The Experts below are selected from a list of 26127 Experts worldwide ranked by ideXlab platform
Kishan Dholakia - One of the best experts on this subject based on the ideXlab platform.
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Optical manipulation of a dielectric particle along polygonal closed-loop geometries within a single water droplet
'Springer Science and Business Media LLC', 2021Co-Authors: Junbum Park, Seongjin Hong, Yong Soo Lee, Hyeonwoo Lee, Seokjin Kim, Kishan DholakiaAbstract:Abstract We report a new method to optically manipulate a single dielectric particle along closed-loop polygonal trajectories by crossing a suite of all-fiber Bessel-like beams within a single water droplet. Exploiting optical radiation pressure, this method demonstrates the circulation of a single polystyrene bead in both a triangular and a rectangle geometry enabling the Trapped particle to undergo multiple circulations successfully. The crossing of the Bessel-like beams creates polygonal corners where the Trapped Particles successfully make abrupt turns with acute angles, which is a novel capability in microfluidics. This offers an optofluidic paradigm for particle transport overcoming turbulences in conventional microfluidic chips
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generation of multiple bessel beams for a biophotonics workstation
Optics Express, 2008Co-Authors: Tomas Cizmar, Věra Kollarova, X Tsampoula, Frank J Gunnmoore, W Sibbett, Zdeněk Bouchal, Kishan DholakiaAbstract:We present a simple method using an axicon and spatial light modulator to create multiple parallel Bessel beams and precisely control their individual positions in three dimensions. This technique is tested as an alternative to classical holographic beam shaping commonly used now in optical tweezers. Various applications of precise control of multiple Bessel beams are demonstrated within a single microscope giving rise to new methods for three-dimensional positional control of Trapped Particles or active sorting of micro-objects as well as “focus-free” photoporation of living cells. Overall this concept is termed a ‘biophotonics workstation’ where users may readily trap, sort and porate material using Bessel light modes in a microscope.
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optical sorting and detection of submicrometer objects in a motional standing wave
Physical Review B, 2006Co-Authors: Tomas Cizmar, V Garceschavez, Martin Siler, Mojmir Serý, Pavel Zemanek, Kishan DholakiaAbstract:An extended interference pattern close to the surface may result in either a transmissive or an evanescent surface field for large-area manipulation of Trapped Particles. The affinity of differing particle sizes to a moving standing-wave light pattern allows us to hold and deliver them in a bidirectional manner and demonstrate experimentally particle sorting in the submicrometer region. This is performed without the need of fluid flow (static sorting). Theoretical predictions support the experimental observations that certain sizes of colloidal Particles thermally hop more easily between neighboring traps. A generic method is also presented for particle position detection in an extended periodic light pattern and applied to characterization of optical traps and particle behavior.
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orbital angular momentum transfer in helical mathieu beams
Optics Express, 2006Co-Authors: Carlos Lopezmariscal, Julio C Gutierrezvega, Graham Milne, Kishan DholakiaAbstract:We observe the transfer of orbital angular momentum to Trapped Particles in the azimuthally asymmetric transverse intensity distribution of a helical Mathieu beam. The average rotation rate, instantaneous angular displacement and terminal velocity of the Trapped Particles are measured experimentally. The angular dependence of these parameters is found to be in good agreement with the variation of the optical gradient force, the transfer of OAM from the wavefield and the Stokes drag force.
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the reconstruction of optical angular momentum after distortion in amplitude phase and polarization
Journal of Optics, 2004Co-Authors: V Garceschavez, David Mcgloin, Michael D Summers, Alberto Fernandeznieves, Gabriel C Spalding, Galder Cristobal, Kishan DholakiaAbstract:Propagation through a distorting obstacle may significantly influence the amplitude, phase and polarization state of a light beam. This potentially has consequences for the behaviour of the optical angular momentum of light. We experimentally study how both the spin and orbital angular momentum (OAM) of light behaves upon passage through microscopic optically Trapped Particles. Particles Trapped with Gaussian and, separately, Bessel light beams in two spatially distinct sample chambers are studied with Trapped objects in the first chamber acting as distorting obstacles. The Bessel beam can reconstruct its spatial form and this shows reconstruction of both spin and OAM over extended distances.
C F Driscoll - One of the best experts on this subject based on the ideXlab platform.
