenges in future development are summarized and discussed.
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- 2021
11. THz-Enhanced DC Ultrafast Electron Diffractometer
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Anne-Laure Calendron, Moein Fakhari, Felix Ritzkowsky, Dongfang Zhang, Nicholas H. Matlis, Tobias Kroh, Timm Rohwer, Franz X. Kärtner, and Huseyin Cankaya
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Diffraction ,Materials science ,Silicon ,Terahertz radiation ,business.industry ,Physics ,QC1-999 ,chemistry.chemical_element ,Physics::Optics ,Electron ,TA1501-1820 ,Full width at half maximum ,chemistry ,Pulse compression ,Optoelectronics ,Applied optics. Photonics ,ddc:500 ,business ,Ultrashort pulse ,Diffractometer - Abstract
Ultrafast science 2021, 9848526 (2021). doi:10.34133/2021/9848526, Terahertz- (THz-) based electron manipulation has recently been shown to hold tremendous promise as a technology formanipulating and driving the next generation of compact ultrafast electron sources. Here, we demonstrate an ultrafast electrondiffractometer with THz-driven pulse compression. The electron bunches from a conventional DC gun are compressed by afactor of 10 and reach a duration of ~180 fs (FWHM) with 10,000 electrons/pulse at a 1 kHz repetition rate. The resultingultrafast electron source is used in a proof-of-principle experiment to probe the photoinduced dynamics of single-crystal silicon.The THz-compressed electron beams produce high-quality diffraction patterns and enable the observation of the ultrafaststructural dynamics with improved, Published by American Association for the Advancement of Science, AAAS, Washington, DC
- Published
- 2021
12. Powering a Photogun using Single-Cycle Terahertz
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Max Kellermeier, Michael Hemmer, Tobias Kroh, R. Abmann, Franz X. Kärtner, Moein Fakhari, Mikhail Pergament, Hannes Dinter, Umit Demirbas, Timm Rohwer, Huseyin Cankaya, and Nicholas H. Matlis
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Coupling ,Physics ,Front and back ends ,business.industry ,Terahertz radiation ,Couplings ,Linear accelerators ,Optoelectronics ,business ,Energy (signal processing) ,Linear particle accelerator ,Single cycle - Abstract
Development of THz-powered photoguns promises to bring benefits to many applications by scaling down the size and cost of these devices as well as creating new capabilities. In particular, THz photoguns producing MeV beams are desired as the front end for THz-powered LINACs. Generating sufficient THz energy, however, is challenging, as is transporting and coupling the THz into the gun. We present initial results on development of the THz source and transport for an MeV gun.
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- 2020
13. THz photogun transversely pumped by twin single-cycle pulses
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Umit Demirbas, Franz X. Kärtner, R. Abmann, Michael Hemmer, Mikhail Pergament, Nicholas H. Matlis, Timm Rohwer, Tobias Kroh, Hannes Dinter, Huseyin Cankaya, Moein Fakhari, and Max Kellermeier
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Physics ,Field (physics) ,010308 nuclear & particles physics ,business.industry ,Terahertz radiation ,Electric breakdown ,01 natural sciences ,Wavelength ,Optics ,0103 physical sciences ,High field ,010306 general physics ,business ,Scaling ,Single cycle - Abstract
Scaling the RF-photogun concept to terahertz (THz) frequencies brings several compelling advantages, including compactness, intrinsic timing between the photoemission and driving field sources, and high field gradients associated with the short THz wavelength and high breakdown threshold. These benefits, however, come at the cost of smaller dimensions and tighter tolerances which are challenging to reach in practice. Here we summarize first experiments testing the performance of a THz photogun pumped transversely by twin single-cycle THz pulses and discuss challenges facing future development of the concept.
- Published
- 2020
14. Robust optimization of single-cycle THz setups based on phase-matching via tilted pulse fronts using an incident-fluence metric
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Mikhail Pergament, Timm Rohwer, Tobias Kroh, Nicholas H. Matlis, Umit Demirbas, Lu Wang, Franz X. Kärtner, Huseyin Cankaya, Schunemann, Peter G., and Schepler, Kenneth L.
