| 1. |
- Lomholt, Michael A., et al.
(författare)
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Microscopic Origin of the Logarithmic Time Evolution of Aging Processes in Complex Systems
- 2013
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Ingår i: Physical Review Letters. - : American Physical Society. - 1079-7114 .- 0031-9007. ; 110:20
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Tidskriftsartikel (refereegranskat)abstract
- There exists compelling experimental evidence in numerous systems for logarithmically slow time evolution, yet its full theoretical understanding remains elusive. We here introduce and study a generic transition process in complex systems, based on nonrenewal, aging waiting times. Each state n of the system follows a local clock initiated at t = 0. The random time tau between clock ticks follows the waiting time density psi (tau). Transitions between states occur only at local clock ticks and are hence triggered by the local forward waiting time, rather than by psi (tau). For power-law forms psi (tau) similar or equal to tau(-1-alpha) (0 < alpha < 1) we obtain a logarithmic time evolution of the state number < n(t)> similar or equal to log(t/t(0)), while for alpha > 2 the process becomes normal in the sense that < n(t)> similar or equal to t. In the intermediate range 1 < alpha < 2 we find the power-law growth < n(t)> similar or equal to t(alpha-1). Our model provides a universal description for transition dynamics between aging and nonaging states.
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| 2. |
- Maccaferri, Nicolò, et al.
(författare)
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Effects of a non-absorbing substrate on the magneto-optical Kerr response of plasmonic ferromagnetic nanodisks
- 2014
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 211:5, s. 1067-1075
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Tidskriftsartikel (refereegranskat)abstract
- Magnetoplasmonics is an emerging field of intense research on materials combining magnetic and plasmonic functionalities. The novel optical and magneto-optical (MO) properties displayed by these materials could allow the design of a new class of magnetically controllable optical nano-devices. In this work, we investigate the effects of a non-absorbing (insulating) substrate on the MO activity of pure ferromagnetic disk-shaped nanostructures supporting localized plasmon resonances. We show that the red-shift of the localized plasmon resonance, related to the modification of the localization of the electromagnetic field due to the substrate, is not the only effect that the substrate has on the MO response. We demonstrate that the reflectivity of the substrate itself plays a key role in determining the MO response of the system. We discuss why it is so and provide a description of the modeling tools suitable to take into account both effects. Understanding the role of the substrate will permit a more aware design of magnetoplasmonic nanostructured devices for future biotechnological and optoelectronic applications. [GRAPHICS] Ferromagnetic nickel nanodisk in vacuum (left) and on a non-absorbing substrate (right), illuminated by linearly polarized light. The polarization of the reflected field is changed in the first case due to a combination of intrinsic magneto-optical properties and the nanoconfinement of the material. In the second case, the polarization of the reflected light is affected also by the presence of the substrate.
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| 3. |
- Wallstén Wallin, Erik Karl, 1986, et al.
(författare)
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Three-wave interaction and Manley-Rowe relations in quantum hydrodynamics
- 2014
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Ingår i: Journal of Plasma Physics. - : Cambridge University Press. - 0022-3778 .- 1469-7807. ; 80, s. 643-
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Tidskriftsartikel (refereegranskat)abstract
- The theory for nonlinear three-wave interaction in magnetized plasmas is reconsidered using quantum hydrodynamics. The general coupling coefficients are calculated for the generalized Bohm de Broglie term. It is found that the Manley–Rowe relations are fulfilled only if the form of the particle dispersive term coincides with the standard expression. The implications of our results are discussed.
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| 4. |
- Gonoskov, Arkady, 1984, et al.
(författare)
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Employing machine learning for theory validation and identification of experimental conditions in laser-plasma physics
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- The validation of a theory is commonly based on appealing to clearly distinguishable and describable features in properly reduced experimental data, while the use of ab-initio simulation for interpreting experimental data typically requires complete knowledge about initial conditions and parameters. We here apply the methodology of using machine learning for overcoming these natural limitations. We outline some basic universal ideas and show how we can use them to resolve long-standing theoretical and experimental difficulties in the problem of high-intensity laser-plasma interactions. In particular we show how an artificial neural network can “read” features imprinted in laser-plasma harmonic spectra that are currently analysed with spectral interferometry.
