Tan Qu

Analysis of the radiation force and torque exerted on a chiral sphere by a Gaussian beam

Under the framework of generalized Lorenz-Mie theory, we calculate the radiation force and torque exerted on a chiral sphere by a Gaussian beam. The theory and codes for axial radiation force are verified when the chiral sphere degenerates into an isotropic sphere. We discuss the influence of a chirality parameter on the radiation force and torque. Linearly and circularly polarized incident Gaussian beams are considered, and the corresponding radiation forces and torques are compared and analyzed. The polarization of the incident beam considerably influences radiation force of a chiral sphere. In trapping a chiral sphere, therefore, the polarization of incident beams should be chosen in accordance with the chirality. Unlike polarization, variation of chirality slightly affects radiation torque, except when the imaginary part of the chirality parameter is considered.

Electromagnetic scattering by a uniaxial anisotropic sphere located in an off-axis Bessel beam

Electromagnetic scattering of a zero-order Bessel beam by an anisotropic spherical particle in the off-axis configuration is investigated. Based on the spherical vector wave functions, the expansion expression of the zero-order Bessel beam is derived, and its convergence is numerically discussed in detail. Utilizing the tangential continuity of the electromagnetic fields, the expressions of scattering coefficients are given. The effects of the conical angle of the wave vector components of the zero-order Bessel beam, the ratio of the radius of the sphere to the central spot radius of the zero-order Bessel beam, the shift of the beam waist center position along both the x and y axes, the permittivity and permeability tensor elements, and the loss of the sphere on the radar cross section (RCS) are numerically analyzed. It is revealed that the maximum RCS appears in the conical direction or neighboring direction when the sphere is illuminated by a zero-order Bessel beam. Furthermore, the RCS will decrease and the symmetry is broken with the shift of the beam waist center.

Analysis of rainbow scattering by a chiral sphere

Based on the scattering theory of a chiral sphere, rainbow phenomenon of a chiral sphere is numerically analyzed in this paper. For chiral spheres illuminated by a linearly polarized wave, there are three first-order rainbows, with whose rainbow angles varying with the chirality parameter. The spectrum of each rainbow structure is presented and the ripple frequencies are found associated with the size and refractive indices of the chiral sphere. Only two rainbow structures remain when the chiral sphere is illuminated by a circularly polarized plane wave. Finally, the rainbows of chiral spheres with slight chirality parameters are found appearing alternately in E-plane and H-plane with the variation of the chirality.

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.

General theory on electromagnetic scattering of an off-axis Hermite-Gaussian beam by a rotationally uniaxial anisotropic spheroid

This letter presents a field expansion of the solution to three-dimensional electromagnetic scattering problems of a uniaxial anisotropic spheroidal particle illuminated by an off-axis Hermite-Gaussian (HG) beam. Using the complex-source-point method, and the relationship between spherical and spheroidal vector wave functions (VWFs), a method is put forward to expand the incident Hermite-Gaussian beam in terms of the spheroidal VWFs. By utilizing the complete relationship between spherical and spheroidal VWFs, the expansion formats of the EM fields in a uniaxial anisotropic spheroid in terms of the spheroidal vector wave functions are derived. The unknown expansion coefficients of the internal fields and scattered field are determined by applying the boundary conditions of the continuity of the tangential components of the electric and magnetic vectors across the surface of the spheroid. These theory works are hopeful to provide an effective test for further research on the numerical analysis of the interaction between a uniaxial anisotropic spheroid and laser beam.

Scattering of a uniaxial anisotropic sphere incident by a Laguerre-Gaussian vortex beam

The analytical theory for the scattering of a uniaxial anisotropic illuminated by a Laguerre-Gaussian vortex beam is presented. Based on the complex source point method and the relation between Hermite polynomial and Laguerre polynomial, the expansion of Laguerre-Gaussian vortex beam expanded in terms of spherical vector wave functions is derived. Using the continuous boundary condition at the surface of the sphere, the scattering coefficients are obtained. The scattering intensity distributions of a uniaxial anisotropic sphere incident by a Laguerre-Gaussian vortex beam are numerically analyzed in detail.

Generation of OAM waves using metamaterials substrate antenna

In this paper, we demonstrate a single layer X-band (8-12 GHz) metamaterials substrate antenna for generating orbital angular momentum (OAM) beam. The proposed design consists of a series of phase-shift unit cells to control the emergent phase, whose function is same as spiral phase plate (SPP). The SPP uses the concept of reflectarray antenna having a double circular ring type unit cell to control the reflection phase for generating beams carrying OAM wave. The results of phase patterns simulation verify that the vortex radio waves can be generated by using sub-wavelength reflective metamaterials substrate antenna. From the perspective of the electromagnetic calculation, we can use high performance computing to reduce the computation time.

Scattering Properties of the Higher-Order Hermite Gaussian Beam

Based on the derivatives between the fundamental and higher-order Hermite Gaussian beam and the Davis’s one-order approximation of slowly varying function, a general expression of the higher-order Hermite Gaussian beam are presented. Scattering characteristics of higher-order off-axis Hermite Gaussian is investigated. Some selected calculations on the effects of the beam waist width and the beam waist center positioning are described.