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Physics ,business.industry ,Terahertz radiation ,Physics::Optics ,Robust optimization ,Fluence ,Pulse (physics) ,Optics ,Metric (mathematics) ,ddc:620 ,business ,Phase matching ,Single cycle - Abstract
Nonlinear Frequency Generation and Conversion: Materials and Devices XIX, San Francisco, United States, 1 Feb 2020 - 6 Feb 2020; Proceedings of SPIE 11264, 1126416 (2020). doi:10.1117/12.2545145, Despite the popularity and ubiquitousness of the tilted-pulse-front technique for single-cycle terahertz (THz) generation, optimization of the experimental setup remains complex and difficult due to the sensitive dependence on and coupling between the optical pulse parameters, including fluence, beam size, angular dispersion and temporal compression. Here we present a systematic and robust method to tune the tilted pulse-front setup, based on use of selected multi-dimensional scans, which enables a straight-forward and accurate determination of optimum parameter values. Our methodology not only allows us to determine parameter sensitivities and achieve a robust optimum in the performance, but also enables a verification of certain physical properties of the lithium niobate prism, including the THz refractive index. The detailed step-by-step procedure is discussed and applied to a tilted-pulse-front THz setup at both room temperature and cryogenic temperatures. The procedure can be applied to any setup based on the tilted-pulse-front geometry and is important for the construction of high energy THz sources required for strong field terahertz applications such as novel particle acceleration schemes or beam manipulators., Published by SPIE, Bellingham, Wash.
- Published
- 2020
15. Light-induced charge density wave in LaTe3
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Xiaozhe Shen, Nuh Gedik, Stephen Weathersby, Haidan Wen, Timm Rohwer, Xijie Wang, Alfred Zong, Edbert J. Sie, Renkai Li, Pavel E. Dolgirev, Yafang Yang, Ian R. Fisher, Joshua Straquadine, Ya-Qing Bie, Xirui Wang, Pablo Jarillo-Herrero, Michael Kozina, Jie Yang, I-Cheng Tung, Suji Park, and Anshul Kogar
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Fluids & Plasmas ,General Physics and Astronomy ,FOS: Physical sciences ,Electron ,01 natural sciences ,Mathematical Sciences ,010305 fluids & plasmas ,Density wave theory ,Condensed Matter - Strongly Correlated Electrons ,Phase (matter) ,0103 physical sciences ,010306 general physics ,Physics ,Thermal equilibrium ,Condensed Matter - Materials Science ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Ultrafast electron diffraction ,Neurosciences ,Materials Science (cond-mat.mtrl-sci) ,cond-mat.mtrl-sci ,Excited state ,Physical Sciences ,State of matter ,Condensed Matter::Strongly Correlated Electrons ,cond-mat.str-el ,Charge density wave - Abstract
When electrons in a solid are excited by light, they can alter the free energy landscape and access phases of matter that are out of reach in thermal equilibrium. This accessibility becomes important in the presence of phase competition, when one state of matter is preferred over another by only a small energy scale that, in principle, is surmountable by the excitation. Here, we study a layered compound, LaTe3, where a small lattice anisotropy in the a–c plane results in a unidirectional charge density wave (CDW) along the c axis1,2. Using ultrafast electron diffraction, we find that, after photoexcitation, the CDW along the c axis is weakened and a different competing CDW along the a axis subsequently emerges. The timescales characterizing the relaxation of this new CDW and the reestablishment of the original CDW are nearly identical, which points towards a strong competition between the two orders. The new density wave represents a transient non-equilibrium phase of matter with no equilibrium counterpart, and this study thus provides a framework for discovering similar states of matter that are ‘trapped’ under equilibrium conditions. Short pulses of light shift the balance between two competing charge density wave phases, allowing the weaker one to manifest transiently while suppressing the stronger one. This shows that competing phases can be tuned in a non-equilibrium setting.
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- 2020
16. Dynamical Slowing-Down in an Ultrafast Photoinduced Phase Transition
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Joshua Straquadine, Xijie Wang, Xiaozhe Shen, Ian R. Fisher, Benjamin K. Ofori-Okai, I-Cheng Tung, Timm Rohwer, Pavel E. Dolgirev, Suji Park, Pablo Jarillo-Herrero, Ya-Qing Bie, Jie Yang, Yafang Yang, Nuh Gedik, Anshul Kogar, Haidan Wen, Michael Kozina, Emre Ergecen, Renkai Li, Matthias C. Hoffmann, Mehmet Yilmaz, Xirui Wang, and Alfred Zong
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Physics ,Condensed Matter - Materials Science ,Phase transition ,Phase boundary ,General Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Slowdown ,Complex system ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,General Physics and Astronomy ,Non-equilibrium thermodynamics ,01 natural sciences ,Landau theory ,cond-mat.mtrl-sci ,Mathematical Sciences ,Photoexcitation ,Condensed Matter - Strongly Correlated Electrons ,Engineering ,0103 physical sciences ,Femtosecond ,Physical Sciences ,cond-mat.str-el ,010306 general physics - Abstract
Complex systems, which consist of a large number of interacting constituents, often exhibit universal behavior near a phase transition. A slowdown of certain dynamical observables is one such recurring feature found in a vast array of contexts. This phenomenon, known as critical slowing down, is well studied mostly in thermodynamic phase transitions. However, it is less understood in highly nonequilibrium settings, where the time it takes to traverse the phase boundary becomes comparable to the timescale of dynamical fluctuations. Using transient optical spectroscopy and femtosecond electron diffraction, we studied a photo-induced transition of a model charge-density-wave (CDW) compound, LaTe$_3$. We observed that it takes the longest time to suppress the order parameter at the threshold photoexcitation density, where the CDW transiently vanishes. This finding can be quantitatively captured by generalizing the time-dependent Landau theory to a system far from equilibrium. The experimental observation and theoretical understanding of dynamical slowing down may offer insight into other general principles behind nonequilibrium phase transitions in many-body systems.