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plasma heating due to cyclic diffusion across a separatrix
Physical Review Letters, 2019Co-Authors: Francois Anderegg, D H E Dubin, M. Affolter, C F DriscollAbstract:We observe plasma heating due to collisional diffusion across a separatrix when a magnesium ion column in a Penning-Malmberg trap is cyclically pushed back and forth across a partial trapping barrier. The barrier is an externally applied axisymmetric "squeeze" potential, which creates a velocity separatrix between Trapped and passing Particles. Weak ion-ion collisions then cause separatrix crossings, leading to irreversible heating. The heating rate scales as the square root of the oscillation rate times the collision frequency and thus can be dominant for low-collisionality plasmas. The particle velocity distribution function is measured with coherent laser induced fluorescence and shows passing and Trapped Particles having an out-of-phase response to the forced plasma oscillations.
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Trapped Particle Effects in the Parametric Instability of Near-Acoustic Plasma Waves.
Physical review letters, 2018Co-Authors: M. Affolter, Francois Anderegg, Daniel H. E. Dubin, Francesco Valentini, C F DriscollAbstract:Quantitative experiments on the parametric decay instability of near-acoustic plasma waves provide strong evidence that Trapped Particles reduce the instability threshold below fluid models. At low temperatures, the broad characteristics of the parametric instability are determined by the frequency detuning of the pump and daughter wave, and the wave-wave coupling strength, surprisingly consistent with cold fluid, three-wave theories. However, at higher temperatures, Trapped particle effects dominate, and the pump wave becomes unstable at half the threshold pump wave amplitude with similar exponential growth rates as for a cold plasma.
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damping of the Trapped particle diocotron mode
Physical Review Letters, 2003Co-Authors: T. J. Hilsabeck, A A Kabantsev, C F Driscoll, T M OneilAbstract:The damping mechanism of a recently discovered Trapped-particle mode is identified as collisional velocity scattering of marginally Trapped Particles. The mode exists on non-neutral plasma columns that are partially divided by an electrostatic potential. This damping mechanism is similar to that responsible for damping of the dissipative Trapped-ion mode. The damping rate is calculated using a Fokker-Planck analysis and agrees with measurement to within 50%. Also, an experimental signature confirms a causal relation between scattering of marginally Trapped Particles and damping. Electric and magnetic field inhomogeneities in plasma containment devices cause a fraction of the Particles to remain localized in certain regions. This condition gives rise to a class of low frequency electrostatic oscillations known as Trapped-particle modes [1]. In these modes, Trapped Particles remain isolated from the global mode
N J Fisch - One of the best experts on this subject based on the ideXlab platform.
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adiabatic nonlinear waves with Trapped Particles iii wave dynamics
Physics of Plasmas, 2012Co-Authors: I Y Dodin, N J FischAbstract:The evolution of adiabatic waves with autoresonant Trapped Particles is described within the Lagrangian model developed in Paper I, under the assumption that the action distribution of these Particles is conserved, and, in particular, that their number within each wavelength is a fixed independent parameter of the problem. One-dimensional nonlinear Langmuir waves with deeply Trapped electrons are addressed as a paradigmatic example. For a stationary wave, tunneling into overcritical plasma is explained from the standpoint of the action conservation theorem. For a nonstationary wave, qualitatively different regimes are realized depending on the initial parameter S, which is the ratio of the energy flux carried by Trapped Particles to that carried by passing Particles. At S 1/2, the Trapped-particle modulational instability (TPMI) develops, in contrast with the existing theories of the TPMI yet in agreement with the general sideband insta...
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adiabatic nonlinear waves with Trapped Particles iii wave dynamics
arXiv: Plasma Physics, 2011Co-Authors: I Y Dodin, N J FischAbstract:The evolution of adiabatic waves with autoresonant Trapped Particles is described within the Lagrangian model developed in Paper I, under the assumption that the action distribution of these Particles is conserved, and, in particular, that their number within each wavelength is a fixed independent parameter of the problem. One-dimensional nonlinear Langmuir waves with deeply Trapped electrons are addressed as a paradigmatic example. For a stationary wave, tunneling into overcritical plasma is explained from the standpoint of the action conservation theorem. For a nonstationary wave, qualitatively different regimes are realized depending on the initial parameter $S$, which is the ratio of the energy flux carried by Trapped Particles to that carried by passing Particles. At $S 1/2$, the Trapped-particle modulational instability (TPMI) develops, in contrast with the existing theories of the TPMI yet in agreement with the general sideband instability theory. Remarkably, these effects are not captured by the nonlinear Schr\"odinger equation, which is traditionally considered as a universal model of wave self-action but misses the Trapped-particle oscillation-center inertia.
D H E Dubin - One of the best experts on this subject based on the ideXlab platform.
