Search

On the basis of generalized Lorenz-Mie theory, the Debye series expansion (DSE) for radiation pressure forces (RPF) exerted on a multilayered sphere induced by focused beams is introduced. The DSE can isolate the contribution of each scattering process to RPF, and give a physical explanation of RPF. Typically, the RPF induced by a Gaussian beam is studied. The DSE is employed to the simulation of RPF corresponding to different scattering processes (diffraction, reflection, refraction, etc.) in detail, and gives the physical mechanism of RPF. The effects of various parameters, such as scattering mode p, beam position, and radius of core for coated spheres, to RPF is researched.

In the framework of Generalized Lorenz–Mie theory (GLMT), based on the expansion results of electromagnetic field radiation components of Bessel pincer light sheets beam acting on dielectric particles of arbitrary size, the expression of radiation force components in a Cartesian coordinate system is obtained by using the Maxwell stress tensor method. On the one hand, the effects of the refractive index and the equivalent radius of spherical particles on the distribution of radiation force are discussed; On the other hand, the influence of beam scaling parameter and beam order of Bessel pincer light sheets beam on the distribution of radiation force are investigated. The results indicate that the changes of particle's refractive index and effective radius only affect the distribution of radiation force. However, the beam scaling parameter and beam order of Bessel pincer light sheets beam have a very sharp impact on the convergence position, distribution range and bending degree far away from the wave source of the radiation force. Single-beam optical tweezers using the self-focusing and self-bending Bessel pincer light-sheets beam are crucial for applications such as single molecule biophysics, optical manipulation and particle separation/clearing. [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 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 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]

The optical radiation force (ORF) and optical spin torque (OST) on an absorptive electromagnetic conductor (AEMC) sphere by an arbitrary-shaped optical polarized beam are investigated in the framework of the generalized Lorenz–Mie theory (GLMT). The analytical expressions of ORF and OST are derived, and both of them are decomposed into three components (co-polarized, cross-polarized, and interference components) due to the unique "optical rotation" effect of the AEMC. The ORF and OST exerted on both a PEMC and an AEMC sphere by an Airy beam are discussed, and the impact of the losses M i of AEMC is focused on. Besides, the influence of particle size parameter k a and admittance parameter M on the ORF and OST are also mainly analyzed. The optical pulling force built on this system is paid attention to and discussed. And the impact of the polarization states of the incident beam on the ORF and OST is also discussed. Furthermore, the comparison of ORF that the Airy beam interacts with a dielectric sphere and an AEMC sphere is studied emphatically. The findings in this manuscript will take effect on particle manipulation, optical spanners, optical tweezers, and metamaterial field. • The optical radiation force and torque exerted on an absorptive electromagnetic conductor (AEMC) sphere by an arbitrary-shaped optic. • The co-polarized, cross-polarized, and interference components of the optical radiation force and torque are studied. • Both the longitudinal and the transversal optical radiation force (including the optical pulling force) and torque are analyzed. • The comparison of ORF that the Airy beam interacts with a dielectric sphere and an AEMC sphere is studied. • The effects from the beam parameters of Airy beam and particle parameters are analyzed. [ABSTRACT FROM AUTHOR]

Abstract: The scattering of an axicon-generated Bessel beam (AGBB) by a sphere is investigated. An analytical formula for the calculation of Beam Shape Coefficients (BSCs) of an AGBB is first derived according to the Integral Localized Approximation (ILA). After the verification of BSCs by the comparison of the reconstructed field using BSCs with the original field obtained from the definition, the far-field scattered intensity is evaluated, and the rainbow produced by AGBB is also studied. The effect of angle on the far-field scattered intensity and the first rainbow is analyzed in detail. Such investigation could provide a useful tool for the research on radiation forces and torques, which is important in optical tweezers and the related optical manipulation applications. [Copyright &y& Elsevier]