- Published
- 2019
17. Combining time-resolved optical (TOS), electronic (trARPES) and structural (UED) probes on the class of rare earth tritellurides RTe3
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Hengyun Zhou, Alfred Zong, Edbert J. Sie, Ian R. Fisher, Byron Freelon, Pavel E. Dolgirev, Emre Ergecen, Anshul Kogar, Pablo Jarillo-Herrero, Mehmet Yilmaz, Philip Walmsley, Timm Rohwer, A.V. Rozhkov, Joshua Straquadine, Nuh Gedik, Boris V. Fine, Changmin Lee, Edoardo Baldini, and Ya-Qing Bie
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Physics ,Class (set theory) ,QC1-999 ,Rare earth ,Physics::Optics ,Astrophysics - Abstract
The combination of EUV based time-resolved Angle-Resolved-Photo-Electron-Spectroscopy (trARPES), Ultrafast-Electron-Diffraction (UED) and Transient-Optical-Spectroscopy (TOS) facilitates a comprehensive study and all-embracing analysis of correlated dynamics, exemplified on the system of Charge-Density-Waves (CDW’s) in rare earth tritellurides (RTe3).
- Published
- 2019
18. Ultrafast manipulation of mirror domain walls in a charge density wave
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Jie Yang, Joseph Checkelsky, Xijie Wang, Alfred Zong, Debanjan Chowdhury, Xiaozhe Shen, Nuh Gedik, Linda Ye, Byron Freelon, Anshul Kogar, Carolyn Marks, Timm Rohwer, Stephen Weathersby, and Renkai Li
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Materials science ,Phonon ,Physics::Optics ,FOS: Physical sciences ,02 engineering and technology ,Electron ,01 natural sciences ,Charge ordering ,0103 physical sciences ,Physics::Atomic and Molecular Clusters ,010306 general physics ,Computer Science::Operating Systems ,Computer Science::Databases ,Research Articles ,Superconductivity ,Condensed Matter - Materials Science ,Multidisciplinary ,Condensed matter physics ,Physics ,SciAdv r-articles ,Materials Science (cond-mat.mtrl-sci) ,021001 nanoscience & nanotechnology ,cond-mat.mtrl-sci ,Electron diffraction ,Femtosecond ,0210 nano-technology ,Ultrashort pulse ,Charge density wave ,Research Article - Abstract
Topological defects, potential information carriers, were written into and erased from a solid with femtosecond light pulses., Domain walls (DWs) are singularities in an ordered medium that often host exotic phenomena such as charge ordering, insulator-metal transition, or superconductivity. The ability to locally write and erase DWs is highly desirable, as it allows one to design material functionality by patterning DWs in specific configurations. We demonstrate such capability at room temperature in a charge density wave (CDW), a macroscopic condensate of electrons and phonons, in ultrathin 1T-TaS2. A single femtosecond light pulse is shown to locally inject or remove mirror DWs in the CDW condensate, with probabilities tunable by pulse energy and temperature. Using time-resolved electron diffraction, we are able to simultaneously track anti-synchronized CDW amplitude oscillations from both the lattice and the condensate, where photoinjected DWs lead to a red-shifted frequency. Our demonstration of reversible DW manipulation may pave new ways for engineering correlated material systems with light.
- Published
- 2018
19. Does the excitation wavelength affect the ultrafast quenching dynamics of the charge-density wave in 1 T -TiSe 2 ?
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Lutz Kipp, Timm Rohwer, G. Rohde, C. Sohrt, Lexian Yang, Kai Rossnagel, K. Hanff, Michael Bauer, and A. Stange
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Radiation ,Quenching (fluorescence) ,Chemistry ,Charge density ,Condensed Matter Physics ,Electromagnetic radiation ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Wavelength ,Secondary emission ,Physical and Theoretical Chemistry ,Atomic physics ,Fermi gas ,Charge density wave ,Spectroscopy ,Excitation - Abstract
The ultrafast spectral responses of a charge-ordered state in 1 T -TiSe 2 to the photo-excitation with laser-pulses of 790 nm and 395 nm center wavelength are compared. Time- and angle-resolved photoemission reveals pronounced differences in the energy-momentum distribution of the nascent electron gas; a distinct effect of the distribution character on the destruction dynamics of the charge-ordered state is, however, not observed.
