| Charged bodies widely exist in a plasma environment and an electrolyte environment.Exchanging electrons or ions with these environment,charged bodies own some quantities of excess electric charge.Excess charge is an important parameter since it controls the coupling to other particles and to external electromagnetic fields as well as the overall charge balance of the environment.Therefore,electromagnetic scattering of the charged particles is an important problem.Assuming the charges located at the surface of charged bodies,researchers employ the phenomenological surface conductivity induced by the excess charges in electromagnetic boundary conditions,to solve the scattering of the charged bodies.Yet,two problems among the researches remain a challenge.First,on the shape of the bodies,studies about the non-spherical charged bodies still lack in literature.Second,on the host medium,the dependence of scattering properties on the absorbing host medium has not been investigated systematically.However,at some wavelengths,both the plasma and the electrolyte are absorbing media.To solve these two problems,this thesis aims to study electromagnetic scattering of a charged planar interface,a charged sphere,and a charged cylinder and consider the effects of the absorbing host media on the scattering properties.In this thesis,the Maxwell equations and general boundary conditions including the surface conductivities are used.The specific research contents are as follows:For a planar interface,reflection and refraction at the interface between two infinite media are basic problems in electromagnetics,which are used to solve the light properties of the multilayered films.Yet,electromagnetic scattering at a charged planar interface remains a challenge.As a result,this thesis aims to study gererally electrogagnetic scattering theory suitable for the charged planar interfaces between two infinite absorbing media.In absorbing media,the plane waves are harmonic inhomogeneous plane wave(HIPW),which own different directions of phase propagation vector and amplitude propagation vector,i.e.the surfaces of equal amplitudes are different with those of equal phase.When the propagation direction of phase coincides with that of amplitude,HIPW reduces to the harmonic homogeneous plane waves(HHPW).The generalized laws of Snell,Fresnel and energy balance are derived for the harmonic inhomogeneous plane waves(HIPW)that are incident upon a charged plane interface between two absorbing media.No significant charge effects are found for the generalized Snell laws.The surface conductivity is included in the generalized Fresnel laws.Besides usual reflection and refraction,the interference induced by the absorbing media and Joule heat loss caused by the excess surface charges must be considered in the relations of energy balance.The reflection and transmission coefficients are calculated by the equations,and the validity of the results is verified by comparison with those calculated by the finite-difference timedomain method.In addition,this thesis identifies a charge-induced increase of(pseudo)Brewster angle for the harmonic homogeneous plane waves(HHPW),a significant influence of the incident angles for amplitude propagation vector on optical properties for HIPW,and a strong increase of Joule heat loss due to the interaction between the incident HIPW and the surface charges.An absorbing host medium and surface conductivity of a charged sphere are two emerging factors that influence electromagnetic scattering and play a role in tuning optical properties of the sphere.In this thesis,a general case of the light scattering by a charged sphere embedded in an absorbing host medium is considered.Combining the two established Lorentz-Mie theories which apply to the absorbing host medium and the charged sphere,this thesis calculates the far-field extinction efficiency factor and the nearfield electric field amplitude.The results show that amplifying effect of the increasing absorption of host medium on the interference oscillations of the extinction efficiency factor is opposite to the damping effect of the increasing surface conductivity.On the electric field amplitude,the increasing absorption of the host medium enhances the backscattering field in contrast to the front-scattering field.However,the increasing surface conductivity induces a size-parameter dependent change on the pattern of the field distribution and the magnitude of the field.The results indicate that the far-and near-field optical properties of spheres can be regulated and controled by the absorbing host medium and the excess charges.Although charged particles exist widely in a plasma environment or an electrolyte,the problem of electromagnetic scattering by a charged cylinder has remained unsolved.The optical properties for a sphere are independent of the state of polarization of the incident light due to the symmetry of the sphere.This is still true for a uniformly charged sphere,since the excess surface charges do not break the symmetry.However,the optical cross sections for a non-charged cylinder can be quite different for different polarizations.Therefore,for a charged cylinder,the effects of the excess surface charges on the optical cross sections may be largely different for the incident p-and s-polarized lights.In this thesis,using the tangential boundary conditions with a surface current induced by excess surface charges,the extinction,scattering,and absorption efficiencies togheher with the near-field electric field for a charged infinite cylinder upon which a plane wave is normally incident are calculated.For two polarizations of the incident light,the different effects of the excess surface charges on the optical efficiencies are shown.For ppolarization,the extinction efficiencies own a platform structure where the extinction is in proportion to the density of surface charges,which corresponds to the light absorption by the excess surface charges.For s-polarization,the excess surface charges will induce a new resonance at the dielectric function of the cylinder larger than-1 and a shift on the anomalous resonance which can only exist for the dielectric function near and smaller than-1.The increasing surface charge density can shift these resonances to a larger size parameter and broaden the widths of the anomalous resonances.Furthermore,considering a specific case of a charged Mg O cylinder,we identify a blue shift of the resonances near the longitudinal optical phonon frequency.For the near-field electric field,the effects of excess charges on the electric field can be devided into two different regions.In the surface-charge-resonance region,the excess surface charges induce a field transfer from interior to exterior of the cylinder.In the anomalous resonance region,surface charges can produce a field transfer from the exterior of the cylinder to the interior.Gold nanoparticles can be widely applied in bio-optics and nanophotonics.Gold nanoparticles are ofter charged in the preparation process.As a result,this thesis calculates the optical properties of charged planes,spheres,and cylinders.For planes,the Joule heat induced by the surface conductivity reachs maximum at the surface plasmon resonance wavelength.For spheres,the resonances in extinction efficiency are red shifted by the increasing surface conductivity.For cylinders,the resonances in extinction efficiency are broaden to the larger wavelength by the increasing surface conductivity.To calculate the optical properties of charged gold particles,this thesis measures the dielectric function of three different gold films using two ellipsometers covering the spectral range from 200 nm to 25 ?m.Based on the Drude model and the MayadasShatzkes model of the electron-grain boundary scattering,this thesis find that electronic reflection coefficient at the grain boundary is a vital factor to influence the dielectric function of the polycrystalline gold films.Yet,a large variation exists in the measured optical dielectric function of gold between different sources,which further induces a large variation of light properties of the particles.The results suggest that,in addition to grain size and surface roughness,the difference of electron reflection coefficient at the grain boundary also contributes to the large discrepancies of the measured dielectric function in the past 60 years. |
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