共查询到20条相似文献,搜索用时 15 毫秒
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Properties of an optical vortex light beam formed after the astigmatic telescopic transformation of a circular Laguerre-Gaussian mode are considered both theoretically and experimentally. The beam evolution is found to be in conformity with the general notions on the high-order optical vortex symmetry breakdown. Upon propagation, the asymmetric beam shows a sort of rotation of its transverse profile in accord with the energy circulation in the original circular mode; this process is described on the base of the beam intensity moments and the vortex and asymmetry components of its orbital angular momentum. An l-charged optical vortex converts into |l| secondary first-order vortices positioned on a straight line crossing the beam axis. Orientation of this straight line in the beam cross section and spatial separation of the secondary vortex cores depend on the propagation distance. Morphology (orientation and anisotropy) of all the secondary vortices is the same and depends on the propagation distance; the anisotropy can be characterized by the vortex component of the beam angular momentum. At certain distance, relative separation of secondary vortices with respect to the beam transverse size reaches its maximum that corresponds to the minimum anisotropy of the vortices. The results can be useful in the context of current research of the optical vortex arrays. 相似文献
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《中国物理 B》2019,(3)
It is widely accepted that an off-axis noncanonical vortex moves across the free-space diffracting Gaussian beam without rotation. But our analysis shows that the vortex swirls a while before it approaches infinite. By neglecting the divergence of the host beam, we focus on this rotation characteristics of the vortices in linear homogeneous media. For the symmetrical host beam, it is found that the vortex moves along an elliptical trajectory, while the topological charge and the angular momentum of the vortex core relative to the beam axis are conserved. For the asymmetrical host beam, the vortex trajectory is rather complicated, since the noncanonical parameter varies as the light propagates, resulting in topological charge inversion. But we find that the vortices are always confined in a rectangular area, and the rotation direction is determined by the topological charge. 相似文献
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The propagation of a pair of vortices nested in a Gaussian beam through a tilted lens is studied. It is shown that after passing through the tilted lens, the relation between the transverse position of vortices and the tilt coefficient is linear in the propagation for isopolar vortex pair and vortex dipole, and in the three-dimensional (3D) case the vortex trajectories are sometimes like U or X shapes. With increasing the orientation angle of the vortex pair, the trajectories of vortices are circles for the both cases. The overlap of vortices may take place for the isopolar vortex pair, while the annihilation and revival of vortices occur for the vortex dipole in the propagation. 相似文献
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Josserand C 《Chaos (Woodbury, N.Y.)》2004,14(3):875-881
We show how giant vortices can be stabilized for strong external potentials in Bose-Einstein condensates. We illustrate the formation of these vortices thanks to the Ginzburg-Landau dissipative dynamics for two typical potentials in two spatial dimensions. The giant vortex stability is studied for the particular case of a rotating cylindrical hard wall. Due to axial symmetry the minimization of the perturbed energy is simplified into a one dimensional relaxation dynamics. Solving this 1D minimization problem, we observe that giant vortices are either never stable, or only stable in a finite frequency range. Finally we obtain the marginal curve for the minimum frequency needed to observe a giant vortex. 相似文献
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In view of wide applications of structured light fields and plasmonic vortices, we propose the concept of compound plasmonic vortex and design several structured plasmonic vortex generators. This kind of structured plasmonic vortex generators consists of multiple spiral nanoslits and they can generate two or more concentric plasmonic vortices. Different from Laguerre–Gaussian beam, the topological charge of the plasmonic vortex in different region is different. Theoretical analysis lays the basis for the design of radially structured plasmonic vortex generators and numerical simulations for several examples confirm the effectiveness of the design principle. The discussions about the interference of vortex fields definite the generation condition for the structured vortex. This work provides a design methodology for generating new vortices using spiral nanoslits and the advanced radially structured plasmonic vortices is helpful for broadening the applications of vortex fields. 相似文献
