Charged Vortices Research Articles

Switching the Topological Charge of Surface Plasmon Vortex by Tailoring Polarization States

We demonstrate dynamically switching the topological charge of surface plasmon (SP) vortex in gold metasurfaces by altering the polarization states of incident light. Two SP vortex sources with different helicity are created by the optimized L-shaped and ‘+’-shaped nanoslits with right-handed circular polarized and linear polarized excitations, respectively. By elaborately arraying the nanoslits to form a circle, the topological charge of the created SP vortex can be switched from −1 to 1 via altering the polarization states of incident light from circular to linear. Moreover, based on such a strategy, the topological charge can be switched from 0 to 2 by elaborately arraying the nanoslits to form an Archimedes spiral. These results provide the extra degree of freedom to modulate the topological charge of SP vortex, promising practical applications in optical communication, particle trapping, and integrated photonic circuits.

Dynamics of phase separation in two-species Bose-Einstein condensates with vortices

We examine the dynamics associated with the miscibility-immiscibility transition of trapped two-component Bose-Einstein condensates (TBECs) of dilute atomic gases in presence of vortices. In particular, we consider TBECs of Rb hyperfine states, and Rb-Cs mixture. There is an enhancement of the phase-separation when the vortex is present in both condensates. In the case of a singly charged vortex in only one of the condensates, there is enhancement when the vortex is present in the species which occupy the edges at phase-separation. But, suppression occurs when the vortex is in the species which occupies the core region. To examine the role of the vortex, we quench the inter-species interactions to propel the TBEC from miscible to immiscible phase, and use the time dependent Gross-Pitaevskii equation to probe the phenomenon of phase-separation. We also examine the effect of higher charged vortex.

Energy flux density and angular momentum density of radial Pearcey-Gauss vortex array beams in the far field

The longitudinal and transverse energy flux density (EFD) and angular momentum density (AMD) of the radial Pearcey-Gauss vortex array beams are studied by using the vector angular spectrum representation and stationary phase method, where the influence of topological charge, initial phase index, noncanonical strength and the number of beamlet on far-field vectorial structures of the corresponding beam is emphasized. The results show that the topological charge of center optical vortex is always equal to initial phase index for different noncanonical strength. The longitudinal EFDs exhibit different structures by varying initial phase index and the number of beamlet. For an odd-N, the topological charge of center optical vortex can be determined by distinguishing the longitudinal EFD, however for an even-N the topological charge cannot be identified due to the equivalence of longitudinal EFD in the case of positive and negative initial phase index m. The AMD tends to split more branches from the positive and negative direction with increasing the absolute value of topological charge l, The inner structures of AMD are also affected by different beamlets while the zero value of AMD is always retained.

Vinen turbulence via the decay of multicharged vortices in trapped atomic Bose-Einstein condensates

We investigate a procedure to generate turbulence in a trapped Bose-Einstein condensate which takes advantage of the decay of multicharged vortices to reduce surface oscillations. We show that the resulting singly charged vortices twist around each other, intertwined in the shape of helical Kelvin waves, which collide and undergo vortex reconnections, creating a disordered vortex state. By examining the velocity statistics, the energy spectrum, the correlation functions, and the temporal decay and comparing these properties with the properties of classical turbulence and observations in superfluid helium, we conclude that this disordered vortex state can be identified with the Vinen regime of turbulence which has been discovered in the context of superfluid helium.

Tight Focusing Properties of Azimuthally Polarized Pair of Vortex Beams through a Dielectric Interface

Tight focusing properties of an azimuthally polarized Gaussian beam with a pair of vortices through a dielectric interface is theoretically investigated by vector diffraction theory. For the incident beam with a pair of vortices of opposite topological charges, the vortices move toward each other, annihilate and revive in the vicinity of focal plane, which results in the generation of many novel focal patterns. The usable focal structures generated through the tight focusing of the double-vortex beams may find applications in micro-particle trapping, manipulation, and material processing, etc.

Control the Raman response of individual carbon nanotubes by orbital angular momentum of light.

We propose and demonstrate an approach for tailoring the Raman response of an individual single-walled carbon nanotube (SWNT) by employing the optical vortex as the excitation. Specifically, we observe the blueshifts of radial breathing mode and G mode when the topological charge of the vortex beam is increased from 0 to 5. Further theoretical analysis yields that the optical absorption and the corresponding laser heating effect of SWNT are inversely proportional to the topological charge of the optical vortex. Such a decrease in the laser heating effect weakens the softening of C-C bonds, leading to the blueshifts of Raman modes.

Controlled noncanonical vortices from higher-order fractional screw dislocations.

