Controlled noncanonical vortices from higher-order fractional screw dislocations

Maji, Satyajit; Brundavanam, Maruthi M.

doi:10.1364/ol.42.002322

Cited by 21 publications

(17 citation statements)

References 17 publications

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“…As illustrated in figure 2(a), this state is defined by a petal structure rotating at a constant rate [24][25][26][27] with propagation distance, given by f = D Dl k z . When the anisotropic parameter is non-zero (D>0), the rate at which the wavefunction's petal structure rotates begins to vary upon propagation [28][29][30], thus resulting in an angularly accelerating and decelerating electron wave, as shown in figures 2(b), (c). The dynamics of this wavefunction can be more easily grasped when equation (2) is rearranged into the following form …”

Section: Description Of Coiling Electron Beamsmentioning

confidence: 99%

Coiling free electron matter waves

et al. 2019

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Here we demonstrate particle beams that spiral in free space devoid of external fields. The beams consist of electrons in two lobes that twist around each other along the optical axis, such that each electron can be described by a two-lobed probability distribution that rotates as it propagates. Furthermore, we demonstrate that this twisting distribution can undergo programmed periods of angular acceleration. These unusual states are produced by preparing each free electron wavefunction in a superposition of non-diffracting Bessel modes that carry orbital angular momentum using nanofabricated diffraction holograms. The holograms can encode nonlinear azimuthal phase so that the resulting electron probability distribution twists in space in a controllable manner, accelerating and decelerating during propagation, without any radiation. This work provides a new platform to explore the dynamics of electrons in magnetic fields, and opens the possibility of producing other types of particle beams with coiling geometries.

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Section: Description Of Coiling Electron Beamsmentioning

confidence: 99%

Coiling free electron matter waves

et al. 2019

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“…There, the 'noncanonical' vortices were also called 'anisotropic' vortices [14,15], since not only the phase but also the amplitude of such vortices were spatially anisotropic. Perhaps this anisotropic structure limited the study of these vortices theoretically and experimentally, so the noncanonical vortices were visited rarely in recent years [16]. In this article, we will propose a new type of noncanonical vortices which is easy to construct and its focusing properties will also be discussed.…”

Section: Introductionmentioning

confidence: 97%

X-type vortex and its effect on beam shaping

Pang,

Xiao,

Zhang

et al. 2021

Preprint

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In this article we propose a new type of optical vortex, the X-type vortex. This vortex inherits and develops the conventional noncanonical vortex, i.e., it no longer has a constant phase gradient around the center, while the intensity keeps invariant azimuthally. The strongly focusing properties of the X-type vortex and its effect on the beam shaping in three-dimensional (3D) fields are analyzed. The interesting phenomena, which cannot be seen in canonical vortices, are observed, for instance the 'switch effect' which shows that the intensity pattern can switch from one transverse axis to another in the focal plane by controlling the phase gradient parameter. It is shown that by adjusting the phase gradient of this vortex, the focal field can have marvelous patterns, from the doughnut shape to the shapes with different lobes, and the beam along propagation direction will form a twisting shape in 3D space with controllable rotation direction and location. The physical mechanisms underlying the rule of the beam shaping are also discussed, which generally say that the phase gradient of the X-type vortex, the orbital angular momentum, the polarization and the 'nongeneric' characteristic contribute differently in shaping fields. This new type of vortex may supply a new freedom for tailoring 3D optical fields, and our work will pave a way for exploration of new vortices and their applications.

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“…The fractional OV (FOV) beams have intricate optical current flow across the beam and both extrinsic and intrinsic OAM [25][26][27][28]. The FOV beams have an overall and near-core anisotropic field distribution [25,29], and a broad OAM spectrum which is useful in high-dimensional entanglement [30], digital spiral imaging [31] and novel trapping applications [32].…”

Section: Introductionmentioning

confidence: 99%

Localized geometric phase analogue associated with Poincaré beams due to unfolding of fractional optical vortex beams through a birefringent crystal

Maji¹,

Pattanayak²,

Brundavanam³

2020

J. Opt.

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Fractional optical vortex beam is generated by the diffraction of a Gaussian beam using computer generated hologram embedded with mixed screw-edge dislocation. Unfolding of the generated fractional vortex beam into eigen-polarization components with orthogonal polarization results in the conversion of scalar phase singularity to vector polarization singularities in the beam cross-section. The evolution of the singularities of the ellipse field namely C-points (points of undefined major axis) and L-lines (lines of undefined handedness) in the state of polarization distribution on a transverse plane quantifies the transformation. The effect of the phase morphology dictated by the fractional order of the dislocation, transverse spatial separation and longitudinal relative phase of the two eigen-polarization components on determining the complex transverse polarization structure is investigated. The nature of the generated Poincaré beam is also indicated by projecting the states of polarization on to the Poincaré sphere. With increasing order of dislocation from 0.0 to 1.0 in fractional steps and with increasing relative phase, the partial Poincaré beam is transformed to a full Poincaré beam. The transformation of the local structure around the C-points is measured through the geometric phase due to the Poincaré sphere contour around the C-points for different dynamic phase difference of the unfolded FOV beams generated from different fractional order of dislocation. This study can be useful for different geometric phase based application of optical vortex beams.

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Controlled noncanonical vortices from higher-order fractional screw dislocations

Cited by 21 publications

References 17 publications

Coiling free electron matter waves

Coiling free electron matter waves

X-type vortex and its effect on beam shaping

Localized geometric phase analogue associated with Poincaré beams due to unfolding of fractional optical vortex beams through a birefringent crystal

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