Manipulation Of The Resonance Modes Of Nanostructures By Vector Beams

It reveals many new physical phenomena and drives a variety of related new applications in photonic integrated devices,high-performance data processing,optical computing,super-resolution imaging,enhanced spectroscopy and biochemical sensing,when study the linear and nonlinear light-matter interaction at the nanoscale beyond the optical diffraction limit.This has greatly promoted the development of modern optics,and the resulting emerging field of nanophotonics.Many applications of nanophotonics commonly rely on the electric near-field and far-field scattering characteristics of plasmonic or dielectric nanostructure elements at their resonance modes,making the research on manipulation of resonance characteristics of nanostructures and their resonance modes become the basis of nanophotonics.It is also crucial for understanding the mechanism of related physical phenomena and improving the optical response of nanostructures.Typically,researchers manipulate the resonance modes of nanostructures by modifying their size,shape and composition,while ignoring the regulation of specific illumination light fields.In recent years,with the deepening of the research on vector beams with spatially uneven polarization distributions,the interaction between vector beams and nanostructures has also attracted extensive research interest.Due to the matching between the special electromagnetic field intensity,phase and polarization distributions of the focused vector beams and the nanostructures’ resonance modes,the vector beams can efficiently and selectively excite the specific resonance modes of the nanostructures and effectively manipulate the electric near-field and far-field scattering field,which has important guiding significance for the basic research and practical application of nanophotonics.In this thesis,manipulations of resonance modes of different nanostructures by focused radially polarized beam(RPB)and azimuthally polarized beam(APB)illuminations are systematically studied in theory,experiment and numerical simulation.The main research contents and research results are as follows:(1)Experimental and numerical simulation studies of the selective excitation of the transverse electric dipole(TD)and vertical electric dipole(VD)resonance modes in an individual gold nanosphere by employing focused RPB and APB illuminations.The focused APB has a purely azimuthally polarized electric field distribution in the focal plane,which can only excite the TD resonance mode with an arbitrary in-plane orientation in the gold nanosphere by moving the nanosphere within the focal plane.Moreover,the focused RPB has a unique three-dimensional electric field polarization distribution in the focal plane,which can selectively excite both the TD and VD resonance modes in the gold nanosphere.These two induced resonance modes finally superimpose to obtain an electric dipole resonance mode with an arbitrary three-dimensional orientation and effectively tailor the electric near-field distribution of the gold nanosphere.(2)Theoretical and numerical simulation studies of the selective excitation of the TD resonance mode and vertical magnetic dipole resonance mode in a single metal-dielectric core-shell nanosphere under the focused APB illumination.The focused APB has both azimuthally polarized electric field component and longitudinally polarized magnetic field component in the focal plane,which can selectively excite the TD resonance mode and vertical magnetic dipole resonance mode with different intensities in the core-shell nanosphere as the nanosphere moves away from the optical axis.These two resonance modes superimpose in the far-field to produce an effectively controlled scattering distribution with different transverse unidirectionality.(3)Numerical simulation studies of the effective and selective excitation of the localized surface plasmon resonance modes,especially the dark plasmon modes,in an individual metallic nanostructure under a focused RPB illumination.The three-dimensional electric field polarization with different local symmetric distributions within the RPB focal plane can effectively and selectively excite the VD and TD plasmon resonance modes,as well as the even-order and odd-order longitudinal plasmon resonance modes in an individual gold nanorod.Similarly,the focused RPB can also effectively and selectively excite the radial breathing dark plasmon mode,electric dipole and quadrupole plasmon modes with different electric dipole moment distributions in an individual silver nanodisk.(4)Numerical simulation studies of the effective excitation of the plasmonic Fano resonance in a gold split-ring resonator(SRR)-nanoarc structure under a focused APB illumination.As compared to the linearly polarized beam(LPB)illumination,the electric field polarization and intensity distributions of a focused APB can efficiently match and effectively excite the plasmonic bonding mode of the SRR-nanoarc structure,which makes the Fano lineshape much more asymmetric and the near-field intensity enhancement become more than60 times larger.Moreover,the near-field intensity enhancement of the gold SRR-nanoarc structure under an APB illumination can effectively improve the efficiency of the second harmonic generation(SHG)and an almost 30 times increase in SHG intensity at the plasmonic bonding mode can be achieved as compared to the counterpart excited by an LPB.In the far-field domain,the APB can excite a much more symmetric SHG radiation pattern than that excited by an LPB.