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Based on the Rytov approximation and the cross-spectral density approximation for the mutual coherence function of the partially coherent field, the propagation properties of the partially coherent beams with optical vortices in turbulent atmosphere are discussed. The average intensity and the mutual coherence function of the partially coherent vortex beams propagation in weak turbulent atmosphere are obtained.It is shown that the vortex structure of the average cross-spectral density of partially coherent beams has the same helicoidally shape as that of the phase of the fully coherent Laguerre-Gauss beams in free space and the relative intensity of the beam is degraded by optical vortex. 相似文献
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Kerr RM 《Physical review letters》2011,106(22):224501
A pair of perturbed antiparallel quantum vortices, simulated using the three-dimensional Gross-Pitaevskii equations, is shown to be unstable to vortex stretching. This results in kinetic energy K(?ψ) being converted into interaction energy E(I) and eventually local kinetic energy depletion that is similar to energy decay in a classical fluid, even though the governing equations are Hamiltonian and energy conserving. The intermediate stages include the generation of vortex waves, their deepening, multiple reconnections, the emission of vortex rings and phonons, and the creation of an approximately -5/3 kinetic energy spectrum at high wave numbers. All of the wave generation and reconnection steps follow from interactions between the two original vortices. A four vortex example is given to demonstrate that some of these steps might be general. 相似文献
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T.C. Wu R. Cao T.J. Yang Lance Horng J.C. Wu Jan Kolá?ek 《Solid State Communications》2010,150(5-6):280-284
Superconducting Nb thin films with a spacing-graded array of holes were prepared by electron beam lithography. Two films with different hole gradients were fabricated. The ac-driven vortices were investigated in Nb superconductors with a spacing-graded array of holes. The measurements revealed pronounced rectified voltage when the vortex lattice is driven by an ac injected current. The rectified voltage is mainly caused by the strength of the vortex–vortex interaction. The rectified motion of a vortex is affected by the pinning potential of the spacing-graded array and the applied magnetic field. The vortex–vortex interaction strength changes the effective pinning landscape of the vortices and an asymmetric potential is formed. Vortices depin easily from high concentration to low concentration of pinning sites. In both samples, the ac-driven vortices exhibit a variety of dynamical responses and the rectified voltage is tunable with the applied magnetic field. 相似文献
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Composite coherence vortices and their propagation in free space 总被引:1,自引:0,他引:1
Taking Gaussian Schell-model (GSM) background vortex beams as an example of partially coherent vortex beams, the composite coherence vortices resulting from the superposition of the cross-spectral density function of two parallel, noncollinear partially coherent vortex beams and their propagation in free space are studied, and the main attention is paid to the effect of relative off-axis distance, coherence parameter and propagation distance on the composite coherence vortices. The number and location of composite coherence vortices vary by changing the relative off-axis distance, coherence parameter or propagation distance. In the coherent limit, the composite coherence vortex becomes the composite optical vortex. 相似文献
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Xiumin Gao Jiancheng Yu Maojin Yun Hanming Guo Jian Wang Songlin Zhuang Boming Cao 《Optik》2012,123(2):144-146
Optical vortices have attracted much attention recently due to their novel properties and widening applications. And lots of optical vortices can be obtained though most of them turn on spiral pattern on increasing azimuthal angle. In this paper, one kind of non-spiral optical vortex was proposed whose front phase distribution is tangent function of azimuthal angle. And this kind of optical vortices were also observed experimentally by computer-generated hologram method. It was found that when topological charge is smaller than unit one, vortex beam shape changes considerably on increasing topological charge, from hollow pattern to curve shape. When topological charge is bigger than unit and is times of 0.5, vortex beam turns symmetrical polygonal pattern though there is crack between adjacent sides, and the side number is twice of topological charge. 相似文献
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Qiansen Xie 《Optics Communications》2008,281(1):7-11
We analyze the characterizations of the optical vortices generated by a multi-level achromatic spiral phase plate. The effective topological charge of the multi-level fractional spiral phase plate is expanded into Fourier series and the analytical formula of the relative intensity of each component is obtained. It is shown that the fractional part of the topological charge sharply reduces the purity of vortices. Using the 36 levels achromatic spiral phase plate, we can obtain a vortex beam with purity larger than 95% across a bandwidth exceeding 140 nm in the visible region of the spectrum. 相似文献
