Scattering Of Chiral Sphere And Chiral Cylinder By Plane Waves And Gaussian Beams

Chiral medium has been researched a lot and been widely used in both microwave region and optics region due to its special property. One important research area is the interaction of electromagnetic wave with chiral particles. This thesis researches detailedly on scattering of chiral sphere and infinite long chiral cylinder based on electromagnetic theory. The specific problems are as follows:reflection and transmission of multilayered chiral slabs, scattering from chiral sphere, scattering from multilayered chiral sphere, radiation pressure and torque exerted on chiral sphere, and scattering from infinite long chiral cylinder. Each aspect of the research work in this thesis is summarized below.1. Based on constitutive relations of chiral medium and Maxwell equations, electromagnetic wave in a chiral medium can be decomposed into right circularly polarized wave and left circularly polarized wave. According to the boundary conditions, reflection and transmission of waves at chiral-achiral interface and achiral-chiral interface can be determined. Iterative analytical solutions of reflection and transmission of multilayered chiral slabs are proposed. Reflection and transmission characteristics from achiral-chiral interface, chiral-achiral interface and multilayered chiral slabs are analyzed numerically.2. Rayleigh model and analytical theory for scattering of a chiral sphere are researched. By regarding the scattering of a small chiral sphere as radiation problem of dipoles, equivalent dipole moments of a chiral sphere are obtained and accordingly scattering of a Rayleigh chiral sphere is calculated. The analytical theory is developed in Lorenz-Mie frame. The incident wave, internal field and scattered field of the chiral sphere are expanded in terms of spherical vector wave functions. According to the boundary conditions, expressions of expansion coefficients of internal field and scattered field can be obtained. As the expressions are written in forms of logarithmic derivatives and ratios of Riccati-Bessel functions, a stable and convergent algorithm is constructed which solves the calculation for scattering of large sized chiral sphere. Properties of scattered fields in the far field are analyzed based on the numerical results. It is found that a large sized chiral sphere with proper chirality has three first-order rainbows; and two of them are corresponding to two equivalent refractive indices of the chiral sphere. The three rainbows can be explained by using geometric optics and rainbow angles are calculated accordingly. Chirality parameter and size of a chiral sphere can be inverted by using relations between rainbow structure and parameters of a large sized chiral sphere.3. Analytical solutions to scattering from multilayered chiral sphere are studied in Lorenz-Mie regime. Electromagnetic fields in each region of the multilayered chiral sphere are expanded in terms of spherical vector wave functions. By using the boundary conditions at each layer, the relations between field expansion coefficients in adjacent regions can be determined. Accordingly an iteration is constructed and recurrence relations for calculating expansion coefficients in each region are solved. Iterative solutions overcome difficulties of calculation compared with matrix methods and are applicable to case of large sized multilayered chiral sphere. Scattered field and internal fields in each region of multilayered chiral sphere illuminated by plane waves and Gaussian beams are numerically calculated and analyzed. Angular distributions of RCSs oscillate strongly as size of the multilayered chiral sphere increases; and rainbow scattering patterns also occur for large sized case. For linearly polarized waves incidence, right and left circularly polarized components of the internal fields and near fields are not consistent.4. According to the momentum theorem of electromagnetic field and the analytical scattering theory of a chiral sphere, radiation pressure and torque exerted on a chiral sphere can be determined by expansion coefficients of incident beam and scattered fields. Radiation pressure and torque exerted on a chiral sphere and a multilayered chiral sphere by a Gaussian beam are analyzed. According to the numerical results, the polarization of the incident beam considerably influences radiation force of a chiral sphere. And choosing an appropriately polarized beam will make the trapping easier. The thickness of the outer layer of a multilayered chiral sphere has a considerably effect on axis radiation pressure, and has a weak effect on the transverse radiation force. Variation of chirality minimally changes radiation torque unless the chiral parameter is complex value. And the radiation torque exerted on a chiral sphere by a Gaussian beam depends on two factors:absorption of the sphere, and the polarization of the incident beam.5. Scattering from an infinite chiral cylinder is researched under frame of Lorenz-Mie theory. Analytical solutions to scattering from an infinite chiral cylinder at oblique incidence are presented. The scattering coefficients are expressed in forms of ratios and logarithmic derivatives of cylindrical Bessel functions, which overcome difficulties of calculation for large sized case. Effects of the cylinder parameters such as chirality, loss and incident angle on scattering properties are numerically analyzed. A large sized chiral cylinder with proper chirality also has three first-order rainbows. And the rainbow angle varies vesus incident angle.