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Nikolay I. Zheludev - One of the best experts on this subject based on the ideXlab platform.
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anapoles and flying Doughnuts
International Conference on Electromagnetics in Advanced Applications, 2019Co-Authors: Nikitas Papasimakis, Apostolos Zdagkas, Vladimir Savinov, Nikolay I. ZheludevAbstract:Toroidal excitations can exist both in matter, as represented by the toroidal multipoles, as well as in free-space in the form of “Flying Doughnuts” [1]. Toroidal multipoles provide significant contributions to the electromagnetic response of matter and together with the conventional electric and magnetic multipoles can lead to non-radiating configurations, termed anapoles. Indeed, anapoles can be formed by a superposition of an electric dipole and a toroidal dipole, which, owing to their identical radiation properties, allow for complete cancellation of radiated electromagnetic fields outside the source. However, although anapoles do not radiate electromagnetic fields, they do act as sources of vector potential (which cannot be eliminated by a change of gauge). On the other hand, Flying Doughnuts are few-cycle electromagnetic pulses with non-trivial spatiotemporal coupling and toroidal configuration of electromagnetic fields that propagate in free-space at the speed of light. They are exact solutions to Maxwell's equations and exhibit strong longitudinal field components along the propagation direction. The spatial and temporal dependence of the Flying Doughnut pulse cannot be separated from one another, which results in a spatially varying frequency spectrum. In particular, the Flying Doughnut pulse exhibits a frequency spectrum that varies across the wavefront with shorter wavelengths localized closer to the center of the pulse and longer wavelengths dominating the outer regions of the pulse. Importantly, this spatial variation remains invariant upon propagation of the pulse, as well as focusing and defocusing, indicating that the Flying Doughnut pulse is isodiffracting. This spatiotemporal coupling in combination with the Doughnut-like arrangement of electromagnetic fields, leads to a complex topological structure in the form of spectrally broadband vortices with multiple singularities in both the electric and magnetic fields. Flying Doughnut pulses can interact with matter in unique ways, which result in non-trivial field transformations upon reflection from perfectly conducting and dielectric interfaces. Moreover, the interactions of Flying Doughnut pulses with spherical dielectric particles can lead to the excitation of toroidal resonances and non-radiating configurations (anapoles).
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Metamaterials for generating space-time coupled few-cycle pulses
2019 Thirteenth International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials), 2019Co-Authors: Apostolos Zdagkas, T. Pu, Vladimir Savinov, Nikitas Papasimakis, H Fang, Nikolay I. ZheludevAbstract:Flying Doughnuts are exact propagating solutions of Maxwell equations in the form of single-cycle, space-time non-separable pulses with complex topology of spectrally broadband vortices. We present the experimental generation of Flying Doughnut pulses and discuss their topological and spatiotemporal structure.
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pulse generation scheme for flying electromagnetic Doughnuts
Physical Review B, 2018Co-Authors: Nikitas Papasimakis, V A Fedotov, T.a. Raybould, Ian J. Youngs, Din Ping Tsai, Nikolay I. ZheludevAbstract:Transverse electromagnetic plane waves are fundamental solutions of Maxwells equations. It is less known that a radically different type of solutions has been described theoretically, but has never been realized experimentally, that exist only in the form of short burst of electromagnetic energy propagating in free-space at the speed of light. They are distinguished from transverse waves by a Doughnut-like configuration of electric and magnetic fields with a strong field component along the propagation direction. Here, we demonstrate numerically that such Flying Doughnuts can be generated from conventional pulses using a singular metamaterial converter designed to manipulate both the spatial and spectral structure of the input pulse. The ability to generate Flying Doughnuts is of fundamental interest, as they shall interact with matter in unique ways, including non-trivial field transformations upon reflection from interfaces and the excitation of toroidal response and anapole modes in matter, thus offering new opportunities for telecommunications, sensing, and spectroscopy.
