Laguerre-Gaussian Vortex Beams Research Articles

Analysis of orbital angular momentum spectra of Hankel-Bessel beams in channels with oceanic turbulence

Beams with different-mode-number (l) orbital angular momenta (OAMs) are mutually orthogonal to each other, which makes it possible to enlarge the channel capacity in an OAM multiplexed underwater optical communication (UOC) system. Nevertheless, the implementation of this strategy is limited by oceanic turbulence. Hankel-Bessel (HB) vortex beams carrying OAM are relatively less affected by atmospheric turbulence due to their ability to propagate without changing the intensity profile (non-diffraction nature) and remarkable ability to be reconstructed after encountering an obstacle (self-healing mechanism). Consequently, HB vortex beams can be used as the carriers to increase the channel capacity of information transmission. In this paper, based on the Rytov approximation theory, the analytical expressions of OAM spectra for HB vortex beams under weak horizontal oceanic turbulent channels are derived. The influences of oceanic turbulence parameters on the OAM spectra of HB vortex beams are investigated via numerical calculations. The results indicate that oceanic turbulence leads to the decline of detection probability of transmitted OAM mode and the broadening of OAM spectra as well. Similarly, the spatial coherence length in oceanic turbulence decreases with increasing propagation distance and the dissipation rate of mean-squared temperature and with decreasing the dissipation rate of turbulent kinetic energy, which lead to the decline of detection probability of transmitted OAM mode for HB vortex beams. On the other hand, beams with larger OAM mode numbers each have a wider beam spreading after propagating in the turbulence, which results in the decrease of the detection probability for transmitted OAM modes of HB vortex beams. And the HB vortex beams are more affected by salinity fluctuation than by temperature fluctuations, which indicates that salinity fluctuations are much more effective than temperature fluctuations in determinating the effect of oceanic turbulence. In addition, for weak turbulence and a distance of several tens of meters, the transmission performance of HB vortex beams is worse than that of Laguerre-Gaussian vortex beams with the optimal waist setting. These results provide references for the realization of optical communication links in the marine environment.

Dimensional properties of Laguerre-Gaussian vortex beams.

We derive and analyze the dimensional properties of Laguerre-Gaussian vortex beams theoretically and numerically. The analytical expressions of inner and outer radii are given out and proved to be proportional to the transverse beam size, when the topological charge remains. The ratio of the outer and inner radius only depends on the topological charge, having nothing to do with the waist radius and the propagation distance, and the ratio decreases as the topological charge increases. Using a spatial light modulator loaded with computer-generated holograms, we generate vortex beams. The experimental results are in good agreement with our numerical simulations. This research may provide useful insights into the study of the optical vortex beam and its further applications.

Comparison of the stability of Laguerrе-Gauss vortex beams to random fluctuations of the optical environment

The propagation of Laguerre-Gauss vortex beams through a random phase distorting medium is numerically and experimentally investigated. The influence of the order of the mode on the degree of conservation of vortices of different orders in a random environment is analyzed. An increase in the stability of the detection of a vortex in a beam with a small defocusing of the output Fourier cascade of the optical correlator is shown experimentally.

Deep transmission of Laguerre-Gaussian vortex beams through turbid scattering media.

Light scattering and transmission of Gaussian (G) and Laguerre-Gaussian (LG) vortex beams with different orbital angular momentum (L) in various turbid media were investigated. Transmittance was measured with varied ratios of sample thickness (z) to scattering mean free path (ls) of turbid media, z/ls. In the ballistic region, the LG and G beams were found to have no significant difference on transmittance, while in the diffusive region, the LG beams showed a higher received signal than the G beams, and the LG beams with higher L values showed a higher received signal than those with lower L values. The transition points from ballistic to diffusive regions for different scattering media were determined. This newly observed transmittance difference of LG and G beams may be used for deep target detection in turbid media through LG beam imaging.

