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Letteratura scientifica selezionata sul tema "Ultrafast current"

Autore: Grafiati

Pubblicato: 22 febbraio 2025

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Articoli di riviste sul tema "Ultrafast current"

Lu Wen-Tian, Yao Chun-Wei, YAN Zhi e YUAN Zhe. "Ultrafast Spin Dynamics Research on Laser-Induced Spin Valve Structures". Acta Physica Sinica 74, n. 6 (2025): 0. https://doi.org/10.7498/aps.74.20241744.

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The discovery of ultrafast demagnetization has introduced a new approach for generating ultrafast spin currents using an ultrashort laser, potentially enabling faster manipulation of material magnetism. This has sparked research into the transport mechanisms of ultrafast spin currents. However, the underlying processes remain poorly understood, particularly the factors influencing interlayer spin transfer. This study employs a superdiffusive spin transport model to investigate the ultrafast spin transport mechanisms in the Ni/Ru/Fe spin valve system, with a particular focus on how interlayer spin transfer affects the ultrafast magnetization dynamics of the ferromagnetic layer. First, by calculating the laser-induced magnetization dynamics of the Ni/Ru/Fe system under different magnetization alignments, the study validates recent experimental findings. Further analysis reveals that reducing the thickness of the Ru spacer layer significantly enhances the spin current intensity and increases the demagnetization difference in the Fe layer, confirming the key role of the hot electron spin current generated by the Ni layer in interlayer spin transport. Additionally, the spin decay length of hot electron spin currents in the spacer Ru layer is determined to be approximately 0.5 nm. This study also shows that laser-induced transient magnetization enhancement can be achieved by adjusting the relative laser absorption in the films. These results provide theoretical support for the future ultrafast magnetic control of spin valve structures and contribute to the advancement of spintronics in high-speed information processing and storage applications.

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Sotome, M., M. Nakamura, J. Fujioka, M. Ogino, Y. Kaneko, T. Morimoto, Y. Zhang et al. "Spectral dynamics of shift current in ferroelectric semiconductor SbSI". Proceedings of the National Academy of Sciences 116, n. 6 (22 gennaio 2019): 1929–33. http://dx.doi.org/10.1073/pnas.1802427116.

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Photoexcitation in solids brings about transitions of electrons/holes between different electronic bands. If the solid lacks an inversion symmetry, these electronic transitions support spontaneous photocurrent due to the geometric phase of the constituting electronic bands: the Berry connection. This photocurrent, termed shift current, is expected to emerge on the timescale of primary photoexcitation process. We observe ultrafast evolution of the shift current in a prototypical ferroelectric semiconductor antimony sulfur iodide (SbSI) by detecting emitted terahertz electromagnetic waves. By sweeping the excitation photon energy across the bandgap, ultrafast electron dynamics as a source of terahertz emission abruptly changes its nature, reflecting a contribution of Berry connection on interband optical transition. The shift excitation carries a net charge flow and is followed by a swing over of the electron cloud on a subpicosecond timescale. Understanding these substantive characters of the shift current with the help of first-principles calculation will pave the way for its application to ultrafast sensors and solar cells.

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Kiemle, Jonas, Philipp Zimmermann, Alexander W. Holleitner e Christoph Kastl. "Light-field and spin-orbit-driven currents in van der Waals materials". Nanophotonics 9, n. 9 (29 giugno 2020): 2693–708. http://dx.doi.org/10.1515/nanoph-2020-0226.

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AbstractThis review aims to provide an overview over recent developments of light-driven currents with a focus on their application to layered van der Waals materials. In topological and spin-orbit dominated van der Waals materials helicity-driven and light-field-driven currents are relevant for nanophotonic applications from ultrafast detectors to on-chip current generators. The photon helicity allows addressing chiral and non-trivial surface states in topological systems, but also the valley degree of freedom in two-dimensional van der Waals materials. The underlying spin-orbit interactions break the spatiotemporal electrodynamic symmetries, such that directed currents can emerge after an ultrafast laser excitation. Equally, the light-field of few-cycle optical pulses can coherently drive the transport of charge carriers with sub-cycle precision by generating strong and directed electric fields on the atomic scale. Ultrafast light-driven currents may open up novel perspectives at the interface between photonics and ultrafast electronics.

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Cottrell, W. J., T. G. Ference e K. A. Puzey. "Improved magnetooptic modulator for ultrafast current pulses". IEEE Photonics Technology Letters 14, n. 5 (maggio 2002): 624–26. http://dx.doi.org/10.1109/68.998705.

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Lian, Meng, e Jie Wu. "Ultrafast micropumping by biased alternating current electrokinetics". Applied Physics Letters 94, n. 6 (9 febbraio 2009): 064101. http://dx.doi.org/10.1063/1.3080681.

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Kim, Un-Tae, Myeong-Hun Jo e Hyo-Jin Ahn. "Microgrid-Patterned Ni Foams as Current Collectors for Ultrafast Energy Storage Devices". Metals 14, n. 3 (19 marzo 2024): 354. http://dx.doi.org/10.3390/met14030354.