- Published
- 2014
20. Self-amplified photo-induced gap quenching in a correlated electron material
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Henry C. Kapteyn, Martin Aeschlimann, Piotr Matyba, A. Ruffing, Adra Carr, A. Stange, Michael Bauer, Lutz Kipp, M. Wiesenmayer, Margaret M. Murnane, Stephan Michael, Kai Rossnagel, J. Urbancic, S. Jakobs, S. Hellmann, Hans Christian Schneider, Stefan Mathias, Tenio Popmintchev, Steffen Eich, Sebastian Emmerich, Timm Rohwer, Cong Chen, Massachusetts Institute of Technology. Department of Physics, Francis Bitter Magnet Laboratory (Massachusetts Institute of Technology), and Rohwer, Timm
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Physics ,Multidisciplinary ,Band gap ,Science ,General Physics and Astronomy ,02 engineering and technology ,General Chemistry ,Electron ,021001 nanoscience & nanotechnology ,01 natural sciences ,Article ,General Biochemistry, Genetics and Molecular Biology ,Multiple exciton generation ,Impact ionization ,Excited state ,0103 physical sciences ,gap quenching ,electron material ,Atomic physics ,010306 general physics ,0210 nano-technology ,Electronic band structure ,Characteristic energy ,Excitation - Abstract
Capturing the dynamic electronic band structure of a correlated material presents a powerful capability for uncovering the complex couplings between the electronic and structural degrees of freedom. When combined with ultrafast laser excitation, new phases of matter can result, since far-from-equilibrium excited states are instantaneously populated. Here, we elucidate a general relation between ultrafast non-equilibrium electron dynamics and the size of the characteristic energy gap in a correlated electron material. We show that carrier multiplication via impact ionization can be one of the most important processes in a gapped material, and that the speed of carrier multiplication critically depends on the size of the energy gap. In the case of the charge-density wave material 1T-TiSe2, our data indicate that carrier multiplication and gap dynamics mutually amplify each other, which explains—on a microscopic level—the extremely fast response of this material to ultrafast optical excitation., The non-equilibrium dynamics of correlated electron materials are still poorly understood. Here, the authors use time- and angle-resolved photoemission spectroscopy to show that carrier multiplication is important in initial non-equilibrium dynamics of 1T-TiSe2 and depends on the size of the energy gap.
- Published
- 2016
21. Tracking the relaxation pathway of photo-excited electrons in 1T-TiSe2
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G. Rohde, Timm Rohwer, Lutz Kipp, K. Hanff, S. Hellmann, Kai Rossnagel, A. Stange, C. Sohrt, Michael Bauer, Adra Carr, Henry C. Kapteyn, Lexian Yang, and Margaret M. Murnane
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Materials science ,Photoemission spectroscopy ,Excited state ,Femtosecond ,General Physics and Astronomy ,Relaxation (physics) ,General Materials Science ,Position and momentum space ,Physical and Theoretical Chemistry ,Atomic physics ,Absorption (electromagnetic radiation) ,Ultrashort pulse ,Excitation - Abstract
The ultrafast dynamics of excited electrons in 1T-TiSe2 after absorption of a 390 nm light pulse is probed by time- and angle-resolved photoemission spectroscopy using femtosecond XUV pulses. It is demonstrated that the experimental approach can provide a comprehensive view of hot carrier motion in momentum space during relaxation back to equilibrium. This capability opens a new avenue in the investigation of energy dissipation processes in solids after intense optical excitation.
- Published
- 2013
22. Two-photon photoemission from ex-situ prepared butanethiol SAMs on Au (111)
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Nils Heinemann, Jan Grunau, Timm Rohwer, O. Andreyev, T. Leissner, and Michael Bauer
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Crystallography ,chemistry.chemical_compound ,Chemistry ,Phase (matter) ,Monolayer ,General Physics and Astronomy ,Self-assembled monolayer ,Physical and Theoretical Chemistry ,Spectroscopy ,Butanethiol ,Resonance (particle physics) ,Deposition (law) ,Spectral line - Abstract
Self-assembled monolayers (SAMs) of butanethiol on a Au (111) single crystalline surface in the p x root 3 lying-down phase prepared by deposition from solution were studied with two-photon photoemission (2PPE) spectroscopy. The spectra reveal clear signatures of two unoccupied resonance states at energies E - E(F) = 3.7 eV and 3.9 eV. The low-energy state is assigned to the characteristic sigma*-resonance associated with the Au-S bond of the thiolate. The energy of the other resonance state agrees well with an interface state reported before for different alkanethiol SAMs on Au (111) in a standing-up phase. Furthermore the 2PPE data provide indications that the high quality of the ex-situ prepared SAMs support the formation of image potential states. (C) 2011 Elsevier B. V. All rights reserved.