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generation of electromagnetic Doughnuts
European Quantum Electronics Conference, 2017Co-Authors: Nikitas Papasimakis, Parikshit Moitra, V A Fedotov, T.a. Raybould, Ian J. Youngs, Nikolay I. ZheludevAbstract:We propose from the first time a practical way of generating flying electromagnetic Doughnuts, ultra-short electromagnetic pulses that are exact solutions to Maxwell's equations, distinguished by a Doughnut-like configuration of electric and magnetic fields, strong longitudinal field components along the propagation direction, and unique spatiotemporal coupling [1, 2]. Flying Doughnuts (FDs) are single-cycle, wide bandwidth pulses that propagate in free-space at the speed of light. In contrast to conventional families of pulses, the spatial and temporal dependence of the FD pulse cannot be separated. FD pulses interact with matter in unique ways, including non-trivial field transformations upon reflection from interfaces and the excitation of strong toroidal response in dielectric particles [3].
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Focused electromagnetic Doughnut pulses and their interaction with interfaces and nanostructures.
Optics Express, 2016Co-Authors: T.a. Raybould, Vassili A. Fedotov, Nikitas Papasimakis, Ian J. Youngs, Nikolay I. ZheludevAbstract:“The “focused Doughnut”, a single-cycle electromagnetic perturbation of toroidal topology with inseparable time and spatial dependencies propagates at the speed of light in vacuum, as was shown by Hellwarth and Nouchi in 1996. While normal incidence reflection and refraction of conventional electromagnetic pulses in isotropic media do not lead to polarization changes, “focused Doughnut” pulses undergo complex field transformations owing to the toroidal field structure and the presence of longitudinal components. We also demonstrate that “focused Doughnuts” can interact strongly with structured media exciting dominant dynamic toroidal dipoles in spherical dielectric particles.”
Djenan Ganic - One of the best experts on this subject based on the ideXlab platform.
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Focusing of Doughnut laser beams by a high numerical-aperture objective in free space
Optics Express, 2003Co-Authors: Djenan Ganic, Xiaosong Gan, Min GuAbstract:We report on, in this letter, a phenomenon that the central zerointensity point of a Doughnut beam, caused by phase singularity, disappears in the focus, when such a beam is focused by a high numerical-aperture objective in free space. In addition, the focal shape of the Doughnut beam of a given topological charge exhibits the increased ring intensity in the direction orthogonal to the incident polarization state and an elongation in the polarization direction. These phenomena are caused by the effect of depolarization, associated with a high numerical-aperture objective, and become pronounced by the use of a central obstruction in the objective aperture.
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generation of Doughnut laser beams by use of a liquid crystal cell with a conversion efficiency near 100
Optics Letters, 2002Co-Authors: Djenan Ganic, Xiaosong Gan, Mathias Hain, Somakanthan Somalingam, Svetomir Stankovic, Theo TschudiAbstract:We present a novel technique for producing a Doughnut laser beam by use of a liquid-crystal cell. It is demonstrated that the liquid-crystal cell exhibits an efficiency in energy conversion near 100%. One of the main advantages of this method is its capability of dynamic switching between a Gaussian mode and a Doughnut mode of different topological charges. The liquid-crystal cell is also dynamically tunable over the visible and near-infrared wavelength range. These advantages make the device appealing for laser trapping methods used in single-molecule biomechanics and for optical guiding of cold atoms.
Geoffrey W Stevens - One of the best experts on this subject based on the ideXlab platform.
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prediction of holdup and drop size distribution in a disc Doughnut pulsed column with tenova kinetics internals for the water alamine 336 system
Hydrometallurgy, 2018Co-Authors: Yong Wang, Kathryn A Mumford, Kathryn H Smith, Geoffrey W StevensAbstract:Abstract Tenova Pulsed Column Kinetics Internals (TPC-KIs) are a newly designed type of pulsed column internals with a novel structure that is expected to achieve less back-mixing, higher holdup and improved mass transfer. This study compared the hydrodynamic performance of TPC-KIs with standard disc and Doughnut internals in a 2 m high, 76 mm diameter pulsed solvent extraction column with the water-Alamine 336-Shellsol 2046 system. The effects of the wettability of column internals have also been considered. Dispersed phase holdup and Sauter mean droplet diameter were measured under various pulsation intensities and velocities of both phases, and empirical correlations for holdup and drop size have been refitted within absolute average relative errors of 15%. Tenova kinetics internals have a lower holdup and larger Sauter-mean drop size compared to standard disc and Doughnut internals, and these hydrodynamic parameters are predictable using the correlation developed in this study.