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Current research is focused on developing active materials through surface functionalization, porosity, composites, and doping for ultrafast electric double layer capacitors (EDLCs). In this study, deviating from existing strategies focused on active materials, we designed tunable 3D microgrid-patterned (MP) surface morphologies on Ni foams used as current collectors using SUS meshes as rigid stamps during roll pressing. The surface geometries of the MP-Ni foams were controlled to standard mesh scales of 24, 40, and 60 (denoted as 24MP-Ni, 40MP-Ni, and 60MP-Ni, respectively). The three MP-Ni samples with different microgrid sizes presented different surface geometries, such as root-mean-square roughness (Rrms), skewness roughness (Rsk), and width/depth scales of the microgrid patterns. Consequently, 40MP-Ni demonstrated an optimized surface geometry with high Rrms (35.4 μm) and Rsk (−0.19) values, which facilitated deep slurry infiltration and increased its contact area with the active material. Surface optimization of the MP-Ni enabled ultrafast and reversible charge transport kinetics owing to its relaxed electron transfer resistance and robust adhesion to the active material compared with bare Ni foam. EDLC electrodes with 40MP-Ni achieved an ultrafast-rate capability (96.0 F/g at 20 A/g) and ultrafast longevity (101.9% capacity retention after 5000 cycles at 5 A/g) without specific modification of active material.

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Sobacchi, Emanuele, Tsvi Piran e Luca Comisso. "Ultrafast Variability in AGN Jets: Intermittency and Lighthouse Effect". Astrophysical Journal Letters 946, n. 2 (1 aprile 2023): L51. http://dx.doi.org/10.3847/2041-8213/acc84d.

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Abstract Gamma-ray flares from active galactic nuclei (AGNs) show substantial variability on ultrafast timescales (i.e., shorter than the light-crossing time of the AGN’s supermassive black hole). We propose that ultrafast variability is a by-product of the turbulent dissipation of the jet Poynting flux. Due to the intermittency of the turbulent cascade, the dissipation is concentrated in a set of reconnecting current sheets. Electrons energized by reconnection have a strong pitch-angle anisotropy, i.e., their velocity is nearly aligned with the guide magnetic field. Then each current sheet produces a narrow radiation beam, which dominates the emission from the whole jet when it is directed toward the observer. The ultrafast variability is set by the light-crossing time of a single current sheet, which is much shorter than the light-crossing time of the whole emission region. The predictions of our model are (i) the bolometric luminosity of ultrafast AGN flares is dominated by the inverse Compton (IC) emission as the lower-energy synchrotron emission is suppressed due to the pitch-angle anisotropy; (ii) if the observed luminosity includes a nonflaring component, the variations of the synchrotron luminosity have a small amplitude; and (iii) the synchrotron and IC emission are less variable at lower frequencies, as the cooling time of the radiating particles exceeds the light-crossing time of the current sheet. Simultaneous multiwavelength observations of ultrafast AGN flares can test these predictions.

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Zymmer, K., e P. Mazurek. "Comparative investigation of SiC and Si power electronic devices operating at high switching frequency". Bulletin of the Polish Academy of Sciences: Technical Sciences 59, n. 4 (1 dicembre 2011): 555–59. http://dx.doi.org/10.2478/v10175-011-0068-0.

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Comparative investigation of SiC and Si power electronic devices operating at high switching frequencyThe paper presents results of measurements of the reverse recovery current and dynamic forward voltage of the silicon carbide (SiC) Schottky diodes operating at a 500 A/μs current slope. These data were compared with the corresponding parameters determined for ultrafast silicon (Si) diodes. Results of power losses measurement in SiC Schottky diodes operating at switching frequency range of (10-200) kHz are presented and compared with corresponding data of ultrafast Si diodes. Also, results of power losses measurements in transistors of dc voltage switch are shown. Investigations were conducted with a SiC and the ultrafast Si freewheeling diode at the transistor switching frequency of 100 kHz. The results of measuring power losses dissipated in the dc converter with a SiC Schottky diode and the ultrafast silicon diode are also presented.

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Elezzabi, A. Y., e M. R. Freeman. "Ultrafast magneto‐optic sampling of picosecond current pulses". Applied Physics Letters 68, n. 25 (17 giugno 1996): 3546–48. http://dx.doi.org/10.1063/1.116632.

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Wagner, Ronald S., Jeffrey M. Bradley, Carl J. Maggiore, Jerome G. Beery e Robert B. Hammond. "An Approach to Measure Ultrafast-Funneling-Current Transients". IEEE Transactions on Nuclear Science 33, n. 6 (1986): 1651–56. http://dx.doi.org/10.1109/tns.1986.4334658.

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Più fonti

Tesi sul tema "Ultrafast current"

Wei, Jiaqi. "Magnetization manipulation induced by spin current and ultrafast laser". Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0121.