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| 5. |
- Horny, Vojtech, 1989, et al.
(författare)
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Generation of single attosecond relativistic electron bunch from intense laser interaction with a nanosphere
- 2021
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 63:12
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Tidskriftsartikel (refereegranskat)abstract
- Ultrahigh-intensity laser-plasma physics provides unique light and particle beams as well as novel physical phenomena. A recently available regime is based on the interaction between a relativistic intensity few-cycle laser pulse and a sub-wavelength-sized mass-limited plasma target. Here, we investigate the generation of electron bunches under these extreme conditions by means of particle-in-cell simulations. In a first step, up to all electrons are expelled from the nanodroplet and gain relativistic energy from time-dependent local field enhancement at the surface. After this ejection, the electrons are further accelerated as they copropagate with the laser pulse. As a result, a few, or under specific conditions isolated, pC-class relativistic attosecond electron bunches are generated with laser pulse parameters feasible at state-of-the-art laser facilities. This is particularly interesting for some applications, such as generation of attosecond x-ray pulses via Thomson backscattering.
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| 6. |
- Jenab, Mehdi, 1982, et al.
(författare)
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Ultrafast electron holes in plasma phase space dynamics
- 2021
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Electron holes (EH) are localized modes in plasma kinetic theory which appear as vortices in phase space. Earlier research on EH is based on the Schamel distribution function (df). A novel df is proposed here, generalizing the original Schamel df in a recursive manner. Nonlinear solutions obtained by kinetic simulations are presented, with velocities twice the electron thermal speed. Using 1D-1V kinetic simulations, their propagation characteristics are traced and their stability is established by studying their long-time evolution and their behavior through mutual collisions.
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| 7. |
- Hassan, Emadeldeen, et al.
(författare)
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Anapole metallic nanostructures for metarsurface applications
- 2023
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Ingår i: META 2023 Paris - France. The 13th International Conference on Metamaterials, Photonic Crystals and Plasmonics. - : META Conference. ; , s. 583-583
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Konferensbidrag (refereegranskat)abstract
- Anapole states are broadly investigated in nanophotonics for their ability to provide field enhancement and transparency. While low extinction has been achieved in dielectric nanoparticles due to the absence of intrinsic losses, in the case of plasmonic nanostructures this is still elusive. In this talk, we will present recent findings on anapole states in planar plasmonic nanostructures that were optimized for near-fieldenergy enhancement using a topology optimization approach. The optimized structures exhibit an anapole state with characteristic properties in the visible regime including weak absorption, high near-field enhancement outside the structure, and strong suppression of scattering. We use our multipole analysis to explain both thenear-field and the far-field features of the anapole state possessed by the nanostructures. Because of the low inter-coupling at the anapole state, the nanostructures act as individual meta-atoms that preserve their optical response even when used in highly packed metasurfaces and metamaterials. Due to their transparency while providing field enhancement, anapoles might be combined with waveguides in integrated optical platforms to unlock advanced functionalities for sensing, nonlinear optics, and optical information processing.
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| 8. |
- Sarmad, Shokat, et al.
