Propagation And Scattering Theories Based On The Two-dimensional Material Plasmons

Plasmon is a kind of surface wave,which is formed by the coupling between the electromag-netic wave and the free electrons on the metal surface,and propagates along the metal-dielectric surface.Due to the peculiar optical properties of metallic nanostructures,plasmons can steer light in the subwavelength scale.Based on the plasmons,people are expected to design the high-speed,miniaturized and integrated plasmonic chips,which may be used in the next generation information technology.This thesis will give a brief introduction to the plasmons first,which mainly focuses on the three typical concepts including Airy plasmons,superscattering and nonlinear plasmons.For the Airy plasmons,the conventional plasmonic modes usually have no tunability,which leads to the non dynamical steerability of the propagation trajectories of Airy plasmons.For the superscatter-ing,the conventional plasmonic modes have weak confinements,which hinders the enhancements of the scattering cross sections of deep-sub wavelength objects.For the nonlinear plasmons,due to the small nonlinear susceptibilities of the dielectrics,the conventional nonlinear plasmonic devices based on the nonlinear dielectrics usually require high input powers.In order to deal with the three scientific problems including the non dynamical steerability of the Airy plasmons,the difficulties in the design of deep-subwavelength superscatterers and the high input powers of the nonlinear plasmonic devices,a new kind of two dimensional material,graphene,is introduced in this thesis.On the one hand,by employing the linear and(or)nonlinear surface conductivities of graphene,linear propagation theory,nonlinear propagation theory,linear scattering theory and nonlinear scattering theory based on the graphene plasmons are developed to extend or modify the propagation and scattering theories based on the conventional plasmons.On the other hand,considering some typical and analytically solvable electromagnetic structures,some ideas are provided to the above three scientific problems by using the peculiar properties of graphene plasmons.The main content includes the following several aspects:1.The development of the linear propagation theory based on the graphene plasmons.First this thesis studies the hybrid modes in a planar hybrid plasmonic waveguide by using the linear propagation model.Then considering the non dynamical steerability of Airy plasmons,it illustrates the hybrid Airy plasmons with dynamically steerable trajectories.2.The development of the nonlinear propagation theory based on the graphene plasmons.By using the nonlinear propagation model and considering the high input powers of the nonlinear plasmonic devices,this thesis studies the plasmonic modes and dispersion relations in a cylindrical nonlinear graphene plasmonic waveguide under low input powers.3.The development of the linear scattering theory based on the graphene plasmons.First considering the difficulties in the design of deep-subwavelength superscatterers,by taking a two dimensional cylindrical structure as an example,this thesis proposes a method to realize the deep-subwavelength superscattering by using the graphene plasmon resonance.Then it extends the graphene plasmon resonance into the three dimensional spherical structure.Finally,it further im-proves the performances of the superscatterers based on the principle of resonance overlapping,and analyzes the factor that restricts the performance improvement.4.The development of the nonlinear scattering theory based on the graphene plasmons.By using the nonlinear scattering model and considering the high input powers of the nonlinear plas-monic devices,this thesis studies the bistable scattering behavior under low input intensities.Be-sides,it discoveries that the switching thresholds of bistable scattering are restricted by the relax-ation time of carriers in graphene.