- Published
- 2011
23. Time- and angle-resolved photoemission spectroscopy with optimized high-harmonic pulses using frequency-doubled Ti:Sapphire lasers
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Margaret M. Murnane, M. Wiesenmayer, Tenio Popmintchev, A. Ruffing, A. Stange, J. Urbancic, Henry C. Kapteyn, Martin Aeschlimann, Cong Chen, Adra Carr, Timm Rohwer, Klaus Jansen, Steffen Eich, S. Hellmann, Piotr Matyba, Lutz Kipp, S. Jakobs, Michael Bauer, Kai Rossnagel, and Stefan Mathias
- Subjects
Materials science ,Photoemission spectroscopy ,Inverse photoemission spectroscopy ,Time-resolved photoemission spectroscopy ,Physics::Optics ,Angle-resolved photoemission spectroscopy ,Atomic ,Physical Chemistry ,law.invention ,Optics ,Particle and Plasma Physics ,law ,Nuclear ,Physical and Theoretical Chemistry ,Spectroscopy ,Time-resolved ARPES ,Radiation ,Chemical Physics ,business.industry ,Molecular ,Laser ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Extreme-ultraviolet photoemission spectroscopy ,Femtosecond ,Harmonic ,Femtosecond dynamics ,Time-resolved spectroscopy ,business ,Two-photon photoemission ,Ultrashort pulse ,Physical Chemistry (incl. Structural) - Abstract
Time- and angle-resolved photoemission spectroscopy (trARPES) using femtosecond extreme ultraviolet high harmonics has recently emerged as a powerful tool for investigating ultrafast quasiparticle dynamics in correlated-electron materials. However, the full potential of this approach has not yet been achieved because, to date, high harmonics generated by 800 nm wavelength Ti:Sapphire lasers required a trade-off between photon flux, energy and time resolution. Photoemission spectroscopy requires a quasi-monochromatic output, but dispersive optical elements that select a single harmonic can significantly reduce the photon flux and time resolution. Here we show that 400 nm driven high harmonic extreme-ultraviolet trARPES is superior to using 800 nm laser drivers since it eliminates the need for any spectral selection, thereby increasing photon flux and energy resolution to
- Published
- 2014
24. Ultrafast Modulation of the Chemical Potential inBaFe2As2by Coherent Phonons
- Author
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Ilya Eremin, C. Sohrt, Timm Rohwer, Laurenz Rettig, F. Chen, Margaret M. Murnane, Uwe Bovensiepen, Kai Rossnagel, K. Hanff, A. Stange, Tenio Popmintchev, Donglai Feng, R. Cortés, T. Wolf, J. Fink, Michael Bauer, Lexian Yang, Henry C. Kapteyn, G. Rohde, Lutz Kipp, and B. Kamble
- Subjects
Physics ,Condensed matter physics ,Phonon ,Photoemission spectroscopy ,Fermi level ,General Physics and Astronomy ,Electron ,Electronic structure ,Coupling (probability) ,symbols.namesake ,symbols ,Sensitivity (control systems) ,Atomic physics ,Electronic band structure - Abstract
Time- and angle-resolved extreme ultraviolet photoemission spectroscopy is used to study the electronic structure dynamics in ${\mathrm{BaFe}}_{2}{\mathrm{As}}_{2}$ around the high-symmetry points $\mathrm{\ensuremath{\Gamma}}$ and $M$. A global oscillation of the Fermi level at the frequency of the ${A}_{1g}(\mathrm{As})$ phonon mode is observed. It is argued that this behavior reflects a modulation of the effective chemical potential in the photoexcited surface region that arises from the high sensitivity of the band structure near the Fermi level to the ${A}_{1g}(\mathrm{As})$ phonon mode combined with a low electron diffusivity perpendicular to the layers. The results establish a novel way to tune the electronic properties of iron pnictides: coherent control of the effective chemical potential. The results further suggest that the equilibration time for the effective chemical potential needs to be considered in the ultrafast electronic structure dynamics of materials with weak interlayer coupling.