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effect of plate wettability on dispersed phase holdup in a pulsed disc and Doughnut solvent extraction column
Solvent Extraction and Ion Exchange, 2017Co-Authors: Teobaldo Grabin, Kathryn H Smith, Kathryn A Mumford, Yong Wang, Geoffrey W StevensAbstract:ABSTRACTThe effect of plate wettability on the dispersed-phase holdup in a pulsed disc-and-Doughnut solvent extraction column is presented. Teflon, nylon, and stainless steel plates have been used ...
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axial dispersion in a pulsed and nonpulsed disc and Doughnut solvent extraction column
Industrial & Engineering Chemistry Research, 2017Co-Authors: Yong Wang, Kathryn A Mumford, Kathryn H Smith, Geoffrey W StevensAbstract:In solvent extraction columns mechanical agitation is usually introduced to improve the extraction efficiency. However, some industrial columns have been found to have higher extraction efficiency while running with no pulsation. In this study, axial dispersion coefficients in the continuous phase were measured under pulsing and nonpulsing conditions using a 72.5 mm diameter disc and Doughnut solvent extraction column. The axial dispersion coefficients were measured using the unsteady tracer injection method. Under nonpulsing conditions, the axial dispersion coefficient increased with increasing continuous phase velocity, but it did not change significantly with the increase of the dispersed phase velocity. With increasing pulsation intensity, the axial dispersion coefficient increased. A correlation is proposed to predict the continuous phase axial dispersion coefficient in a pulsing and nonpulsing disc and Doughnut solvent extraction column.
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pulsed disc and Doughnut column performance
Solvent Extraction and Ion Exchange, 2009Co-Authors: Ali B Jahya, Geoffrey W Stevens, H R C PrattAbstract:Abstract: A study of the hydrodynamic variables, drop size, continuous phase axial dispersion, and mass‐transfer coefficients of a pulsed annular disc‐and‐Doughnut liquid extraction column are presented for three different systems. The results indicate that the characteristic velocity plot of Gayler et al. (1953) can be used to describe the variation of holdup with flow rate for a range of pulsation velocities. The existence of several different operating regimes, namely streamline, mixer‐settler, and emulsion regimes, was observed when the input energy was altered. Mass‐transfer data from 72.5 mm i.d. and 2.5 m i.d. columns were interpreted in terms of the differential axial‐dispersion model; the number of transfer units in a unit length of column is proposed as the basis for scale‐up of the mass‐transfer performance. By considering the free areas in the column, a method is proposed for the geometric scale‐up of pulsed disc‐and‐Doughnut columns.
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comparison of the performance of a pulsed disc and Doughnut column with a pulsed sieve plate liquid extraction column
Solvent Extraction and Ion Exchange, 2005Co-Authors: Ali B Jahya, H Clive R Pratt, Geoffrey W StevensAbstract:Abstract The hydrodynamic and mass‐transfer performance of a 75 mm diameter pulsed disc and Doughnut column (PDD) and a pulsed sieve‐plate column (PSP) are presented and compared for a toluene–acetone–water system under similar operating conditions. It was found that the pulsed disc and Doughnut column flooded earlier than the pulsed sieve‐plate column, indicating that the total throughput per unit cross‐sectional area through the pulsed disc and Doughnut column was less. At similar operating conditions (i.e., flowrates, pulse frequency, and amplitude), the mass‐transfer performance of the pulsed disc and Doughnut column was higher, and its holdup higher. The mass‐transfer performance of the PSP column, when compared at similar holdup to the PDD, was found to be higher, and so it is concluded that it is a more efficient column for this system.
Min Gu - One of the best experts on this subject based on the ideXlab platform.