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La manipulation de l’aimantation est un des sujets de recherche les plus étudiés dans le domaine de l’électronique de spin. Différentes méthodes de manipulations peuvent exciter les propriétés dynamiques de l’aimantation à différentes échelles de temps. Parmi les phénomènes dynamiques, la précession de l’aimantation et la désaimantation ultrarapide ont suscité un intérêt particulier. La fréquence de précession de l’aimantation est de l’ordre du GHz et correspond à une période de centaines de picosecondes. Cette précession est le mécanisme à l’œuvre dans les nano-oscillateurs à transfert de spin (NOTS), un nouveau type de dispositif microonde présentant des avantages sur l’oscillateur commandé en tension (OCT) conventionnel en termes de taille, de consommation d’énergie et d’adaptabilité de la fréquence. La désaimantation ultrarapide a été observé pour la première fois dans du nickel en quelques centaines de femtosecondes. Le renversement tout optique (RTO), nécessitant la désaimantation ultrarapide, a ensuite été démontré expérimentalement. Le RTO est bien plus rapide que tout autre retournement de l’aimantation par couple et est donc prometteur pour construire des mémoires magnétiques ultrarapides. Bien que de nombreuses études sur ces deux phénomènes existent, plusieurs problèmes se doivent d’être résolus avant de pouvoir passer à l’étape de production industrielle. Les NOTS sont censés être utilisés pour la modulation par déplacement d’amplitude (MDA) ou la modulation par déplacement de fréquence (MDF), mais les conditions optimales pour ces deux types de modulation microondes n’ont pas encore été assez investiguées. Quant au RTO, l’influence des paramètres du laser tels que la fluence ou la durée de l’impulsion et des propriétés du matériau tels que le composition et l’épaisseur n’a pas fait l’objet d’études systématique. Dans ce manuscrit, ces deux types de manipulation de l’aimantation sont étudiés en détail. En ce qui concerne la précession de l’aimantation, nous démontrons qu’un champ magnétique accru permet d’obtenir une plus large plage de fréquence possible alors qu’un champ magnétique plus faible résulte en une plage d’amplitude possible élargie. Ainsi ces deux scenarii sont applicables au MDF et MDA, respectivement, et posent les bases d’une utilisation des NOTS en modulation microonde. Dans la deuxième étude, nous démontrons que le RTO dépends fortement des caractéristiques de l’impulsion laser. Pour cela nous avons construit un diagramme d’état pour le GdFeCo et le Co/Pt, deux matériaux typiques respectivement du retournement tout optique indépendant de l’hélicité (RTO-IH) et du retournement tout optique dépendant de l’hélicité (RTO-DH). Ces résultats permettent une meilleure compréhension du mécanisme fondamental régissant la dynamique de l’aimantation induite par exposition à un laser
Magnetization manipulation is one of the most actively researched topics in the field of spintronics. Different ways of manipulation can trigger magnetization dynamics on different time scales. Among these dynamics, magnetization precession and ultrafast demagnetization have attracted substantial interests. The frequency of magnetization precession is normally in the GHz range corresponding to a period of hundreds of ps, which is the basic mechanism of spin torque nano-oscillators (STNO), a new type of microwave devices which show advantages over conventional voltage-controlled oscillator (VCO) in terms of size, energy consumption and tunable frequency. Ultrafast demagnetization was first observed in Ni which takes places in hundreds of femtoseconds. Triggered by this, All-Optical Switching (AOS) was then demonstrated which is much faster than any torque induced switching, promising for application in the high-speed magnetic memory. Although many studies on these two phenomena have been reported, several issues need to be addressed before they move toward application. STNOs are supposed to be used for amplitude shift keying (ASK) or frequency shift keying (FSK), but the optimal conditions for these two types of microwave modulation are still not well explored. As for AOS, the influence of the laser parameters such as fluence and pulse duration and the material properties such as the composition and the thickness has not been systematically investigated. In this thesis, these two types of magnetization manipulation are studied in detail. Concerning magnetization precession, we demonstrate that a stronger magnetic field allows a wider frequency tuning range while a smaller magnetic field results in a wider amplitude tuning range. Thus, these two scenarios are applicable to FSK and ASK, respectively, providing guidelines for STNO in microwave modulation. In the second study, we demonstrate that AOS depends strongly on pulse characteristic. This was shown by building a magnetization state diagram for GdFeCo and Co/Pt which are two typical materials showing All-Optical Helicity-Independent Switching (AO-HIS) and All-Optical Helicity-Dependent Switching (AO-HDS), respectively. These results allow a better understanding of the fundamental mechanism behind laser-induced magnetization dynamics

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Bubelnik, Matthew. "THE EFFECTS OF ELECTRODE GEOMETRY ON CURRENT PULSE CAUSED BY ELECTRICAL DISCHARGE OVER AN ULTRA-FAST LASER FILAMENT". Master's thesis, University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3695.

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The time-resolved electrical conductivity of a short-pulse generated plasma filament in air was studied. Close-coupled metal electrodes were used to discharge the stored energy of a high-voltage capacitor and the resulting microsecond-scale electrical discharge was measured using fast current sensors. Significant differences in the time dependence of the current were seen with the two electrode geometries used. Using sharp-tipped electrodes additional peaks in the time-resolved conductivity were seen, relative to the single peak seen with spherical electrodes. We attribute these additional features to secondary electron collisional ionization brought about by field enhancement at the tips. Additional discrepancies in the currents measured leaving the high-voltage electrode and that returning to ground were also observed. Implications for potential laser-induced discharge applications will be discussed.
M.S.
Other
Optics and Photonics
Optics

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Mohamad, Haidar Jawad. "Ultrafast optical measurements of spin-polarized electron dynamics in nanostructured magnetic materials". Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/18425.