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《Optics Communications》2003,215(1-3):1-9
A vorticity of free propagating SH beam produced in nonlinear crystal by combined beam composed of two coaxial Laguerre–Gaussian vortex beams is analyzed. It is revealed that the vortical structures of SH beam in the near and far fields are different when two vortex beams are carrying vortices with topological charges of different signs. The diffraction of SH beam under free propagation is investigated. A qualitative agreement of the theoretical predictions with experimental results is obtained. 相似文献
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A triangular aperture illuminated with a vortex beam creates a truncated lattice diffraction pattern that identifies the charge of the vortex. In this Letter, we demonstrate the measurement of vortex charge via this approach for vortex beams up to charge ±7. We also demonstrate the use of this technique for measuring femtosecond vortices and noninteger vortices, comparing these results with numerical modeling. It is shown that this technique is simple and reliable, but care must be taken when interpreting the results for the noninteger case. 相似文献
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This paper addresses the drag force and formation of vortices in the boundary layer of a Bose-Einstein condensate stirred by a laser beam following the experiments of Phys. Rev. Lett. 83, 2502 (1999)]. We make our analysis in the frame moving at constant speed where the beam is fixed. We find that there is always a drag around the laser beam. We also analyze the mechanism of vortex nucleation. At low velocity, there are no vortices and the drag has its origin in a wakelike phenomenon: This is a particularity of trapped systems since the density gets small in an extended region. The shedding of vortices starts only at a threshold velocity and is responsible for a large increase in drag. This critical velocity for vortex nucleation is lower than the critical velocity computed for the corresponding 2D problem at the center of the cloud. 相似文献
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Zhiguo Wang Zhiyu Hu Yuan Zhang Rui Zheng Tiancong Liu Yanpeng Zhang 《Annalen der Physik》2023,535(5):2200652
Introducing vortices into an Airy beam by the interference between the lobes of the Airy beam for the first time, the modulation of Airy vortices is experimentally and theoretically investigated by electromagnetically induced transparency (EIT) effect and changing the number of side lobes of the Airy beam. The formation and disappearance of vortices in Airy beams can be caused by changing the number of side lobes. The EIT effect can induce the movement of vortex phase singularity by regulating the intensities of lobes in Airy beams. However, changing the number of side lobes can change the energy distribution of the lobes through the energy flow due to the self-healing of Airy beams, thus causing the displacement of vortex phase singularity. In addition, the simulation of the Poynting vector shows that the less the side lobes are blocked, the more energy can be retained in the main lobe and the unblocked side lobes, so that the overall shape of the Airy beam can be better maintained. Such studies provide a new method to acquire and adjust Airy vortex beams and can be applied in the realm of optical micromanipulation. 相似文献
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We demonstrate simultaneous generation, propagation and detection of optical vortices using all fiber-optic system. A fiber-optic Y-coupler was used for generating spherical and doughnut beams, simultaneously. Gaussian (TEM00) beam emitted from CW red He-Ne laser is coupled into the fiber coupler and is converted into vortex beam via second arm of fiber which propagates with azimuthal phase dependence having well defined orbital angular momentum. The phase structure of vortex beam was detected by interfering both the beams using simple fiber-optic interferometer. The present all fiber-optic system might find application for detecting, sensing physical parameters and is simple and cost effective for generating and detecting optical vortices. 相似文献
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Study correlation vortices in the near-field of partially coherent vortex beams diffracted by an aperture
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We have derived the analytical expression of the electric cross-spectral density in the near-field of partially coherent vortex beams diffracted by an aperture. Taking the Gaussian Schell-model vortex beam as a typical example of partially coherent vortex beams, the spatial correlation properties and correlation vortices in the near-field of partially coherent vortex beams diffracted by a rectangle aperture are studied. It is shown that the off-axis displacement, spatial degree of coherence parameter, propagation distance, and the opening factor of the aperture affect the spectral degree of coherence and positions of correlation vortices. With the optimization algorithm, we obtain the symmetric distributing coherent vortex. 相似文献