Anomalous Electromagnetic Transport And Nonlinear Effects In Nanoparticle Systems

The interaction between electromagnetic wave and nanoparticle has potential applications,such as light cloaking,optical communication system and device,super sensitive military detection,and so on.In this thesis,full-wave electromagnetic scattering theory is developed to study the optical scattering and optical force on radially anisotropic nanowires.In addition,because of the rapid development of coated nanoparticles,we study Fano resonance on radially anisotropic coated nanowires.The large enhancement of the local fields at the resonance wavelength is quite useful for realizing the nonlinear optical effect.In the strong-nonlinear case,we resort to the mean-field approximation to study the tunable optical bistability.And then further study the premise condition for the coated nonlinear nanoparticles.The main results are listed as follows.1.Anomalous optical behavior for radially anisotropic nanowiresFull-wave electromagnetic(EM)scattering theory is provided to discuss the electromagnetic scattering efficiency of radially anisotropic nanowires.In the longwavelength limit,we derive the conditions for observing unusual EM scattering including non-Rayleigh vanishing and diverging ones.The anisotropic nanowires under certain conditions can be hardly visible or exhibit superscattering.In addition,Maxwell stress tensor integration technique is adopted to study the optical force.Decreasing the incident wave vector,the optical forces on the anisotropic nanowires under non-Rayleigh vanishing is rapidly weaken,while,under the diverging case,the optical force is enhanced.2.Unconventional Fano resonances in coated nanowires with radial anisotropyFurther study the electromagnetic scattering of radially anisotropic coated nanowires.For coated nanowires containing radially anisotropic core and plasmonic shell,unconventional Fano resonances are predicted due to the interference between dipole cloaking mode and dipole resonant mode.In contrast to Z-shaped Fano profile with small modulation depth for coated nanospheres,S-shaped Fano profile for coated nanowires exhibits high depth.Furthermore,increasing the inner size and the radial permittivity elements of the anisotropic core,Fano-like profiles for the nanowires red shift.3.Optical properties in composite media containing spherical particles with different sizesWe study the effective nonlinear optical properties of composite media in which identical nonlinear nanospheres are randomly embedded in the linear host medium.In the weakly-nonlinear case,combining effective medium theory with the linear Lorenz-Mie scattering theory to study the effective linear permittivity and effective third-order nonlinear susceptibility.Large enhancement of optical nonlinear susceptibility can be achieved at the surface plasmon resonant wavelength,which can be enhanced by decreasing the size of nanoparticles.In the strong-nonlinear case,based on self-consistent mean field approximation,nonlinear Lorenz-Mie scattering theory is developed to study the optical bistability.For the smaller nanoparticles,decreasing the size of the nanoparticle or the permittivity of the surrounding media,the region of the optical bistability become broaden.And for the larger nanoparticles,optical tristability are found due to the effects of the high modes.4.Optical bistability in a nonlinear shell-coated metallic nanoparticleBased on self-consistent mean field approximation and Lorenz-Mie scattering theory to study the optical property of a metallic nanoparticle coated with a nonlinear shell.The coated nanoparticle exhibits optical bistability in strong incident optical intensity.This optical bistability critically relies on the geometry of coated shell,especially the volume fraction of the metallic core.Considering the nanoparticle in low permittivity medium,the volume fraction of the metallic core must be larger than the critical value to obtain optical bistability.While for the high permittivity,the volume fraction should be smaller than the critical value.What's more,through an optimization-like process,we find a design with broader bistable region by decreasing the size of the nonlinear nanoparticle or increasing the incident wavelength.