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At present, electronic devices depend upon electric charge to transfer and record information. However, such devices are approaching a scaling limit due to Joule heating. Spintronics offers a solution by exploiting the spin rather than the charge of the electron, since the propagation of spin current can in principle occur without dissipation. Immediate applications lie in magnetic random access memory and novel media for hard disk recording. Within this thesis, the Magneto-optical Kerr effect (MOKE) has been used to measure the static and dynamic magnetic properties of a number of different thin film samples that are of interest for spintronic applications. A femtosecond laser has been used to perform time-resolved MOKE (TRMOKE) and time resolved reflectivity (TRR) measurements simultaneously, which probe the spin and charge dynamics respectively. Measurements have been performed upon a continuous thin film of CrO2 that is known to be half-metallic in bulk form, and a series of YIG/Cu/Ni81Fe19 based structures that are expected to exhibit the spin Seebeck effect (SSE). Chemical vapour deposition (CVD) was used to fabricate the continuous CrO2 thin film on a (100)-oriented TiO2 substrate. Precessional magnetisation dynamics were studied by means of the TRMOKE technique. The dependence of the precession frequency and the effective damping parameter upon the static applied magnetic field were investigated. The precession frequency exhibited a minimum at the hard axis saturation field as expected. However precession was also observed for fields greater than the hard axis saturation value, perhaps suggesting the presence of a twisted magnetic state within the film. TRMOKE and TRR measurements were performed upon the YIG/Cu/Ni81Fe19 based structures for different values of the pump fluence and applied magnetic field. For fixed pump fluence and varying applied field, the frequency of precession is well described by a numerical solution of the Landau-Lifshitz equation for the Ni81Fe19 (permalloy, Py) layer. The frequency, amplitude, damping, phase and chirp of the precessional oscillations was extracted from measurements made with a field of 3 kOe applied at 2.8° from the normal to the sample plane, in a configuration designed to maximise any spin transfer torque (STT) generated by the SSE. The oscillation parameters extracted for trilayer samples and a Py reference sample were found to be very similar. Features indicative of STT predicted by simulations were not observed. This suggests that either the YIG/Cu interface was unable to efficiently transmit spin current within the samples studied here, or else that the STT generated by means of the SSE is too small to be of practical use.

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Hurst, Jerome. "Ultrafast spin dynamics in ferromagnetic thin films". Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAE004/document.

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Dans cette thèse, on s’intéresse à l'étude théorique et à la simulation numérique de la dynamique de charges et de spins dans des nano-structures métalliques. Ces dernières années la physique des nano-structures métalliques à connu un intérêt croissant, aussi bien d'un point de vue de la physique fondamental que d'un point de vue des applications technologiques. Il est donc essentiel d'avoir des modèles théoriques nous permettant de décrire correctement ce type d'objets. Cette thèse comporte deux études distinctes. Dans un premier temps on utilise un modèle semi-classique dans l'espace des phases afin d'étudier la dynamique de charges et de spins dans des films ferromagnétiques(Nickel). On décrit dans le même modèle le magnétisme itinérant et le magnétisme localisé. On montre qu'il est possible, en excitant le système avec un laser pulsé femtoseconde dans le domaine du visible, de créer un courant de spin oscillant dans la direction normal du film sur des temps ultrarapides(femtoseconde). Dans un second temps on s’intéresse à la dynamique de charge d'électrons confinés dans des nano-particules d'Or ou bien encore par des potentiels anisotropes. On montre que de telles systèmes sont des candidats intéressant pour faire de la génération d'harmoniques
In this thesis we focus on the theoritical description and on the numerical simulation of the charge and spin dynamics in metallic nano-structures. The physics of metallic nano-structures has stimulated a huge amount of scientific interest in the last two decades, both for fundamental research and for potential technological applications. The thesis is divided in two parts. In the first part we use a semiclassical phase-space model to study the ultrafast charge and spin dynamics in thin ferromagnetic films (Nickel). Both itinerant and localized magnetism are taken into account. It is shown that an oscillating spin current can be generated in the film via the application of a femtosecond laser pulse in the visible range. In the second part we focus on the charge dynamics of electrons confined in metallic nano-particles (Gold) or anisotropic wells. We show that such systems can be used for high harmonic generation

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Abdul, Hadi Zeinab. "Terahertz emission spectroscopy of multiferroic bismuth ferrite : insights into ultrafast currents and phonon dynamics". Electronic Thesis or Diss., Le Mans, 2024. http://www.theses.fr/2024LEMA1030.

