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In this paper, we obtain the intensity and phase distributions of the scattering and external fields of a vector Bessel–Gaussian vortex beam in the far-field region after being scattered by a particle. In our analysis, we use the Generalized Lorenz–Mie theory (GLMT) and the angular spectrum decomposition method (ASDM). The orbital angular momentum (OAM) spectra of the fields are analyzed by using the spiral spectrum expansion method, which is a frequently used tool for studying the propagation of vortex beams in turbulent atmospheres. Both scattered and external fields show a significant difference in spiral spectra for particles with different characteristic parameters, such as the size and complex refractive index. We also examine sampling the phase along with a circle and show that it is unable to fully express the information of the fields. This study can provide a theoretical basis for the inversion of characteristic parameters of the Bessel–Gaussian vortex beam and spherical particle by OAM spectra with applications in remote sensing engineering. [ABSTRACT FROM AUTHOR]

In the framework of the generalized Lorenz–Mie theory (GLMT), the optical force and torque on a graphene-coated gold nanosphere by a vector Bessel beam are investigated. The core of the particle is gold, whose dielectric function is given by the Drude–Sommerfeld model, and the coating is multilayer graphene with layer number N, whose dielectric function is described by the Lorentz–Drude model. The axial optical force F z and torque T z are numerically analyzed, and the effects of the layer number N, wavelength λ , and beam parameters (half-cone angle α 0 , polarization, and order l) are mainly discussed. Numerical results show that the optical force and torque peaks can be adjusted by increasing the thickness of the graphene coating, and can not be adjusted by changing α 0 and l. However, α 0 and l can change the magnitude of the optical force and torque. The numerical results have potential applications involving the trapped graphene-coated gold nanosphere. [ABSTRACT FROM AUTHOR]

Highlights • The optical force on a charged sphere by a vector Bessel beam is investigated in the framework of GLMT. • The emergence of a pulling force and its dependence on α 0 , order, polarization, and ka are discussed. • The ratios of axial RPCS for charged and neutral spheres are computed to investigate the effect of surface charge. • The optical forces on a relatively small sphere (a = 10 nm) are computed, and the effects of α 0 , order, polarization, and ka are discussed. Abstract Optical tractor beams can reel in an object towards the source, and are becoming a topic of significant worldwide research. Previous works considered the axial and transverse radiation pressure cross-sections (RPCSs) of optical tractor Bessel polarized beams on a dielectric sphere. However, most particles are charged, and it is important to investigate the tractor beam effect on charged particles. The aim of this work is therefore directed toward this goal, where the axial and transverse RPCSs for a charged sphere illuminated by a vector Bessel beam are computed in the framework of generalized Lorenz-Mie theory (GLMT). Numerical computations of the RPCSs are performed, with emphasis on the emergence of a negative pulling force and its dependence on the half-cone angle α 0 , the order l , and the polarization. A higher-order (l ≠ 0) Bessel beam possesses a hollow core and is of vortex nature, while the fundamental mode (l = 0) is of non-vortex type and has a bright maximum intensity at the center of the beam. In our calculation, both l = 0 and l = 1 are considered. The axial PRCSs versus ka and α 0 are first calculated, and the negative axial forces can arise. Moreover, the axial and transverse RPCSs in the plane perpendicular to the beam axis are computed. However, numerical results show that the RPCSs are same to that for a neutral particle. To explain this, the ratios of axial RPCSs for charged and neutral spheres are investigated taking ka as a parameter. The results show that charges only affect the RPCSs for small particles. Finally, the RPCSs for a charged sphere of relatively small are considered. The charge can affect the magnitude of the RPCSs, however, it does not affect the direction of axial optical forces. These results are of great importance in the development of novel optical tweezers and tractor beams. [ABSTRACT FROM AUTHOR]

The interaction of a vector Bessel vortex beam (VBVB) with a charged sphere is investigated using generalized Lorenz–Mie theory (GLMT). The charges carried by the sphere are expressed by the surface conductivity σ s . The incident VBVBs are expanded using a series of beam shape coefficients (BSCs), whose analytical expressions are derived using the angular spectrum decomposition method (ASDM). The expanded coefficients of the scattered fields are calculated by considering the boundary conditions on the surface of the sphere, which are different from that for the case of neutral sphere. The effects of the carried charges on the scattering, absorption, and extinction coefficients are considered, with particular emphasis on the effect of the order, polarization, and half-cone angle of the beams. Various polarizations including linear, circular, radial, azimuthal, and mixed polarizations are considered. Numerical results show that the scattering, extinction, and absorption efficiencies are very sensitive to the beam parameters including polarization, half-cone angle, and order. Thus in practice, the scattering, extinction, and absorption caused by charged particles can be enhanced or reduced by choosing proper beam parameters according to practical demand. Such results have many potential applications. For instance, it is of help to improve the quality of wireless communication by reducing the attenuation caused by charged particles. It can also improve the precision for particle sizing using phase Doppler anemometry by enhancing the scattering of charged spheres. [ABSTRACT FROM AUTHOR]