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Focusing of Doughnut laser beams by a high numerical-aperture objective in free space
Optics Express, 2003Co-Authors: Djenan Ganic, Xiaosong Gan, Min GuAbstract:We report on, in this letter, a phenomenon that the central zerointensity point of a Doughnut beam, caused by phase singularity, disappears in the focus, when such a beam is focused by a high numerical-aperture objective in free space. In addition, the focal shape of the Doughnut beam of a given topological charge exhibits the increased ring intensity in the direction orthogonal to the incident polarization state and an elongation in the polarization direction. These phenomena are caused by the effect of depolarization, associated with a high numerical-aperture objective, and become pronounced by the use of a central obstruction in the objective aperture.
T.a. Raybould - One of the best experts on this subject based on the ideXlab platform.
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pulse generation scheme for flying electromagnetic Doughnuts
Physical Review B, 2018Co-Authors: Nikitas Papasimakis, V A Fedotov, T.a. Raybould, Ian J. Youngs, Din Ping Tsai, Nikolay I. ZheludevAbstract:Transverse electromagnetic plane waves are fundamental solutions of Maxwells equations. It is less known that a radically different type of solutions has been described theoretically, but has never been realized experimentally, that exist only in the form of short burst of electromagnetic energy propagating in free-space at the speed of light. They are distinguished from transverse waves by a Doughnut-like configuration of electric and magnetic fields with a strong field component along the propagation direction. Here, we demonstrate numerically that such Flying Doughnuts can be generated from conventional pulses using a singular metamaterial converter designed to manipulate both the spatial and spectral structure of the input pulse. The ability to generate Flying Doughnuts is of fundamental interest, as they shall interact with matter in unique ways, including non-trivial field transformations upon reflection from interfaces and the excitation of toroidal response and anapole modes in matter, thus offering new opportunities for telecommunications, sensing, and spectroscopy.
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generation of electromagnetic Doughnuts
European Quantum Electronics Conference, 2017Co-Authors: Nikitas Papasimakis, Parikshit Moitra, V A Fedotov, T.a. Raybould, Ian J. Youngs, Nikolay I. ZheludevAbstract:We propose from the first time a practical way of generating flying electromagnetic Doughnuts, ultra-short electromagnetic pulses that are exact solutions to Maxwell's equations, distinguished by a Doughnut-like configuration of electric and magnetic fields, strong longitudinal field components along the propagation direction, and unique spatiotemporal coupling [1, 2]. Flying Doughnuts (FDs) are single-cycle, wide bandwidth pulses that propagate in free-space at the speed of light. In contrast to conventional families of pulses, the spatial and temporal dependence of the FD pulse cannot be separated. FD pulses interact with matter in unique ways, including non-trivial field transformations upon reflection from interfaces and the excitation of strong toroidal response in dielectric particles [3].
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Focused electromagnetic Doughnut pulses and their interaction with interfaces and nanostructures.
Optics Express, 2016Co-Authors: T.a. Raybould, Vassili A. Fedotov, Nikitas Papasimakis, Ian J. Youngs, Nikolay I. ZheludevAbstract:“The “focused Doughnut”, a single-cycle electromagnetic perturbation of toroidal topology with inseparable time and spatial dependencies propagates at the speed of light in vacuum, as was shown by Hellwarth and Nouchi in 1996. While normal incidence reflection and refraction of conventional electromagnetic pulses in isotropic media do not lead to polarization changes, “focused Doughnut” pulses undergo complex field transformations owing to the toroidal field structure and the presence of longitudinal components. We also demonstrate that “focused Doughnuts” can interact strongly with structured media exciting dominant dynamic toroidal dipoles in spherical dielectric particles.”
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Focused electromagnetic Doughnut pulses and their interaction with interfaces and nanostructures
Optics express, 2016Co-Authors: T.a. Raybould, Vassili A. Fedotov, Nikitas Papasimakis, Ian J. Youngs, Nikolay I. ZheludevAbstract:We study the propagation properties and light-matter interactions of the focused Doughnut pulses, broadband, single-cycle electromagnetic perturbations of toroidal topology first described by Hellwarth and Nouchi in 1996. We show how focused Doughnuts are reflected and refracted at planar metallic and vacuum-dielectric interfaces leading to complex distortions of the field structure. We also identify the conditions under which these toroidal pulses excite dominant dynamic toroidal dipoles in spherical dielectric particles.