- Published
- 2014
25. Time-domain classification of charge-density-wave insulators
- Author
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M. Kalläne, Henry C. Kapteyn, A. Stange, Kai Rossnagel, Michael Bauer, Timm Rohwer, Adra Carr, S. Hellmann, K. Hanff, C. Sohrt, Margaret M. Murnane, and Lutz Kipp
- Subjects
Condensed Matter::Quantum Gases ,Physics ,Multidisciplinary ,Condensed matter physics ,Photoemission spectroscopy ,General Physics and Astronomy ,Insulator (electricity) ,General Chemistry ,General Biochemistry, Genetics and Molecular Biology ,Condensed Matter::Strongly Correlated Electrons ,Time domain ,Charge density wave ,Temporal discrimination ,Ultrashort pulse - Abstract
Distinguishing insulators by the dominant type of interaction is a central problem in condensed matter physics. Basic models include the Bloch-Wilson and the Peierls insulator due to electron-lattice interactions, the Mott and the excitonic insulator caused by electron-electron interactions, and the Anderson insulator arising from electron-impurity interactions. In real materials, however, all the interactions are simultaneously present so that classification is often not straightforward. Here, we show that time- and angle-resolved photoemission spectroscopy can directly measure the melting times of electronic order parameters and thus identify-via systematic temporal discrimination of elementary electronic and structural processes-the dominant interaction. Specifically, we resolve the debates about the nature of two peculiar charge-density-wave states in the family of transition-metal dichalcogenides, and show that Rb intercalated 1T-TaS(2) is a Peierls insulator and that the ultrafast response of 1T-TiSe(2) is highly suggestive of an excitonic insulator.
- Published
- 2012
26. Probing the switching state of a surface-mounted azobenzene derivative using femtosecond XUV photoemission
- Author
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Jan Grunau, Rainer Herges, Sonja Kuhn, Nils Heinemann, Timm Rohwer, Dordaneh Zargarani, Olaf M. Magnussen, Lutz Kipp, Michael Bauer, and Ullrich Jung
- Subjects
Molecular switch ,Materials science ,Photoemission spectroscopy ,business.industry ,Inverse photoemission spectroscopy ,Angle-resolved photoemission spectroscopy ,chemistry.chemical_compound ,Optics ,Azobenzene ,chemistry ,Femtosecond ,High harmonic generation ,Atomic physics ,business ,Isomerization - Abstract
Photoemission spectroscopy using femtosecond XUV light pulses is applied to probe the isomerization state of the molecular switch 3-(4-(4-hexyl-phenylazo)-phenoxy)-propane-1-thiol deposited by liquid phase self-assembly on Au(111). Spectral shifts of valence-electronic signatures that we associate with the carbon C2s orbital enable us to distinguish the trans and the cis isomerization state of the adsorbed molecules. These preliminary results envision the potential to probe reversible switching processes of surface-mounted molecules in real time by tracking the temporal evolution of the electronic and nuclear degrees of freedom in a femtosecond XUV photoemission experiment.
- Published
- 2012
27. Time-Resolved X-Ray Photoelectron Spectroscopy at FLASH
- Author
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Alexander Föhlisch, F. Sorgenfrei, M. Marczynski-Bühlow, Harald Redlin, Michael Bauer, Wilfried Wurth, C. Sohrt, Martin Beye, Kai Rossnagel, Timm Rohwer, Franz Hennies, S. Hellmann, M. Kalläne, and Lutz Kipp
- Subjects
Physics ,General Physics and Astronomy ,Physics::Optics ,Nanosecond ,Laser ,Space charge ,Electron spectroscopy ,law.invention ,Optical pumping ,X-ray photoelectron spectroscopy ,law ,ddc:540 ,Atomic physics ,Spectroscopy ,Excitation - Abstract
The technique of time-resolved pump-probe x-ray photoelectron spectroscopy using the free-electron laser in Hamburg (FLASH) is described in detail. Particular foci lie on the macrobunch resolving detection scheme, the role of vacuum space-charge effects and the synchronization of pump and probe lasers. In an exemplary case study, the complete Ta 4f core-level dynamics in the layered charge-density-wave (CDW) compound 1T-TaS2 in response to impulsive optical excitation is measured on the sub-picosecond to nanosecond timescale. The observed multi-component dynamics is related to the intrinsic melting and reformation of the CDW as well as to extrinsic pump-laser-induced vacuum space-charge effects.
- Published
- 2012
28. Ultrafast Melting of a Charge-Density Wave in the Mott Insulator1T−TaS2
- Author
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Timm Rohwer, Lutz Kipp, Harald Redlin, Alexander Föhlisch, S. Hellmann, F. Sorgenfrei, M. Kalläne, M. Marczynski-Bühlow, Kai Rossnagel, Wilfried Wurth, Franz Hennies, Michael Bauer, C. Sohrt, and Martin Beye
- Subjects
Photoexcitation ,Phase transition ,Materials science ,Condensed matter physics ,Photoemission spectroscopy ,Mott insulator ,Femtosecond ,General Physics and Astronomy ,Atomic physics ,Metal–insulator transition ,Charge density wave ,Mott transition - Abstract
Femtosecond time-resolved core-level photoemission spectroscopy with a free-electron laser is used to measure the atomic-site specific charge-order dynamics of the charge-density wave in the Mott insulator 1T-TaS2. After strong photoexcitation, a prompt loss of charge order and subsequent fast equilibration dynamics of the electron-lattice system are observed. On the time scale of electron-phonon thermalization, about 1 ps, the system is driven across a phase transition from a long-range charge ordered state to a quasiequilibrium state with domainlike short-range charge and lattice order. The experiment opens the way to study the nonequilibrium dynamics of condensed matter systems with full elemental, chemical, and atomic-site selectivity.