The optical spin torque (OST) induced by vector Bessel (vortex) beams can cause a particle to rotate around its center of mass. Previous works have considered the OST on a Rayleigh absorptive dielectric sphere by a vector Bessel (vortex) beam, however, it is of some importance to analyze the OST components for a sphere of arbitrary size . In this work, the generalized Lorenz-Mie theory (GLMT) is used to compute the OST induced by vector Bessel (vortex) beams on an absorptive dielectric sphere of arbitrary size, with particular emphasis on the beam order, the polarization of the plane wave component forming the beam, and the half-cone angle. The OST is expressed as the integration of the moment of the time-averaged Maxwell stress tensor, and the beam shape coefficients (BSCs) are calculated using the angular spectrum decomposition method (ASDM). Using this theory, the OST exerted on the light-absorptive dielectric sphere in the Rayleigh, Mie or the geometrical optics regimes can be considered. The axial and transverse OSTs are numerically calculated with particular emphasis on the sign reversal of the axial OST and the vortex-like character of the transverse OST, and the effects of polarization, beam order, and half-cone angle are discussed in detail. Numerical results show that by choosing an appropriate polarization, order and half-cone angle, the sign of the axial OST can be reversed, meaning that the sphere would spin in opposite handedness of the angular momentum carried by the incident beam. The vortex-like structure of the total transverse OSTs can be observed for all cases. When the sphere moves radially away from the beam axis, it may rotate around its center of mass in either the counter-clockwise or the clockwise direction. Conditions are also predicted where the absorptive sphere experiences no spinning. Potential applications in particle manipulation and rotation in optical tweezers and tractor beams would benefit from the results. [ABSTRACT FROM AUTHOR]

The interaction of an axicon-generated vector Bessel beam (AGVBB) with a homogeneous sphere is investigated in the framework of generalized Lorenz-Mie theory (GLMT). An analytical expression of beam shape coefficients (BSCs) is derived using angular spectrum decomposition method (ASDM), and the scattering coefficients are expanded using Debye series (DSE) in order to isolate the contribution of single scattering process. The internal and near-surface electric fields are numerically analyzed, and the effect of beam location, polarization, order of beam, half-cone angle, and scattering process (namely Debye mode p ) are mainly discussed. Numerical results show that a curve formed by extreme peaks can be observed, and the electric fields can be locally enhanced after the interaction of AGVBBs with the particle. Internal and near-surface fields, especially its local enhancement, are very sensitive to the beam parameters, including polarization, order, half-cone angle, etc. The internal fields can also be enhanced by various scattering process (or Debye mode p ). Such results have important applications in various fields, including particle sizing, optical tweezers, etc. [ABSTRACT FROM AUTHOR]

The optical torque exerted on an absorptive megneto-dielectric sphere by an axicon-generated vector Bessel (vortex) beam with selected polarizations is investigated in the framework of the dipole approximation. The total optical torque is expressed as the sum of orbital and spin torques. The axial orbital torque component is calculated from the z -component of the cross-product of the vector position r and the optical force exerted on the sphere F . Depending on the beam characteristics (such as the half-cone angle and polarization type) and the physical properties of the sphere, it is shown here that the axial orbital torque vanishes before reversing sign, indicating a counter-intuitive orbital motion in opposite handedness of the angular momentum carried by the incident waves. Moreover, analytical formulas for the spin torque, which is divided into spin torques induced by electric and magnetic dipoles, are derived. The corresponding components of both the optical spin and orbital torques are numerically calculated, and the effects of polarization, the order of the beam, and half-cone angle are discussed in detail. The left-handed (i.e., negative) optical torque is discussed, and the conditions for generating optical spin and orbital torque sign reversal are numerically investigated. The transverse optical spin torque has a vortex-like character, whose direction depends on the polarization, the half-cone angle, and the order of the beam. Numerical results also show that the vortex direction depends on the radial position of the particle in the transverse plane. This means that a sphere may rotate with different directions when it moves radially. Potential applications are in particle manipulation and rotation, single beam optical tweezers, and other emergent technologies using vector Bessel beams on a small magneto-dielectric (nano) particle. [ABSTRACT FROM AUTHOR]