A pair of stable noncanonical scalar vortices of the same charge is generated experimentally across the cross section of an optical beam using a computer-generated hologram with higher-order fractional screw dislocation. The noncanonical nature of the generated vortices is identified by the gradient of the phase around each vortex and also the crossing angle between the zero contours of the real and imaginary parts of the optical field. The anisotropy of the vortices is controlled by the fractional order of the computer-generated hologram. The behavior of the rate of change of phase around each individual vortex is found to be different from that of the earlier reports on noncanonical vortices. The observed experimental results are qualitatively explained based on the effect of nonlocalized phases of the generated vortices. The generated beams with a nested pair of noncanonical vortices can be of importance in accelerated rotation of the beams and in optical micromanipulation.

Dielectric geometric phase optical elements fabricated by femtosecond direct laser writing in photoresists

We propose to use a femtosecond direct laser writing technique to realize dielectric optical elements from photo-resist materials for the generation of structured light from purely geometrical phase transformations. This is illustrated by the fabrication and characterization of spin-to-orbital optical angular momentum couplers generating optical vortices of topological charge from 1 to 20. In addition, the technique is scalable and allows obtaining microscopic to macroscopic flat optics. These results thus demonstrate that direct 3D photopolymerization technology qualifies for the realization of spin-controlled geometric phase optical elements.

Effect of Chern-Simons dynamics on the energy of electrically charged and spinning vortices

We study the effect of a Chern-Simons term on the electrically charged and spinning solitons of several $U(1)$ gauged models in $2+1$ dimensions. These are vortices of complex scalar field theories, both with and without symmetry breaking dynamics, and the $O(3)$ Skyrme model. In all cases the gauge decoupling limits are also considered. It is well known that the effect of the Chern-Simons dynamics is to endow vortices with electric charge $Q_e$ and spin $J$, but our main aim here is to reveal a new feature: that the mass-energy $E$ of the electrically charged vortex can be lower than that of the electrically neutral one, in contrast to the usual monotonic increase of $E$ with $Q_e$. These effects of Chern-Simons dynamics were observed previously in $3+1$ dimensional systems, and the present results can be viewed as corroborating the latter. Moreover, the usual energy-spin relationship is likewise altered. We carry out a detailed quantitative analysis of azimuthally symmetric vortices and describe their qualitative features by constructing the solutions numerically.

Relativistic Electron Vortices.

The desire to push recent experiments on electron vortices to higher energies leads to some theoretical difficulties. In particular the simple and very successful picture of phase vortices of vortex charge ℓ associated with ℓℏ units of orbital angular momentum per electron is challenged by the facts that (i)the spin and orbital angular momentum are not separately conserved for a Dirac electron, which suggests that the existence of a spin-orbit coupling will complicate matters, and (ii)that the velocity of a Dirac electron is not simply the gradient of a phase as it is in the Schrödinger theory suggesting that, perhaps, electron vortices might not exist at a fundamental level. We resolve these difficulties by showing that electron vortices do indeed exist in the relativistic theory and show that the charge of such a vortex is simply related to a conserved orbital part of the total angular momentum, closely related to the familiar situation for the orbital angular momentum of a photon.

Generation and Validation of Topological Charges of High-Power Gyrotron Orbital Angular Momentum Beams From Phase Retrieval Algorithm

We present a phase coefficient optimization technique for determining the vortex charge of a high-power orbital angular momentum beam. This high-power vortex beam is generated by transmitting a Gaussian-like beam emitted by a gyrotron with an output power of 25 kW through a spiral phase plate (SPP), which introduces a vorticity at the center of the beam characterized by the geometrical parameters of the SPP. One rigorous, intensity-measurement-based, phase retrieval technique, known as the Gerchberg–Saxton algorithm, does not converge to a correct solution because of the presence of a phase singularity in the high-power vortex beam. Here, we introduce a new phase retrieval algorithm that chooses an appropriate initial phase estimate. This technique yields successful vortex charge determination for both low- and high-power vortex beams. The retrieved intensity profiles show 99.51% and 99.27% intensity regeneration at measurement planes with optimized initial phase estimates for the low- and high-power beams, respectively.

Fractional-topological-charge-induced vortex birth and splitting of light fields on the submicron scale

The formation and dynamics of fractional vortex charge in orbital-angular-momentum states is experimentally investigated. The holographic lithography method developed in this work may be effectively applied to study other structured matter waves.

A novel measuring method for arbitrary optical vortex by three spiral spectra

In this letter, the topological charge of non-integer vortices determined by three arbitrary spiral spectra is theoretically demonstrated for the first time. Based on the conclusion, a novel method to measure non-integer vortices is presented. This method is applicable not only to arbitrary non-integer vortex but also to arbitrary integer vortex.

Linear and angular momenta in tightly focused vortex segmented beams of light (Invited Paper)

We investigate the linear momentum density of light, which can be decomposed into spin and orbital parts, in the complex three-dimensional field distributions of tightly focused vortex segmented beams. The chosen angular spectrum exhibits two spatially separated vortices of opposite charge and orthogonal circular polarization to generate phase vortices in a meridional plane of observation. In the vicinity of those vortices, regions of negative orbital linear momentum occur. Besides these phase vortices, the occurrence of transverse orbital angular momentum manifests in a vortex charge-dependent relative shift of the energy density and linear momentum density.