• Optical force on a sphere of arbitrary size illuminated by an Airy lightsheet is investigated using GLMT. • The BSCs of the Airy light-sheet are calculated using ASDM and VSWFs. • The negative longitudinal optical force is particularly emphasized. • The two kinds of polarizations (TE and TM) of Airy light-sheet are discussed. • The influences of the transverse scale parameter ω 0 and attenuation parameter γ of the Airy light-sheet are discussed. Based on the generalized Lorenz–Mie theory (GLMT) and the angular spectrum decomposition method (ASDM), we calculate the optical radiation force exerted on a lossless dielectric sphere of arbitrary size illuminated by an Airy light-sheet. The beam shape coefficients (BSCs) of the Airy light-sheet are calculated using the vector angular spectrum decomposition and vector spherical wave functions methods. The optical radiation force acting on the spherical particle is obtained by the integral of Maxwell's stress tensor. The transverse (F y) and longitudinal (F z) forces are numerically computed. Two kinds of polarization (TE and TM) are considered for the Airy light-sheet, and the negative longitudinal optical (pulling) force is particularly emphasized. The influence of the transverse scale parameter w 0 and attenuation parameter γ of the Airy light-sheet on the force is discussed. The results of the present theory are verified using the dipole approximation method in which the gradient force has been also computed for a Rayleigh sphere. The numerical results show that when the transverse scale parameter w 0 and attenuation parameter γ increase, the transverse and longitudinal forces decrease. Furthermore, the force caustic (i.e., maximum) shifts to the direction of y < 0 as the transverse scale parameter w 0 increases. As the dimensionless size parameter of the sphere ka increases (where k is the wavenumber and a is the radius), the resonance peaks of the optical forces become larger. The results of this paper are of practical significance for the development of Airy light-sheet based optical manipulation technologies. [ABSTRACT FROM AUTHOR]

The scattering of x linearly polarized non-diffracting Lommel beam by a perfect electromagnetic conductor (PEMC) sphere is analyzed within the generalized Lorenz–Mie theory (GLMT) framework. The electromagnetic fields of the incident Lommel beams are expressed by employing spherical vector wave functions (SVWFs) and beam shape coefficients (BSCs). These BSCs are mainly considered in the expression of shaped beams in the GLMT with slight beam axicon angle. The scattered electromagnetic fields are constructed using unknown scattering field coefficients (SFCs) and SVWFs. These undetermined SFCs are calculated employing boundary conditions (BCs) at the PEMC surface. The expressions of the far-region/far-zone scattering intensity (FSI) are given and computed. The influences of Lommel beam configuration parameters like as beam order, beam half cone angle, beam asymmetry parameter, beam center coordinates positions, and PEMC sphere size parameter in addition to PEMC scalar admittance on the FSI are analyzed and discussed. The experience of this research work will be quite helpful in analyzing optical radiation force and torque, electromagnetic scattering, light manipulation, antenna engineering domain, optical tweezers, particle interaction, and trapping. Moreover, findings of the study can also be extended to study the interaction between the non-diffracting Lommel beam and the metamaterial structures. [ABSTRACT FROM AUTHOR]

• The optical radiation force and torque exerted on a perfect electromagnetic conductor (PEMC) sphere by an arbitrary-shaped optical polarized beam based on the generalized Lorenz-Mie theory (GLMT). • The co-polarized, cross-polarized, and interference components of the optical radiation force and torque are studied. • Both the longitudinal and the transversal optical radiation force and torque are analyzed and discussed. • The effects from the beam parameters (the order and the hale-cone of the Bessel beam) and particle parameters (the dimensionless size parameter and admittance parameter of the PEMC sphere) are analyzed. Following the previous work [Journal of Quantitative Spectroscopy & Radiative Transfer 281 (2022) 108101], which studied the scattering of an arbitrary-shaped optical polarized beam by a perfect electromagnetic conductor (PEMC) sphere, this paper is devoted to the optical radiation force (OF) and spin torque (OST) exerted on a PEMC sphere by an arbitrary-shaped optical polarized beam based on the generalized Lorenz-Mie theory (GLMT) frame. The analytical expressions of OF and OST on a PEMC sphere are derived according to the multipole expansion method (MEM) and angular spectrum decomposition method (ASDM). The numerical results of the OF and OST and their co-polarized, cross-polarized, and interference components expound on the influence of the particle parameters (admittance parameter M and dimensionless size parameter k a) and the beam parameters (polarization, order l , and half-cone angle α 0). The negative axial OF and the negative axial reverse OST that are sensitive to the α 0 and the polarization states of the Bessel beam are highlighted. Besides, the resonance phenomenon when the high order Bessel beam with a larger α 0 illuminates the PEMC (AEMC) is discussed and analyzed. The absorptive PEMC (AEMC) sphere with losses M i is also paid attention to. And the transversal OF and OST are discussed, emphasizing the vortex characteristics which are sensitive to the M and beam parameters. The above findings have broad application prospects in optical spanners, microparticle manipulation, and optical tweezers. [ABSTRACT FROM AUTHOR]