(författare)
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Amine functionalized deep eutectic solvent for CO2 capture : Measurements and modeling
- 2020
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Ingår i: Journal of Molecular Liquids. - : Elsevier. - 0167-7322 .- 1873-3166. ; 309
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Tidskriftsartikel (refereegranskat)abstract
- Deep eutectic solvents (DESs) have gained a great interest among researchers owing to their inherent advantages to become an adaptable alternative to ionic liquids (ILs) and common amine solutions for CO2 capture. In the present study, we prepared five new three-component DESs by functionalization of choline chloride-ethanolamine (1,7, mol,mol) DES using different types of amines: diethanolamine (amine type 2), methyldiethanolamine (amine type 3), piperazine (amine type 2) as well as 1-(2-aminoethyl)piperazine (amine type 1 and 2). All of the prepared DESs are liquid at room temperature and their melting points were in the range of 265–276 K. The solubility of CO2 in the studied DESs was measured at pressures up to 2 MPa and 298.15 K. The obtained experimental data were analyzed by the use of generic Redlich-Kwong equation of state (RK-EOS) model and Henry's law constant have been calculated from the obtained experimental data through the EOS correlation. All the studied DESs show chemical absorption of CO2 which can be approved based on the excess enthalpy and Gibbs energy functions. FT-IR spectroscopy and 13C NMR verified the formation of carbamate in the CO2 absorption process which revealed the chemisorption of CO2 in the studied DESs. The ideal association model has been utilized to describe the excess thermodynamic functions and two different types of the chemical association have been detected AB2 and AB, (A refer to DESs and B to CO2). Based on the obtained solubility data, the amines that enhanced the absorption capacity of choline chloride-ethanolamine (1,7) follow the trend as follows: piperazine > aminoethylpiperazine > methyldiethanolamine > diethanolamine. Therefore, piperazine can be considered as an absorption enhancer. The viscosity of DESs before and after CO2 absorption as well as the thermal behavior of the DESs were also investigated.
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| 9. |
- Segervald, Jonas, et al.
(författare)
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Plasmonic metasurface assisted by thermally imprinted polymer nano‐well array for surface enhanced Raman scattering
- 2022
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Ingår i: Nano Select. - : John Wiley & Sons. - 2688-4011. ; 3:9, s. 1344-1353
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Tidskriftsartikel (refereegranskat)abstract
- Plasmonic nanometasurfaces/nanostructures possess strong electromagnetic field enhancement caused by resonant oscillations of free electrons, and has been extensively applied in biosensing, nanophotonic and photocatalysis. However, fabrication of uniform nanostructured metasurfaces by conventional methods is complicated and costly, which mitigates a wide-spread use of this technique in ubiquitous applications. Here, we present a facile and scalable method to fabricate an active nanotrench plasmonic gold substrate. The surface comprises sub-10 nm plasmonic nanogaps and their formation is assisted by a pre-fabrication of nano-imprinted polymer nano-well arrays. The plasmonic metasurface is optimized to maximize the density of the nano-trenches by tuning the substrate material, imprinting procedure and film deposition. We show that the surface Raman enhancement due to plasmonic resonances correlates well with trench density and reach a meritorious enhancement factor of EF > 105 over large surfaces.We further show that the electric field strength at the nanotrench features are well explained by finite element method simulations using COMSOL Multiphysics. The plasmonic substrate is transparent in the visible spectrum and conductive. In combination with a scalable bottom-up fabrication the plasmonic metasurface opens up for a wider use of the sensitive and reliable SERS substrate in applications such as portable sensing devices and for future internet of things.
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| 10. |
- Björklund Svensson, Jonas, et al.
(författare)
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Low-divergence femtosecond X-ray pulses from a passive plasma lens
- 2021
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Ingår i: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2481 .- 1745-2473. ; 17:5, s. 639-645
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Tidskriftsartikel (refereegranskat)abstract
- Electron and X-ray beams originating from compact laser-wakefield accelerators have very small source sizes that are typically on the micrometre scale. Therefore, the beam divergences are relatively high, which makes it difficult to preserve their high quality during transport to applications. To improve on this, tremendous efforts have been invested in controlling the divergence of the electron beams, but no mechanism for generating collimated X-ray beams has yet been demonstrated experimentally. Here we propose and realize a scheme where electron bunches undergoing focusing in a dense, passive plasma lens can emit X-ray pulses with divergences approaching the incoherent limit. Compared with conventional betatron emission, the divergence of this so-called plasma lens radiation is reduced by more than an order of magnitude in solid angle, while maintaining a similar number of emitted photons per electron. This X-ray source offers the possibility of producing brilliant and collimated few-femtosecond X-ray pulses for ultra-fast science, in particular for studies based on X-ray diffraction and absorption spectroscopy. X-ray pulses with low divergences are produced in a laser-wakefield accelerator by focusing electron bunches in a dense passive plasma lens.
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