Research On Electromagnetic Characteristics And Optical Forces Of Chiral Media

Chiral media have been widely studied and applied in microwave and optics fields because of their special physical characteristics.The interaction between electromagnetic wave and chiral media is currently a hot topic.The electromagnetic scattering and the optical force of chiral media based on the electromagnetic field theory are studied in this thesis.The electromagnetic wave propagation and scattering,radiation pressure,as well as gain properties of chiral media are theoretically studied with the Mie series solution,the finite-difference time-domain(FDTD)method and the propagation matrix method(PMM)in the thesis.The applications of chiral media in cloak and optical micromanipulation are discussed.The main contents in the thesis are as follows:Firstly,the electromagnetic scattering of single chiral metamaterials(CMMs)sphere is researched.Meanwhile the electromagnetic scattering of two-layer sphere,that is,a conducting sphere coated with chiral metamaterials,based on Mie series solution is simulated.Mie series solution formulas for radar cross section(RCS)electromagnetic scattering of one-layer and two-layer spheres containing dispersive homogeneous chiral metamaterials are derived and realized.The effects of epsilon-negative or mur-negative,epsilon-negative and mur-negative,as well as chirality parameters etc of the coated chiral metamaterials to the co-polarized and cross-polarized scattering of the metallic sphere are compared.The results of the Mie series solution illustrate that(i),with increasing the refractive index,more surface modes resulting from the resonances contribute to scattering.Due to the negative refractive characteristic of CMMs,the forward RCS of a chiral metamaterials are stronger than that of a metallic sphere with the same size,the backward RCS is reverse.(ii),the existence of chirality parameter of a conducting sphere coated with CMMs in generally decreases the RCS at large angles compared to normal media coating layer with the same size.This implies that the chiral metamaterials may be a promising electromagnetic absorber material.Secondly,based on the auxiliary differential equation(ADE)-FDTD method,the distribution of electromagnetic fields and Lorentz force densities in dispersive gain chiral slab and column are simulated as the plane wave is incident.First,starting from constitutive relations and introducing magnetic dispersion and chirality parameter,the auxiliary differential equation(ADE)method in finite-difference time-domain method for the computation of electromagnetic characteristics of chiral media are derived.The Drude,Lorentz and Condon models are used to simulate chiral media.The relationships between electromagnetic polarization densities and induced and coupled electromagnetic polarization densities of dispersive chiral media are presented.Secondly,the Lorentz force density for chiral media containing bound electric charge and electric current densities,as well as bound magnetic charge and magnetic current densities is derived.The differential equations describing the characteristics of electromagnetic wave in chiral media are given.The three-dimensional,two-dimensional and one-dimensional ADE-FDTD formulas for chiral media by discretizing these equations are obtained.Compared with the literature results,the correctness of the ADE-FDTD method and the Lorentz force density method are verified.Finally,the distribution of fields and optical forces for an active chiral cylinder is simulated.The contribution of electromagnetic current and electromagnetic charge densities to the Lorentz force density is discussed.The numerical results show that(i),the cross-polarized transmission coefficient is larger than the co-polarized transmission coefficient for a gain chiral slab with certain thickness.The pressure gradient force resulting from bound currents of the cross-polarized wave in chiral media is larger than the scattering force,thus inducing the slab towards the incident source.The complicated optical pulling or pushing force density among slabs including chiral medium with different media parameters illuminated by a normally incident plane wave is discussed.(ii)A focusing point source is produced by the coupled cross-polarized waves to capture the dispersive gain chiral cylinder with Im2(?)>|Im(?)Im(?)|/(?0?0)as the plane wave is incident.The pulling force is attributed to the magneto-electric coupling characteristics induced by the chirality parameter and the cross-polarized electromagnetic currents' contribution.(iii),the capture of the common dielectric cylinder coated by the active chiral medium is mainly contributed by the cross-polarized bound currents in the chiral medium.However,their contribution to the Lorentz force density in the inner dielectric layer can be neglected.The work in this section may provide some theoretical guidance for chiral media's potential engineering applications in optical tweezers and the measurement of the chiral parameter.Finally,the electromagnetic scattering and optical force on an inhomogeneous media slab containing active isotropic chiral media are computed with the propagation matrix method(PMM).Based on the Maxwell equations and constitutive relations of chiral media,the electromagnetic wave in chiral media is decomposed into uncouping eigen modes.The analytical propagation matrix method,which can compute the co-and cross-polarized reflection and transmission coefficients for multilayer chiral medium slab,is derived according to the electromagnetic boundary conditions.The optical force density for the chiral media slab is derived based on the Maxwell stress tensor.The validation of the method is performed by comparing the references' results.Finally,the co-and cross-polarized reflection and transmission coefficients and optical force densities for chiral slab are simply calculated.