An analytical description of optical force on a Rayleigh particle by a vector Bessel beam is investigated. Linearly, radially, azimuthally, and circularly polarized Bessel beams are considered. The radial, azimuthal, and axial forces by a vector Bessel beam are numerically simulated. The effect of polarization, order of beams, and half-cone angle to the optical force are mainly discussed. For Bessel beams of larger half-cone angle, the non-paraxiality of beams plays an important role in optical forces. Numerical calculations show that optical forces, especially azimuthal forces, are very sensitive to the polarization of beams. [ABSTRACT FROM AUTHOR]

The interaction of a vector Bessel-Gaussian beam (VBGB) with a dielectric sphere is investigated in the framework of generalized Lorenz–Mie theory (GLMT). The electric field of a VBGB is derived using the angular spectrum decomposition method (ASDM), and the analytical expressions of beam shape coefficients (BSCs) are derived utilizing multipole expansion method using vector spherical harmonics. Various polarizations including linear, circular, radial, and azimuthal polarizations are considered. The far-field scattered intensities are numerically computed, and numerical results show that the beam parameters (including beam-waist radius w 0 , location of beam center, half-cone angle θ b , and polarization type) strongly affect the far-field scattered intensities. The internal and near-surface fields are also calculated, and numerical results show that for smaller θ b two curves formed by extreme peaks can be observed, and for larger θ b such curves disappear and local enhancement of electric fields on the surface can be observed. Such results have important applications in various fields, including particle sizing, optical trapping and manipulation, etc. [ABSTRACT FROM AUTHOR]

• Beam shape coefficients of high-order vector Bessel-Gaussian beams are derived. • Incident beam and scatterer parameters can highly influence the scattering results. • It is not feasible to recognize the relative humidity of aerosol environment by using the differences of scattering intensities. Based on the generalized Lorenz-Mie theory (GLMT) and the angular spectrum decomposition method (ASDM), we derive the beam shape coefficients (BSCs) of high-order vector Bessel Gaussian beams (H-VBGB), and investigate the interaction mechanism of H-VBGB illuminating a spherical marine aerosol. Linear (x, y), circular (left, right), azimuthal and radial polarizations are considered. The effects of various parameters characterizing the incident beam and the aerosol on the normalized differential scattering cross section (DSCS) are investigated. Numerical results show that the normalized DSCS is very sensitive to fluctuations in the parameters, and that the distinctions of incident beams may highly influence results. The relative humidity of aerosol performs similar effects on results for all polarizations, so it is not feasible to recognize the relative humidity of aerosol environment by using the differences of normalized DSCS for various polarization states. We provide a reference for the practical use of the scattering features of non-diffractive beams illuminating spherical calibrators. [ABSTRACT FROM AUTHOR]

• The internal and near-surface fields for a charged sphere by a vector Bessel beam is investigated in the framework of GLMT. • The effects of the surface charge, polarization, order, and half-cone angle are discussed. • The local enhancements of internal and near-surface fields are analyzed. The interaction of an axicon-generated vector Bessel beam (AGVBB) with a charged sphere is investigated in the framework of generalized Lorenz–Mie theory (GLMT). The incident, internal, and scattered fields are expanded using vector spherical wave functions (VSWFs), beam shape coefficients (BSCs), and internal and scattered coefficients. An analytical expressions of beam shape coefficients (BSCs), which are derived using angular spectrum decomposition method (ASDM), are given. The internal and scattered coefficients are derived by considering the boundary conditions. The internal and near-surface electric fields of a charged sphere illuminated by AVGBBs are numerical calculated, and the effects of polarization, order of beam, half-cone angle are mainly discussed. The results are compared with that for neutral particles. The effect of the surface charge are discussed by the comparison of the results for charged spheres with that for neutral particles. Numerical results show that the internal and near-surface fields are sensitive to the surface charge. The internal fields and the near-surface fields can be locally enhanced. Internal and near-surface fields, especially its local enhancement, are very sensitive to the beam parameters, including polarization, order, half-cone angle, etc. [ABSTRACT FROM AUTHOR]