- Published
- 2010
29. Collapse of long-range charge order tracked by time-resolved photoemission at high momenta
- Author
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M. Kalläne, S. Hellmann, A. Stange, Bartosz Slomski, Yanwei Liu, Lutz Kipp, Timm Rohwer, Kai Rossnagel, C. Sohrt, Luis Miaja Avila, Adra Carr, Stefan Mathias, Michael Bauer, and M. Wiesenmayer
- Subjects
Multidisciplinary ,Photon ,Condensed matter physics ,Chemistry ,Photoemission spectroscopy ,Inverse photoemission spectroscopy ,Angle-resolved photoemission spectroscopy ,Position and momentum space ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,Topological insulator ,0103 physical sciences ,Atomic physics ,010306 general physics ,0210 nano-technology ,Electronic band structure - Abstract
Angle-resolved photoelectron spectroscopy (ARPES) is widely used to study the electronic structure of crystalline solids such as high-temperature superconductors, topological insulators and graphene-based materials. Time-resolved ARPES has opened the door to the study of the response of such electronic features on ultrafast timescales. Now Rohwer et al. add a new dimension. Using high photon energies, they are able to study ultrafast dynamics at high momenta, at which some of the most interesting fundamental phenomena occur. Applying the technique to the charge density wave material 1T-TiSe2, they obtain stroboscopic images of the electronic band structure at high momentum and show that atomic-scale periodic long-scale order collapses on a surprisingly short timescale of 20 femtoseconds. This work reveals rapid response times in photoinduced properties that could stimulate research into new types of ultrafast switching device. Angle-resolved photoemission spectroscopy (ARPES) is widely used to study the electronic structure of a wide range of correlated materials. Time-resolved ARPES allows the study of the response of such electronic features on ultrafast timescales; this paper now adds an exciting new dimension by using high photon energies that allow the study of ultrafast dynamics at high momenta, where often the most interesting fundamental phenomena occur. The technique is applied to the charge density wave material 1T-TiSe2 and it is shown with stroboscopic imaging of the electronic band structure at high momentum that atomic-scale periodic long-range order collapses on a surprisingly short timescale of 20 femtoseconds. Intense femtosecond (10−15 s) light pulses can be used to transform electronic, magnetic and structural order in condensed-matter systems on timescales of electronic and atomic motion1,2,3. This technique is particularly useful in the study4,5 and in the control6 of materials whose physical properties are governed by the interactions between multiple degrees of freedom. Time- and angle-resolved photoemission spectroscopy is in this context a direct and comprehensive, energy- and momentum-selective probe of the ultrafast processes that couple to the electronic degrees of freedom7,8,9,10. Previously, the capability of such studies to access electron momentum space away from zero momentum was, however, restricted owing to limitations of the available probing photon energy10,11. Here, using femtosecond extreme-ultraviolet pulses delivered by a high-harmonic-generation source, we use time- and angle-resolved photoemission spectroscopy to measure the photoinduced vaporization of a charge-ordered state in the potential excitonic insulator 1T-TiSe2 (refs 12, 13). By way of stroboscopic imaging of electronic band dispersions at large momentum, in the vicinity of the edge of the first Brillouin zone, we reveal that the collapse of atomic-scale periodic long-range order happens on a timescale as short as 20 femtoseconds. The surprisingly fast response of the system is assigned to screening by the transient generation of free charge carriers. Similar screening scenarios are likely to be relevant in other photoinduced solid-state transitions and may generally determine the response times. Moreover, as electron states with large momenta govern fundamental electronic properties in condensed matter systems14, we anticipate that the experimental advance represented by the present study will be useful to study the ultrafast dynamics and microscopic mechanisms of electronic phenomena in a wide range of materials.
- Published
- 2010
30. Spectroscopy and population decay of a van der Waals gap state in layeredTiSe2
- Author
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M. Wiesenmayer, Michael Bauer, F. Steeb, S. Hilgenfeldt, Stefan Mathias, and Timm Rohwer
- Subjects
education.field_of_study ,Materials science ,Inverse photoemission spectroscopy ,Population ,chemistry.chemical_element ,Electronic structure ,Decoupling (cosmology) ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Crystal ,symbols.namesake ,chemistry ,Physics::Atomic and Molecular Clusters ,symbols ,Atomic physics ,van der Waals force ,education ,Spectroscopy ,Titanium - Abstract
Two-photon photoemission 2PPE spectroscopy is used to map the momentum-dependent energy distribution of unoccupied bands in the layered 1T-TiSe2 transition-metal dichalcogenide compound. A comparison of the experimental results with previous calculations based on the local-density functional approach enables us to identify the second Ti 3d conduction band and a localized unoccupied state that we assign to the presence of excess titanium atoms in the van der Waals gap of the crystal. Time-resolved 2PPE measurements show clear differences in the lifetime between the two states, indicative for the decoupling of the Ti excess atoms from the bulk electronic structure.