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plasma heating due to cyclic diffusion across a separatrix
Physical Review Letters, 2019Co-Authors: Francois Anderegg, D H E Dubin, M. Affolter, C F DriscollAbstract:We observe plasma heating due to collisional diffusion across a separatrix when a magnesium ion column in a Penning-Malmberg trap is cyclically pushed back and forth across a partial trapping barrier. The barrier is an externally applied axisymmetric "squeeze" potential, which creates a velocity separatrix between Trapped and passing Particles. Weak ion-ion collisions then cause separatrix crossings, leading to irreversible heating. The heating rate scales as the square root of the oscillation rate times the collision frequency and thus can be dominant for low-collisionality plasmas. The particle velocity distribution function is measured with coherent laser induced fluorescence and shows passing and Trapped Particles having an out-of-phase response to the forced plasma oscillations.
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parametric instability driven by weakly Trapped Particles in nonlinear plasma waves
Physical Review Letters, 2018Co-Authors: D H E DubinAbstract:This Letter describes a new parametric instability mechanism caused by a distribution f_{T} of Particles Trapped in the potential wells of a wave train. The mechanism explains a nonlinear instability in Trivelpiece-Gould (TG) waves, and it could also be a destabilizing factor in a range of nearly collisionless nonlinear plasma waves. The theory is compared to particle in cell simulations of TG waves.
T. Fischer - One of the best experts on this subject based on the ideXlab platform.
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the isotropic diffusion source approximation for supernova neutrino transport
The Astrophysical Journal, 2009Co-Authors: Mathias Liebendorfer, S C Whitehouse, T. FischerAbstract:Astrophysical observations originate from matter that interacts with radiation or transported Particles. We develop a pragmatic approximation in order to enable multidimensional simulations with basic spectral radiative transfer when the available computational resources are not sufficient to solve the complete Boltzmann transport equation. The distribution function of the transported Particles is decomposed into a Trapped particle component and a streaming particle component. Their separate evolution equations are coupled by a source term that converts Trapped Particles into streaming Particles. We determine this source term by requiring the correct diffusion limit for the evolution of the Trapped particle component. For a smooth transition to the free streaming regime, this "diffusion source" is limited by the matter emissivity. The resulting streaming particle emission rates are integrated over space to obtain the streaming particle flux. Finally, a geometric estimate of the flux factor is used to convert the particle flux to the streaming particle density, which enters the evaluation of streaming particle-matter interactions. The efficiency of the scheme results from the freedom to use different approximations for each particle component. In supernovae, for example, reactions with Trapped Particles on fast timescales establish equilibria that reduce the number of primitive variables required to evolve the Trapped particle component. On the other hand, a stationary-state approximation considerably facilitates the treatment of the streaming particle component. Different approximations may apply in applications to stellar atmospheres, star formation, or cosmological radiative transfer. We compare the isotropic diffusion source approximation with Boltzmann neutrino transport of electron flavor neutrinos in spherically symmetric supernova models and find good agreement. An extension of the scheme to the multidimensional case is also discussed.
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the isotropic diffusion source approximation for supernova neutrino transport
arXiv: Astrophysics, 2007Co-Authors: M Liebendoerfer, S C Whitehouse, T. FischerAbstract:Astrophysical observations originate from matter that interacts with radiation or transported Particles. We develop a pragmatic approximation in order to enable multi-dimensional simulations with basic spectral radiative transfer when the computational resources are not sufficient to solve the complete Boltzmann transport equation. The distribution function of the transported Particles is decomposed into Trapped and streaming particle components. Their separate evolution equations are coupled by a source term that converts Trapped Particles into streaming Particles. We determine this source term by requiring the correct diffusion limit. For a smooth transition to the free streaming regime, this 'diffusion source' is limited by the matter emissivity. The resulting streaming particle emission rates are integrated over space to obtain the streaming particle flux. A geometric estimate of the flux factor is used to convert the particle flux to the streaming particle density. The efficiency of the scheme results from the freedom to use different approximations for each particle component. In supernovae, reactions with Trapped Particles on fast time scales establish equilibria that reduce the number of primitive variables required to evolve the Trapped particle component. On the other hand, a stationary-state approximation facilitates the treatment of the streaming particle component. Different approximations may apply in applications to stellar atmospheres, star formation, or cosmological radiative transfer. We compare the isotropic diffusion source approximation with Boltzmann neutrino transport of electron flavour neutrinos in spherically symmetric supernova models and find good agreement. An extension of the scheme to the multi-dimensional case is also discussed.
