Search results for "RADIATION"
showing 10 items of 5298 documents
Efficient metallic spintronic emitters of ultrabroadband terahertz radiation
2016
Terahertz electromagnetic radiation is extremely useful for numerous applications such as imaging and spectroscopy. Therefore, it is highly desirable to have an efficient table-top emitter covering the 1-to-30-THz window whilst being driven by a low-cost, low-power femtosecond laser oscillator. So far, all solid-state emitters solely exploit physics related to the electron charge and deliver emission spectra with substantial gaps. Here, we take advantage of the electron spin to realize a conceptually new terahertz source which relies on tailored fundamental spintronic and photonic phenomena in magnetic metal multilayers: ultrafast photo-induced spin currents, the inverse spin-Hall effect an…
Synthesis of Nonplanar Graphene Nanoribbon with Fjord Edges
2021
As a new family of semiconductors, graphene nanoribbons (GNRs), nanometer-wide strips of graphene, have appeared as promising candidates for next-generation nanoelectronics. Out-of-plane deformation of π-frames in GNRs brings further opportunities for optical and electronic property tuning. Here we demonstrate a novel fjord-edged GNR (FGNR) with a nonplanar geometry obtained by regioselective cyclodehydrogenation. Triphenanthro-fused teropyrene 1 and pentaphenanthro-fused quateropyrene 2 were synthesized as model compounds, and single-crystal X-ray analysis revealed their helically twisted conformations arising from the [5]helicene substructures. The structures and photophysical properties …
Ultrafast amplification and non-linear magneto-elastic coupling of coherent magnon modes in an antiferromagnet
2021
We investigate the role of domain walls in the ultrafast magnon dynamics of an antiferromagnetic NiO single crystal in a pump-probe experiment with variable pump photon energy. Analysing the amplitude of the energy-dependent photo-induced ultrafast spin dynamics, we detect a yet unreported coupling between the material's characteristic THz- and a GHz-magnon modes. We explain this unexpected coupling between two orthogonal eigenstates of the corresponding Hamiltonian by modelling the magneto-elastic interaction between spins in different domains. We find that such interaction, in the non-linear regime, couples the two different magnon modes via the domain walls and it can be optically exploi…
Dynamical amplification of electric polarization through nonlinear phononics in 2D SnTe
2020
Ultrafast optical control of ferroelectricity using intense terahertz fields has attracted significant interest. Here we show that the nonlinear interactions between two optical phonons in SnTe, a two-dimensional in-plane ferroelectric material, enables a dynamical amplification of the electric polarization within subpicoseconds time domain. Our first-principles time-dependent simulations show that the infrared-active out-of-plane phonon mode, pumped to nonlinear regimes, spontaneously generates in-plane motions, leading to rectified oscillations in the in-plane electric polarization. We suggest that this dynamical control of ferroelectric material, by nonlinear phonon excitation, can be ut…
Terahertz electrical writing speed in an antiferromagnetic memory
2018
The speed of writing of state-of-the-art ferromagnetic memories is physically limited by an intrinsic gigahertz threshold. Recently, realization of memory devices based on antiferromagnets, in which spin directions periodically alternate from one atomic lattice site to the next has moved research in an alternative direction. We experimentally demonstrate at room temperature that the speed of reversible electrical writing in a memory device can be scaled up to terahertz using an antiferromagnet. A current-induced spin-torque mechanism is responsible for the switching in our memory devices throughout the 12-order-of-magnitude range of writing speeds from hertz to terahertz. Our work opens the…
Real time monitoring of water level and temperature in storage fuel pools through optical fibre sensors
2017
AbstractWe present an innovative architecture of a Rayleigh-based optical fibre sensor for the monitoring of water level and temperature inside storage nuclear fuel pools. This sensor, able to withstand the harsh constraints encountered under accidental conditions such as those pointed-out during the Fukushima-Daiichi event (temperature up to 100 °C and radiation dose level up to ~20 kGy), exploits the Optical Frequency Domain Reflectometry technique to remotely monitor a radiation resistant silica-based optical fibre i.e. its sensing probe. We validate the efficiency and the robustness of water level measurements, which are extrapolated from the temperature profile along the fibre length, …
Transition metal ions luminescence in neutron irradiated magnesium oxide
2010
The results of investigation of the photoluminescence (PL), its excitation and optical absorption of MgO crystals doped with different concentrations of transition metals exposed to fast neutron irradiation and after annealing are presented. It is suggested that the 440 nm photoluminescence band belongs to the complex V−OH-Fe3+ center with tetragonal symmetry, the ~730 nm PL band observed in the irradiated MgO crystals is connected with defects, generated as a result of decay of the complex V−OH-Fe3+ centers. The near infrared luminescence bands in MgO crystals are connected with Fe3+-Fe3+ exchange coupled pairs.
Integrazione di celle fotovoltaiche ibride nel vetromattone
2012
L’invenzione riguarda l’integrazione del vetromattone con celle solari ibride (organiche/inorganiche), conosciute come Dye-sensitized Solar Cell (DSC). La combinazione del vetromattone con le DSC consente di migliorare le prestazioni del prodotto originario rendendolo in grado di produrre energia pulita. Le caratteristiche di trasparenza e isolamento termo-acustico del prodotto possono essere regolate agendo sulla configurazione delle DSC. Il prodotto può essere assemblato a formare pannelli fotovoltaici per la realizzazione di facciate traslucide energeticamente “attive” in varie condizioni luminose (condizioni di luce diffusa o artificiale) e indipendentemente dall’angolo di radiazione so…
Interventistica eco-guidata per l’articolazione d’anca
2013
Lo scopo di questo lavoro è di rivedere le principali applicazioni della interventistica eco-guidata d’anca, descrivendone le indicazioni e la metodologia. L’ecografia è una metodica considerata sicura per i pazienti, in quanto non è stato dimostrato un possibile danno dovuto all’energia trasmessa dagli ultrasuoni ai tessuti del paziente, contrariamente alle metodiche che fanno uso di radiazioni ionizzanti, come la radiografia convenzionale e la tomografia computerizzata. Inoltre, l’ecografia risulta rapida ed efficace nel guidare l’ago verso la sede voluta evitando di intercettare strutture vascolari e/o nervose, consentendo quindi una maggiore sicurezza, rispetto alle tecniche interventis…
Transition probabilities for some infrared O I spectral lines—Application for determining excitation temperatures in low temperature plasmas
2008
Intensities of selected spectral transitions of neutral oxygen emitted from a wall-stabilized arc have been measured. Applying reliable transition probability data taken from literature, Boltzmann plots have been constructed and the temperatures of the plasma have been obtained. At arc plasma conditions ensuring partial local thermal equilibrium, transition probabilities for 4 O I spectral lines from the near infrared spectral range have been obtained. These new results, together with data for two other studied O I spectral lines taken from the National Institute of Standards and Technology data base, are proposed as a suitable set of transition probabilities applicable for diagnostics of l…