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La technologie térahertz (THz) a suscité un intérêt significatif dans la communauté scientifique en raison de sa position unique dans le spectre électromagnétique, complétant le gap entre les régions des micro-ondes et de l'infrarouge. Cette radiation est non ionisante et peut pénétrer divers matériaux sans les endommager, ce qui la rend très attirante pour de nombreuses applications potentielles. Les avancées récentes dans la technologie des lasers ultra-rapides ont élargi l'exploration du rayonnement THz à un large éventail de technologies passionnantes. Elle est désormais utilisée dans des domaines tels que la médecine pour de nouvelles techniques d'imagerie, en spectroscopie pour l'analyse des matériaux, dans les technologies de l'information et de la communication pour le transfert de données plus rapide, et même dans la sécurité, l'agriculture, le contrôle de qualité et la science des matériaux fondamentaux.Par conséquent, le développement de sources THz efficaces et réglables est devenu un défi au sein de la communauté THz pour développer davantage ces applications, motivant l'exploration de nouveaux matériaux et mécanismes d'émission THz. Dans mon projet de doctorat, j'ai exploré un nouvel émetteur THz : le matériau multiferroïque le plus connu, le ferrite de bismuth (BiFeO3). Ce matériau multiferroïque est particulièrement intéressant en raison de ses propriétés multiferroïques distinctives. Le BiFeO3 présente à la fois une large polarisation ferroélectrique et un ordre antiferromagnétique à température ambiante, offrant une interaction unique des ordres ferroélectriques et magnétiques et faisant de ce matériau un candidat prometteur pour la génération de THz.En utilisant un montage de spectroscopie d'émission THz que j'ai construit, avec sa détection électro-optique, j'examine l'émission THz de trois échantillons de BiFeO3 distincts. Le premier avec une polarisation dans le plan, un autre avec une polarisation hors plan, et un troisième présentant deux domaines avec deux différentes orientations de polarisation. Cette technique permet l'observation et l'analyse directes du rayonnement THz émis par ces échantillons suite à l'excitation laser au-dessus du gap.Les études expérimentales impliquent une analyse détaillée des signaux THz émis par les échantillons de BiFeO3 dans des conditions expérimentales variées. En variant les longueurs d'onde de la pompe, les orientations des échantillons, les directions de polarisation de la lumière de la pompe, et la puissance de la pompe, nous pouvons explorer comment ces facteurs influencent l'émission THz. Ensuite, nous séparent la dynamique ultra-rapide des porteurs (courant ultra-rapide) et les vibrations du réseau (phonons optiques) contribuant à ce signal THz émis. Enfin, en analysant leur réponse aux changements des paramètres expérimentaux, nous pouvons approfondir notre compréhension des mécanismes physiques contribuant à ces dynamiques ultra-rapides et à l'émission THz dans BiFeO3
Terahertz (THz) technologies have attracted significant interest in the scientific community due to their unique position in the electromagnetic spectrum, bridging the gap between the microwave and infrared regions. This radiation is non-ionizing and can penetrate various materials without causing damage, making it highly attractive for numerous potential applications. Recent advances in ultrafast laser technology have expanded the exploration of THz radiation into a wide range of exciting technologies. It’s now being used in fields like medicine for new imaging techniques, in spectroscopy for analyzing materials, in information and communication technology for faster data transfer, and even in security, agriculture, quality control and fundamental material science. Consequently, the development of efficient and tunable THz sources has become a major focus within the THz community to expand these applications further, motivating the exploration of new materials and emission mechanisms. In my PhD project, I have explored a promising new THz emitter: the well-known multiferroic material ‘Bismuth Ferrite’ (BiFeO3). This multiferroic material is particularly interesting due to its distinctive multiferroic properties. BiFeO3 exhibits both a large ferroelectric polarization and a antiferromagnetic order at room temperature offering a unique interplay of ferroelectric and magnetic orders and making this material a promising candidate for THz generation. Using a THz emission spectroscopy setup that I constructed, with its electro-optical sampling detection, I examine THz emission from three distinct BiFeO3 samples. First one with in-plane polarization, another with out-of-plane polarization, and a third presenting striped domains with two orientations of polarization. This technique allows for the direct observation and analysis of THz radiation emitted by these samples upon above gap laser excitation. The experimental investigation involves a detailed study of the THz transient signals emitted from the BiFeO3 samples under varying experimental conditions. By varying the pump wavelengths, sample orientations, directions of pump light polarization, and pump power levels, we can explore how these factors influence the THz emission. Following this, we extract the carrier dynamics (ultrafast current) and lattice vibrations (optical phonons) contributions to this THz transient. And finally, by analyzing their response to experimental parameters changes, we can have a deeper understanding of the physical mechanisms contributing to these ultrafast dynamics and THz emission in BiFeO3

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Welsh, Gregor H. "Understanding and control of ultrafast currents for terahertz generation". Thesis, University of Strathclyde, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.487861.

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Development of terahertz pulse sources and methods are ongoing with an urge to reduce cost, increase quality of emitter design and improve on the output power. This thesis details two advances made in creating terahertz pulses from ultrafast currents, the first is optimising the biasing method used on photoconductive antennas for terahertz emission and the second manufacturing and studying electron-emission type terahertz emitters.

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Barnes, Mark. "Terahertz emission from ultrafast lateral diffusion currents within semiconductor devices". Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/363127/.

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Single cycle THz emission from unbiased semiconductor devices after ultrafast carrier excitation can be attributed to surge currents on the surface of the device. These currents are due to either drift currents where carriers are accelerated by an internal electric field perpendicular to the surface (surface field effect) or diffusion currents where a separation of charge forms due to electrons and holes having different mobilities (photo-Dember effect). This surface emission is difficult to out couple from the semiconductor device as the emission is parallel to the surface of the semiconductor. This difficulty in out coupling led to a decline in interest for these types of emitters in preference to photoconductive emitters which today are the standard type of emitters used in THz time domain spectroscopy. In recent years a new type of surface emitter based on lateral diffusion currents (lateral Dember currents) has been proposed and demonstrated. This work acted as the initial inspiration for the work described within this thesis. The emission was attributed to net diffusion currents that formed from an initially asymmetrical carrier distribution that formed due to partially masking the pump spot with a metal mask. Simulations of the situation revealed that diffusion alone cannot account for the observed THz emission from these devices. From this I have extended the mechanism taking into account lateral diffusion currents and dipole suppression under a metal mask. Along with theoretical arguments experimental evidence is given that supports this new theory. These devices are further explored experimentally giving insights into the nature of the emission and how it depends on different pump parameters and external electric fields. Based on this new interpretation I present the design, fabrication, and testing of multiplex emitters that are are comparable with commercial photoconductive emitters in both power and band-width.