- Published
- 2010
31. CDW-superlattice suppression probed in time-resolved XUV-photoemission at the border of the Brillouin zone
- Author
-
Timm Rohwer, Bartosz Slomski, A. Stange, Michael Bauer, Kai Rossnagel, M. Wiesenmayer, S. Hellmann, C. Sohrt, and Lutz Kipp
- Subjects
Physics ,Condensed matter physics ,business.industry ,Superlattice ,Phase (waves) ,Brillouin zone ,Optics ,Condensed Matter::Superconductivity ,Extreme ultraviolet ,Condensed Matter::Strongly Correlated Electrons ,Transient (oscillation) ,Time-resolved spectroscopy ,business ,Ultrashort pulse ,Charge density wave - Abstract
Time- and angle-resolved XUV-photoemission at the border of the first Brillouin zone is employed to monitor the ultrafast suppression of a (2×2×2) reconstruction characteristic for the charge density wave (CDW) phase in 1T-TiSe2. The correlation of lattice dynamics and transient electronic response, which is probed in this experiment in parallel, provides new insights into the puzzling nature of the CDW mechanism in 1T-TiSe2.
- Published
- 2010
32. A direct view onto the carrier dynamics in graphite at the H point
- Author
-
Michael Bauer, Kai Rossnagel, Timm Rohwer, A. Stange, Lutz Kipp, C. Sohrt, S. Hellmann, and G. Rohde
- Subjects
Physics ,QC1-999 ,Nanotechnology ,Electrolyte ,Electron ,Condensed Matter::Materials Science ,Adsorption ,Chemical physics ,Excited state ,Ultrafast laser spectroscopy ,Graphite ,Physics::Chemical Physics ,Porosity ,Spectroscopy - Abstract
The photophysics of charge transfer between the electron donating, surface adsorbed D149 dye and an electron accepting porous ZnO film was investigated by measuring excited state lifetimes using ultrafast transient absorption spectroscopy. We systematically varioed the production scheme of the sample including the electrolyte.
- Published
- 2013
33. Time-domain evidence for an excitonic insulator
- Author
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S. Hellmann, Michael Bauer, Margaret M. Murnane, M. Kalläne, Timm Rohwer, Adra Carr, Kai Rossnagel, Henry C. Kapteyn, Lutz Kipp, and K. Hanff
- Subjects
Condensed Matter::Quantum Gases ,Physics ,Condensed matter physics ,Chemical physics ,Photoemission spectroscopy ,QC1-999 ,Condensed Matter::Strongly Correlated Electrons ,Time domain ,Insulator (genetics) - Abstract
Time- and angle-resolved photoemission spectroscopy with a high–harmonic- generation source is used to classify the potential excitonic insulator 1T -TiSe2 and the reference Peierls-Mott insulator 1T -TaS2 on the basis of the melting times of “spectroscopic order parameters”.
- Published
- 2013
34. All-optical three-dimensional electron pulse compression.
- Author
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Byron Freelon, Timm Rohwer, Steven G Johnson, Nuh Gedik, and Liang Jie Wong
- Subjects
- *
ELECTRONIC pulse techniques , *ATTOSECOND pulses , *PICOSECOND pulses , *ULTRASHORT laser pulses , *MAGNETIC lenses - Abstract
We propose an all-optical, three-dimensional electron pulse compression scheme in which Hermite–Gaussian optical modes are used to fashion a three-dimensional optical trap in the electron pulse’s rest frame. We show that the correct choices of optical incidence angles are necessary for optimal compression. We obtain analytical expressions for the net impulse imparted by Hermite–Gaussian free-space modes of arbitrary order. Although we focus on electrons, our theory applies to any charged particle and any particle with non-zero polarizability in the Rayleigh regime. We verify our theory numerically using exact solutions to Maxwell’s equations for first-order Hermite–Gaussian beams, demonstrating single-electron pulse compression factors of in both longitudinal and transverse dimensions with experimentally realizable optical pulses. The proposed scheme is useful in ultrafast electron imaging for both single- and multi-electron pulse compression, and as a means of circumventing temporal distortions in magnetic lenses when focusing ultrashort electron pulses. Other applications include the creation of flat electron beams and ultrashort electron bunches for coherent terahertz emission. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
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