Measuring topological charges of Laguerre–Gaussian vortex beams using two improved Mach–Zehnder interferometers

Abstract. We demonstrate, theoretically and experimentally, a new method to measure high-order topologicalcharges (TCs) of Laguerre–Gaussian vortex beams, including the magnitude and the sign, by analyzing theinterference intensity patterns. The magnitude is determined by analyzing the interference intensity patternsbetween the vortex beam and its conjugate beam, and using an improved Mach–Zehnder interferometerwith a dove prism. Counting the number of interference bright petals attests to the magnitude of high-orderTCs through half of the bright petal number. After the TC is modulated by a spiral phase plate, the sign isacquired by comparing the counting results of two charge-coupled devices. Just by this method, we havebeen able to measure both the magnitude and the sign of the TCs up to l ¼ 90. Our experimental resultsare in good agreement with the numerical simulations. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)[DOI: 10.1117/1.OE.55.3.035104] Keywords: topological charge; interference; spiral phase plate; measurement.Paper 160085 received Jan. 18, 2016; accepted for publication Mar. 1, 2016; published online Mar. 22, 2016.

Light scattering of a Laguerre-Gaussian vortex beam by a chiral sphere.

Since the development of the generalized Lorenz-Mie theory, electromagnetic scattering by arbitrary beams has drawn growing interest. The Laguerre-Gaussian (LG) vortex beam is well known for its orbital angular momentum. With the aim of investigating the analytical solution to the scattering of a chiral sphere by a LG vortex beam, particular attention is paid to the expansion expression of the LG vortex beam. The expansion coefficients are derived based on the expansion of a Hermite Guassian beam as the LG vortex beam can be expressed as the superposition of Hermite Guassian modes. The numerical results of the incident beam expansion coefficients convergence and the scattered field comparison with the reference prove the validity of the theoretical analysis and computation codes. The results reveal that there exists an optimal sphere size for the maximum scattered field which is determined by the topological charge, beam waist radius, and beam center position. The investigation could provide a foundation for the optical manipulation of chiral particles by a LG vortex beam.

Numerical investigations of non-collinear optical parametric chirped pulse amplification for Laguerre–Gaussian vortex beam

We present for the first time a scheme to amplify a Laguerre–Gaussian vortex beam based on non-collinear optical parametric chirped pulse amplification (OPCPA). In addition, a three-dimensional numerical model of non-collinear optical parametric amplification was deduced in the frequency domain, in which the effects of non-collinear configuration, temporal and spatial walk-off, group-velocity dispersion and diffraction were also taken into account, to trace the dynamics of the Laguerre–Gaussian vortex beam and investigate its critical parameters in the non-collinear OPCPA process. Based on the numerical simulation results, the scheme shows promise for implementation in a relativistic twisted laser pulse system, which will diversify the light–matter interaction field.

High-order topological charges measurement of LG vortex beams with a modified Mach–Zehnder interferometer

We present a new method to measure the high-order topological charges (TCs) of Laguerre–Gaussian (LG) vortex beams by using a modified Mach–Zehnder interferometer. Counting the number of interference bright fringes between the LG beam and its conjugate beam determines integer and half-integer TCs through half of the bright fringe number. The proposed method can measure the order of the integer TC up to 90, which is higher than that achieved by previous methods. This technique opens up new applications for LG vortex beams.

Analysis of the radiation force of a Laguerre Gaussian vortex beam exerted on an uniaxial anisotropic sphere

Based on the expansion of Hermite Gaussian (HG) beam in terms of spherical vector wave functions (SVWFs) utilizing Complex Source Point Method (CSPM) and the relation between HG beam and Laguerre Gaussian (LG) mode, we derived the expansion of LG vortex beam in terms of SVWFs. Using Generalized Lorenz Mie Theory (GLMT), the radiation force (RF) exerted on a uniaxial anisotropic sphere by a LG vortex beam with spiral phase distribution is calculated. The effects of the radial and azimuthal mode index of LG vortex beam, anisotropic permittivity tensor elements, and particle size on the dimensionless axial and transverse RF have been numerically analyzed in detail.