倍频过程中复合涡旋拓扑荷数的倍频效应

倍频过程中复合涡旋拓扑荷数的倍频效应

In situ measurement of the topological charge of a perfect vortex using the phase shift method.

We propose a method to determine the topological charge (TC) of a perfect vortex. With the phase shift technique, the perfect vortex and its conjugate beam exactly overlap and interfere. Consequently, the TC of a perfect vortex is determined by counting the number of interference fringes. This proposed method enables in situ determination of the TC of the perfect vortex without the need for additional optical elements, and it is immune to environmental vibration and parasitic interference.

The effect of phase assemblages, grain boundaries and domain structure on the local switching behavior of rare-earth modified bismuth ferrite ceramics

Piezoelectric properties and ferroelectric/ferroelastic domain switching behavior of polycrystalline ceramics are strongly influenced by local scale (i.e. <100 nm) phenomena, such as, the phase assemblages, domain structure, and defects. The method of ceramic synthesis strongly effects the local properties and thus plays a critical role in determining the macroscopic ferroelectric and piezoelectric performance. The link between synthesis and local scale properties of ferroelectrics is, however, rarely reported, especially for the emerging lead-free materials systems. In this work, we focus on samarium modified bismuth ferrite ceramics (Bi0.88Sm0.12FeO3, BSFO) prepared by two methods: standard solid state reaction (SSR) and mechanochemi≿ally assisted synthesis (MAS). Each ceramic possesses different properties at the local scale and we used the piezoresponse force microscopy (PFM) complemented by transmission electron microscopy (TEM) to evaluate phase distribution, domain structure and polarization switching to show that an increase in the anti-polar phase assemblages within the polar matrix leads to notable changes in the local polarization switching. SSR ceramics exhibit larger internal bias fields relative to the MAS ceramics, and the grain boundaries produce a stronger effect on the local switching response. MAS ceramics were able to nucleate domains at lower electric-fields and grow them at faster rates, reaching larger final domain sizes than the SSR ceramics. Local evidence of the electric-field induced phase transition from the anti-ferroelectric Pbam to ferroelectric R3c phase was observed together with likely evidence of the existence of head-to-head/tail-to-tail charged domain walls and domain vortex core structures. By comparing the domain structure and local switching behavior of ceramics prepared by two different methods this work brings new insights the synthesis-structure-property relationship in lead-free piezoceramics.

Cultivation of lemon fields.

The sign rule requires that adjacent singularities on a contour have opposite signs and hence cultivation of lemon only fields poses problem as all lemons have positive index. In this paper we show that the interference of three linearly polarized plane waves can create regions of ellipse and vector fields in 2-dimensions (2D) in which a lemon lattice is interlaced in a V-point lattice. The lemons appear at intensity maxima of the lattice structure while the V-points take care of index conservation by sitting at intensity minima. In the Stokes field S12, lemons and disclinations (V-points) appear as phase vortices of topological charge + 1 and -2 respectively. In the polarization distribution the constant azimuth lines (a-lines) are seen running through lemon and disclination alternatively obeying the sign rule [24]. We envisage that such polarization lattice structure may lead to novel concept of structured polarization illumination methods in super resolution microscopy.

Twisted non-Abelian vortices

Twisted non-Abelian flux-tube solutions are considered in the bosonic sector of a 4-dimensional [Formula: see text] super-symmetric gauge theory with U(2)[Formula: see text] symmetry, with two scalar doublets in the fundamental representation. Twist refers to a time-dependent matrix phase between the two doublets, and twisted strings have nonzero (global) charge, momentum, and in some cases even angular momentum per unit length. The planar cross section of a twisted string corresponds to a rotationally symmetric, charged non-Abelian vortex, satisfying 1st order Bogomolny-type equations and Gauss-type constraints. Quite unexpectedly some twisted strings lack cylindrical symmetry in [Formula: see text].

Nonperturbative Twist in the Generation of Extreme-Ultraviolet Vortex Beams.

High-order harmonic generation (HHG) has been recently proven to produce extreme-ultraviolet (XUV) vortices from the nonlinear conversion of infrared twisted beams. Previous works have demonstrated a linear scaling law of the vortex charge with the harmonic order. We demonstrate that this simple law hides an unexpectedly rich scenario for the buildup of orbital angular momentum (OAM) due to the nonperturbative behavior of HHG. The complexity of these twisted XUV beams appears only when HHG is driven by nonpure vortex modes, where the XUV OAM content is dramatically increased. We explore the underlying mechanisms for this diversity and derive a general conservation rule for the nonperturbative OAM buildup. The simple scaling found in previous works corresponds to the collapse of this scenario for the particular case of pure (single-mode) OAM driving fields.