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Remy, Quentin. "Ultrafast spin dynamics and transport in magnetic metallic heterostructures". Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0191.

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Le contrôle de l'aimantation, et donc du spin, aux échelles de temps ultra courtes, est un sujet d'importance fondamentale pour l'élaboration de systèmes qui peuvent stocker de l'information beaucoup plus rapidement. La possibilité d'écrire de l'information avec des pulses laser femtoseconde sur des métaux magnétiques tels que GdFeCo ou MnRuGa en quelques picosecondes fut une étape conséquente pour pouvoir réaliser ce progrès technologique. Cependant, le renversement de l'aimantation observé dans ces matériaux après les avoir irradié avec un unique pulse laser, appelé retournement tout optique indépendant de l'hélicité (AO-HIS pour {All Optical Helicity Independent Switching} en anglais), est toujours limité à une petite catégorie de matériaux ferrimagnétiques et sa description physique n'est toujours pas entièrement comprise. Dans cette thèse, nous étudions l'AO-HIS dans des films minces composés d'une ou deux couches d'alliages de GdFeCo de différentes compositions. Nous montrons que ces couches génèrent des courants de spin qui peuvent modifier l'AO-HIS de ces matériaux. En particulier, nous montrons qu'il est possible d'utiliser ces courants de spin pour renverser l'aimantation des différentes multicouches ferromagnétiques, avec un seul pulse laser femtoseconde, qui ne subiraient qu'une désaimantation et ne se retourneraient donc pas autrement. En changeant la composition de l'alliage de GdFeCo et la température de Curie du matériau ferromagnétique, nous pouvons modifier l'énergie nécessaire pour engendrer le renversement magnétique de la multicouche ferromagnétique avec un pulse de lumière. De plus, nous montrons que l'AO-HIS de l'alliage de GdFeCo n'est en réalité pas nécessaire ainsi que l'illumination directe de la couche ferromagnétique par la lumière laser. Il est donc possible de retourner l'aimantation d'un matériau ferromagnétique en utilisant uniquement des courants ultra courts de chaleur et de spin qui sont créés par la désaimantation ultra rapide partielle de l'alliage de GdFeCo et transportés jusqu'à la couche ferromagnétique via une couche de cuivre. Ces expériences sont comprises grâce à un modèle de transport semi classique dans un système contenant des électrons, des phonons et des spins quantiques et qui est basé sur l'échange de moment cinétique entre des spins localisés et itinérants. Enfin, nous avons mesuré la dynamique du renversement de l'aimantation de ce système ferromagnétique. Nous montrons que ce retournement se passe en moins d'une picoseconde, ce qui est le retournement d'aimantation le plus rapide jamais observé. Nous montrons que le courant de spin provenant de l'alliage de GdFeCo à un pouvoir réfrigérant sur l'aimantation, déjà visible en moins d'une picoseconde, et qui peut augmenter l'aimantation transitoire du système jusqu'à trente pourcents. Ces résultats sont également compris dans le cadre de notre modèle de transport de chaleur et de moment cinétique
The control of magnetization, and thus spin, at the shortest timescale, is a fundamental subject for the development of faster data storage devices. The capability to encode information with femtosecond laser pulses on magnetic metals such as GdFeCo or MnRuGa within a few picoseconds was a significant step towards the realization of such a technology. However, the reversal of magnetization observed in these materials upon a single laser pulse irradiation, called All Optical Helicity Independent Switching (AO-HIS), is still limited to a small class of ferrimagnetic materials and its physical mechanism is not completely understood.In this work, we study AO-HIS in magnetic thin films composed of a single or two GdFeCo layers with different alloy compositions. We show that these layers generate spin currents that can affect the AO-HIS of these materials. In particular, we can use such spin currents to reverse the magnetization of various ferromagnetic multilayers, with a single femtosecond laser pulse, which would otherwise only demagnetize and never switch. Playing with the GdFeCo alloy concentration and the ferromagnetic multilayer Curie temperature, we can tune the energy required to observe single shot reversal of the ferromagnet. In addition, we show that neither AO-HIS of the GdFeCo layer is actually required nor direct light illumination of the ferromagnetic multilayer. It is then possible to reverse the magnetization of ferromagnets using only ultrashort heat and spin currents which are generated by the partial ultrafast demagnetization of GdFeCo and transported via a thick metallic copper spacer. These experimental results were successfully understood using semiclassical transport equations for electrons, phonons and quantum spins based on exchange of angular momentum between localized and itinerant spins.Finally, we were able to measure the dynamics of the ferromagnetic multilayer magnetization reversal which is shown to happen in less than a picosecond, being the fastest magnetization reversal ever observed. The action of the external spin current is shown to have an ultrafast cooling effect on the spin which is visible at the sub-picosecond timescale and which can enhance the transient magnetization by up to thirty percent. These results are also understood using our model of heat and angular momentum transport

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Sternemann, Elmar [Verfasser], Markus [Akademischer Betreuer] Betz e Torsten [Gutachter] Meier. "Ultrafast coherently controlled currents in GaAs: physics and applications / Elmar Sternemann. Betreuer: Markus Betz. Gutachter: Torsten Meier". Dortmund : Universitätsbibliothek Dortmund, 2015. http://d-nb.info/1110893809/34.