拉盖尔高斯涡旋光束对生物细胞的散射特性分析

拉盖尔高斯涡旋光束对生物细胞的散射特性分析

Experimental study on multiple-ring vortex beams

The generation, propagation and application of vortex beams have been hot research topics in recent years. In this paper we introduce the novel multiple-ring vortex beams, including double-ring vortex beams and triple-ring vortex beams, which are generated by the coaxial superposition of multiple Laguerre-Gaussian vortex beams with different topological charge numbers and different waist parameters, and their intensity distribution is of multiple-ring. We study the generation and distribution characteristics of multiple-ring vortex beams theoretically, obtain the computer generated hologram of multiple-ring vortex beams based on conjugate symmetric extension Fourier computer generated holography, and experimentally generate quality multiple-ring vortex beams using a spatial light modulator. Excellent agreement between theoretical and experimental results is observed. The study indicates that each ring of multiple-ring vortex beams carries different orbital angular momentum, and the spatial distribution is independent. The novel multiple-ring vortex beams provide more controllable parameters and more diverse structure distributions, which enable their applications in the fields of micro-manipulation as optical tweezers or optical spanner. Furthermore, they also have potential applications as available encoding tools in optical communication.

Effect of atmospheric turbulence on the orbital angular momentum of hollow vortex beams

The phase fluctuation of Laguerre-Gaussian (LG) vortex beams induced by atmospheric turbulence affects the quantum phase associated with azimuth coordinates and affects the orbital angular momentum of the vortex beams. The measurement of orbital angular momentum is affected by the change in the classical phase and the quantum phase in the Hilbert space. This paper analyzes the additional random complex phase of the vortex beam generated by the atmospheric turbulence and discusses the effect of atmospheric turbulence on the orbital angular momentum of an LG vortex beam using the photon state-vector function. The distributions of the classical phase of vortex beams affected by turbulence of different strengths are calculated and compared with the case for LG vortex beams transmitted through free space. Results show that the atmospheric turbulence affects the phase value of LG vortex beams transmitted in the external field and significantly affects the beam phase structure in the near field. However, the effect of turbulence on the phase of vortex beams is insignificant for a transmission range z > 2000 m while the phase values vary slowly and gradually become constant.

Propagation of Laguerre-Gaussian vortex beam

For Laguerre Gaussian vortex beam, the analytical expression of the electric field is derived in the observation plane after propagation. Theoretical analysis shows that the definition of Gaussian beam is unsuitable to describing the size of the laguerre Gaussian vortex beam while propagation. It is more convenient that the radius of the point where intensity is maximum is used to define the vortex beam after propagation. Besides the beam broadening effect induced by diffraction, phase distribution exhibits special change in the observation plane. Isophase line changes from radial to arc. If the topological charge of the vortex beam is positive, the isophase line will bend clockwise after propagation; if the topological charge of the vortex beam is negative, the isophase line will bend anticlockwise.

Phase and interference properties of optical vortex beams

Laguerre-Gauss vortex beams carrying different topological charges are generated from Hermite-Gauss laser beams emitted by a gas laser, and their phase properties are explored by studying their interference with a plane wave. Interference of two Laguerre-Gauss vortex beams carrying equal but opposite topological charge is also studied by using a modified Mach-Zehnder interferometer. Experimentally recorded intensity profiles are in good agreement with the theoretically expected profiles.

Free-space propagation of second harmonic Laguerre–Gaussian beams carrying phase singularity

The vorticity of a free propagating second harmonic (SH) beam produced in a nonlinear quadratic crystal by a combined beam composed of two coaxial Laguerre–Gaussian vortex beams is analysed. In the near field of the SH radiation an aligned vortical structure with a number of double-charge vortices is created. The diffraction of the SH beam under free propagation is also discussed.

Free-space propagation of light field created by Bessel–Gauss and Laguerre–Gauss singular beams

The propagation of a combined beam consisting of two coaxial Bessel–Gauss and Laguerre–Gauss vortex beams is investigated. It is demonstrated that the vortical properties of light field under diffraction depend on propagation length as well as on amplitude ratio of individual beams. A transition of the topological charge of the light field caused by diffraction is revealed.