Non-Rayleigh scattering behavior for anisotropic Rayleigh particles

Light scattering of a uniform uniaxial anisotropic sphere by an on-axis high-order Bessel vortex beam

Analytical solutions to the scattering of a uniform uniaxial anisotropic sphere illuminated by an on-axis high-order Bessel vortex beam (HOBVB) are investigated. Using the vector wave theory, the expansion coefficients of the incident HOBVB in terms of the spherical vector wave functions (SVWFs) are obtained. According to the orthogonality of the associated Legendre function and exponential function, more concise expressions of the expansion coefficients are derived. It can reinterpret the incident HOBVB faster compared with the expansion coefficients of double integral forms. The internal fields of a uniform uniaxial anisotropic sphere are proposed in the integrating form of the SVWFs by introducing the Fourier transform. The differences of scattering characteristics of a uniaxial anisotropic sphere illuminated by a zero-order Bessel beam, Gaussian beam, and HOBVB are exhibited. Influences of the topological charge, conical angle, and particle size parameters on the angle distributions of the radar cross section are analyzed in detail. The scattering and extinction efficiencies varied with the particle radius, conical angle, permeability, and dielectric anisotropy are also discussed. The results provide insights into the scattering and light-matter interactions and may find important applications in optical propagation and optical micromanipulation of biological and anisotropic complex particles.

Analysis of radiation force on a uniaxial anisotropic sphere by dual counter-propagating Gaussian beams

Based on Maxwell's stress tensor and the generalized Lorenz-Mie theory, a theoretical approach is introduced to study the radiation force exerted on a uniaxial anisotropic sphere illuminated by dual counter-propagating (CP) Gaussian beams. The beams propagate with arbitrary direction and are expanded in terms of the spherical vector wave functions (SVWFs) in a particle coordinate system using the coordinate rotation theorem of the SVWFs. The total expansion coefficients of the incident fields are derived by superposition of the vector fields. Using Maxwell stress tensor analysis, the analytical expressions of the radiation force on a homogeneous absorbing uniaxial anisotropic sphere are obtained. The accuracy of the theory is verified by comparing the radiation forces of the anisotropic sphere reduced to the special cases of an isotropic sphere. In order to study the equilibrium state, the effects of beam parameters, particle size parameters, and anisotropy parameters on the radiation force are discussed in detail. Compared with the isotropic particle, the equilibrium status is sensitive to the anisotropic parameters. Moreover, the properties of optical force on a uniaxial anisotropic sphere in a single Gaussian beam trap and Gaussian standing wave trap are compared. It indicates that the CP Gaussian beam trap may more easily capture or confine the anisotropic particle. However, the radiation force exerted on an anisotropic sphere exhibits very different properties when the beams do not propagate along the primary optical axis. The influence of the anisotropic parameter on the radiation force by CP Gaussian beams is different from that of a single Gaussian beam. In summary, even for anisotropic particles, the Gaussian standing wave trap also exhibits significant advantages when compared with the single Gaussian beam trap. The theoretical predictions of radiation forces exerted on a uniaxial anisotropic sphere by dual Gaussian beams provide effective ways to achieve the improvement of optical tweezers as well as the capture, suspension, and high-precision delivery of anisotropic particles.

Realizing optical bistability and tristability in plasmonic coated nanoparticles with radial-anisotropy and Kerr-nonlinearity

We theoretically study the optical bistability and tristability in plasmonic coated nanospheres containing the nonlinear plasmonic shell and the dielectric core with radial anisotropy. Based on self-consistent mean-field approximation, we establish the relationship between the local field in the shell and the applied incident field, taking into account the Lorentz local field. One or two optical bistabilities and even optical tristability can be observed. Especially, there are two critical geometric parameters between which two optical bistabilities exist. Physically, two optical bistablities result from the excitations of two surface plasmonic resonant modes in the inner and outer interfaces of coated nanospheres, which are well reflected from the spectral representation with two poles. Moreover, the involvement of the radial anisotropy is quite essential to realize the optical tristability. Further discussion on the field-induced tuning of the reflectance reveals the macroscopic properties of this nonlinear optical structure, which provides a potential candidate for designing multi-stable optical devices at the nanoscale.

Near-field radiative transfer between magneto-dielectric uniaxial anisotropic media

We investigate the near-field radiative heat transfer between two semi-infinite magneto-dielectric uniaxial anisotropic media (MDUAM). SiC nanowires embedded in metamaterials are used to implement electric and magnetic anisotropy, which leads to the hyperbolic dispersion relation for both TE and TM waves. The results show that the TM and TE waves can support both hyperbolic modes and surface modes and that there exist additional modes contributing to the heat transfer for TE waves. Moreover, the MDUAM exhibit super-Planckian thermal emission at ultra-broad bandwidths. This work paves the way for applying the near-field radiative heat transfer in the area of thermal management and energy harvesting.

Anomalous optical forces on the anisotropic Rayleigh particles

We investigate the optical forces on the radially anisotropic spheres from an incident plane wave based on our generalized full-wave scattering theory and the Maxwell stress tensor integration techniques. We demonstrate that the optical force on the Rayleigh sphere with radial anisotropy does not always obey the well-known Rayleigh's law F~k04a(6) (where k(0) is the wave number and a is the radius of the sphere), but could be anomalous with the laws such as F~k00a(2), F~k0-2a(0), and F~k08a(10) under certain conditions. Therefore, the optical force on the anisotropic Rayleigh spheres is enhanced at the electric dipole resonance, and may be further increased by tuning the anisotropic parameters. On the contrary, the optical forces on the anisotropic spheres can be largely reduced for anisotropic spheres with electromagnetic transparency.

Controlling light scattering and polarization by spherical particles with radial anisotropy

Based on full-wave electromagnetic theory, we derive the zero-forward and zero-backward scattering conditions for radially anisotropic spheres within the quasi-static limit. We find that the near-field intensity can be tuned dramatically through the adjustment of the radial anisotropy, while the far-field light scattering diagrams are similar under the zero-forward or zero-backward scattering conditions. Generalized "Brewster's angle" for anisotropic spheres is also derived, at which the scattering light is totally polarized. In addition, the high-quality polarized scattering wave and the tunable polarization conversion can be achieved for the radially anisotropic spheres.