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Paasch-Colberg, Tim [Verfasser], Reinhard [Akademischer Betreuer] Kienberger e Peter A. [Akademischer Betreuer] Feulner. "Ultrafast, optical-field-induced currents in solid-state materials / Tim Paasch-Colberg. Gutachter: Peter A. Feulner ; Reinhard Kienberger. Betreuer: Reinhard Kienberger". München : Universitätsbibliothek der TU München, 2014. http://d-nb.info/1051078296/34.

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Libri sul tema "Ultrafast current"

Eriksson, Olle, Anders Bergman, Lars Bergqvist e Johan Hellsvik. Outlook on Magnetization Dynamics. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198788669.003.0012.

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Since its original formulation in the mid-1990's, atomistic spin-dynamics has become an important tool for modelling of dynamic processes in magnetic materials. So far this book has described current methodological methods and functionalities of atomistic spin-dynamics simulations. Applications of DFT and ASD techniques to selected topics have been presented in this book, for instance methods for calculation of the microscopic Heisenberg and Gilbert parameter from first principles (Chapters 2 and 6), multiscale modelling of magnon spectra in bulk and thin film magnets (Chapter 9), and theoretical investigations of ultrafast switching dynamics in ferromagnets and ferrimagnets (Chapter 10), and of exotic dynamics of topologically protected spin textures (Chapter 11). In this closing chapter we give an outlook on recent and anticipated developments of the methodology.

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Capitoli di libri sul tema "Ultrafast current"

Bauer, T., A. B. Hummel, J. S. Kolb, H. G. Roskos, Yu A. Kosevich e K. Köhler. "The Hall Current of Coherent Electron Wavepackets". In Ultrafast Phenomena XIII, 353–55. Berlin, Heidelberg: Springer Berlin Heidelberg, 2003. http://dx.doi.org/10.1007/978-3-642-59319-2_109.

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Pfeiffer, W. "Ultrafast Electrical Voltage and Current Monitors". In Fast Electrical and Optical Measurements, 145–74. Dordrecht: Springer Netherlands, 1986. http://dx.doi.org/10.1007/978-94-017-0445-8_7.

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Kraack, Jan Philip. "Ultrafast structural molecular dynamics investigated with 2D infrared spectroscopy methods". In Topics in Current Chemistry Collections, 113–205. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-030-02478-9_4.

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Münzenberg, M. "Spin-wave and spin-current dynamics in ultrafast demagnetization experiments". In Springer Proceedings in Physics, 86–88. Cham: Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-07743-7_28.

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Brundage, Bruce H. "What is the current role of ultrafast CT in coronary imaging?" In Developments in Cardiovascular Medicine, 531–44. Dordrecht: Springer Netherlands, 1996. http://dx.doi.org/10.1007/978-94-009-0291-6_40.

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Mahapatra, Susanta. "Quantum Molecular Dynamics on the Conically Intersecting Potential Energy Surfaces: Nonadiabatic Effects and Ultrafast Relaxation". In Current Developments in Atomic, Molecular, and Chemical Physics with Applications, 121–26. Boston, MA: Springer US, 2002. http://dx.doi.org/10.1007/978-1-4615-0115-2_16.

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Wijesinghe, Philip, e Kishan Dholakia. "Widefield Multiphoton Imaging at Depth with Temporal Focusing". In Neuromethods, 263–91. New York, NY: Springer US, 2023. http://dx.doi.org/10.1007/978-1-0716-2764-8_9.

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AbstractOptical imaging has the potential to reveal high-resolution information with minimal photodamage. The recent renaissance of super-resolution, widefield, ultrafast, and computational imaging methods has broadened its horizons even further. However, a remaining grand challenge is imaging at depth over a widefield and with a high spatiotemporal resolution. This achievement would enable the observation of fast collective biological processes, particularly those underpinning neuroscience and developmental biology. Multiphoton imaging at depth, combining temporal focusing and single-pixel detection, is an emerging avenue to address this challenge. The novel physics and computational methods driving this approach offer great potential for future advances. This chapter articulates the theories of temporal focusing and single-pixel detection and details the specific approach of TempoRAl Focusing microscopy with single-pIXel detection (TRAFIX), with a particular focus on its current practical implementation and future prospects.

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Avaria, G., M. Grisham, J. Li, F. G. Tomasel, V. N. Shlyapstsev, M. Busquet, M. Woolston e J. J. Rocca. "Ionization of Xenon to the Nickel-Like Stage and Beyond in Micro-Capillary Plasma Columns Heated by Ultrafast Current Pulses". In Springer Proceedings in Physics, 147–53. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-19521-6_19.

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Laman, N., D. Côté, J. E. Sipe e H. M. van Driel. "Femtosecond optically induced rectification, shift and injection currents in GaAs". In Ultrafast Phenomena XIII, 362–64. Berlin, Heidelberg: Springer Berlin Heidelberg, 2003. http://dx.doi.org/10.1007/978-3-642-59319-2_112.

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Yamanishi, M., M. Kurosaki, Y. Osaka e S. Datta. "Ultrafast Control of Quantum Interference Currents by Virtual Charge Polarizations in Biased Quantum Well Structures". In Ultrafast Phenomena VI, 334–36. Berlin, Heidelberg: Springer Berlin Heidelberg, 1988. http://dx.doi.org/10.1007/978-3-642-83644-2_94.

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Atti di convegni sul tema "Ultrafast current"

Postnikov, D. V., e A. A. Teploukhov. "Modeling Element Redistribution in the Liquid Phase During Ultrafast Solidification Induced by High-Current Electron Beam Exposure". In 2024 Dynamics of Systems, Mechanisms and Machines (Dynamics), 1–4. IEEE, 2024. https://doi.org/10.1109/dynamics64718.2024.10838695.

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Mlondo, Khanyisani, Mohamed Fayaz Khan e Olanrewaju Lasabi. "Analysis of a Medium Voltage Direct Current Distribution System for Integration of an Electric Vehicle Ultrafast Charging Station: A Case Study". In 2024 IEEE PES/IAS PowerAfrica, 01–05. IEEE, 2024. https://doi.org/10.1109/powerafrica61624.2024.10759361.

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Khurgin, Jacob B. "Optically induced DC current in unbiased dielectrics and semiconductors - a straightforward nonlinear optical effect". In Ultrafast Optics. Washington, D.C.: Optica Publishing Group, 2023. http://dx.doi.org/10.1364/ufo.2023.p1.15.

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We demonstrate theoretically that when well-below-the-bandgap femtosecond optical pulses propagate through a dielectric or semiconductor, DC current and charges are produced even though no real carriers are excited in the bands. This theory is confirmed by recent experiments.

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Feise, M. W., D. S. Citrin, M. Bieler, G. Hein, K. Pierz, U. Siegner e M. Koch. "Spatially resolved current density dynamics in photoconductive switches". In Ultrafast Electronics and Optoelectronics. Washington, D.C.: OSA, 2001. http://dx.doi.org/10.1364/ueo.2001.ufa5.

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Bauer, T., A. B. Hummel, J. S. Kolb, H. G. Roskos, Yu A. Kosevich e K. Köhler. "The Hall Current of Coherent Electron Wavepackets". In International Conference on Ultrafast Phenomena. Washington, D.C.: OSA, 2002. http://dx.doi.org/10.1364/up.2002.tud3.

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Sorokin, Sergey. "Ultrafast Wire Loading with Multi-Megaampere Current". In 2020 7th International Congress on Energy Fluxes and Radiation Effects (EFRE). IEEE, 2020. http://dx.doi.org/10.1109/efre47760.2020.9241993.

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Amano, T., Y. Kawakami, H. Itoh, T. Aoyama, Y. Imai, K. Ohgushi, Y. Nakamura, H. Kishida, K. Yonemitsu e S. Iwai. "Ultrafast magnetization driven by spiral current in Kitaev spin liquid α-RuCl3". In International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 2022. http://dx.doi.org/10.1364/up.2022.tu2a.2.

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In a honeycomb-lattice Mott insulator α-RuCl3, an ultrafast magnetization is induced by circularly polarized excitation of spin-orbit excitons. An ultrafast 6-fs measurement clarifies that the orbital moment emerges from a coherent inter-orbital charge motion.

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Sato, Shunsuke A., Wenwen Mao e Angel Rubio. "THz-induced nonlinear electric current and high-order harmonic generation in graphene". In International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 2022. http://dx.doi.org/10.1364/up.2022.tu4a.9.

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We study the electric transport and high-order harmonic generation in graphene with the quantum master equation. The microscopic mechanism of these THz-induced non-linear phenomena is understood from the viewpoint of the nonequilibrium steady state.

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Manfredi, Giovanni, Paul-Antoine Hervieux e Jerome Hurst. "Ultrafast spin current generation in ferromagnetic thin films". In Spintronics XI, a cura di Henri Jaffrès, Henri-Jean Drouhin, Jean-Eric Wegrowe e Manijeh Razeghi. SPIE, 2018. http://dx.doi.org/10.1117/12.2319953.

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Viotti, Anne-Lise, Marcus Seidel, Gunnar Arisholm, Cord L. Arnold, Chen Guo, Ingmar Hartl, Christoph M. Heyl et al. "Compact multi-pass spectral broadening schemes for XUV pulse generation". In Ultrafast Optics. Washington, D.C.: Optica Publishing Group, 2023. http://dx.doi.org/10.1364/ufo.2023.f3.1.

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This talk addresses the recent developments of the multi-pass cell approach for post-compression to the few-cycle regime. At Lund University and DESY, our current setups employ hybrid multi-pass multi-plates schemes to reach the sub-10 fs regime and drive high repetition rate attosecond XUV pulse generation in a compact manner.

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Rapporti di organizzazioni sul tema "Ultrafast current"

Yang, Xi. Current Status of Developing Ultrafast Mega-electron-volt Electron Microsope. Office of Scientific and Technical Information (OSTI), settembre 2022. http://dx.doi.org/10.2172/1898598.

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