Research On Near Filed Enhancement And Far Filed Characteristics Of Nanoantennans

As one of the hot research fields of micro-nano photonics,the application of optical nanoantennas in photoelectric detection,biosensors,surface-enhanced Raman scattering,and near-field microscopy has great value and great development potential.The electromagnetic field multipole resonance of optical nano-antennas will affect each other in the far-field region,resulting in complex coherence effects,which will cause the far-field directional scattering characteristics and near-field enhancement effects of the nano-antenna to change significantly.But the intrinsic relationship between unidirectional scattering and multipole resonance is not very clear.In this thesis,the method of simulation is used.Based on the basic principle of localized surface plasmon resonance(LSPR).The Unidirectional far field and near-field enhancement characteristics of the metal nanorod antenna,the metal-high dielectric slice nanorod antenna,the metal trimer nanometer and the full dielectric trimer nanoantenna were numerically calculated by multipole decomposition of different optical resonance modes of the optical nanoantenna.The scattering efficiency and directivity of optical nano-antennas on light waves have been systematically studied.The regulation effect of optical nano-antennas on the scattering efficiency and directivity of light waves was systematically studied,and the relationship between the interaction between the multipole resonance of nano-antennas and the directivity of far-field scattering was elaborated,which provides theoretical guidance for the design of new optical nano-antennas.A gold-silicon slice nanorod antenna structure is proposed.Simulation results show that the optical nano-antenna can support multiple optical resonance modes such as electric dipole moment,magnetic dipole moment,and toroidal dipole moment.Moreover,the multipole resonance strongly depends on the size and material of the nano-antenna.The position of the resonance peak red-shift as the radius of the nano-antenna increases.The metal-dielectric material coupled antenna can reduce the material loss of a single metal material nano-antenna and excite the magnetic dipole moment and toroidal magnetic dipole moment resonance while maintaining the LSPR characteristics.The coupling between these resonance modes causes the enhancement of local electric field and magnetic field,and the far-field unidirectional scattering characteristics at multiple wavelengths are achieved.A high-dielectric silicon trimer nano-antenna is designed.Using theoretical calculations and numerical simulation methods,the silicon trimer nano-antenna is unidirectionally scattered at two wavelengths in the near infrared region by adjusting the nano-antenna resonance spectrum,which greatly enhances forward scattering and suppresses backscatter.Studies have found that it is possible to excite higher-order moments in the trimer structure by breaking the symmetry of the trimer.At the wavelengths of 816 nm and 1300 nm,the trimeric nano-antenna achieves approximately the generalized Kerker condition at two different wavelengths under multi-mode resonance coupling,further improving the scattering directivity.The effects of the nanoparticle material,geometry,and size parameters on unidirectional scattering in the far field and enhancement characteristics in the near field are also investigated.The formation mechanism of "magnetic hot spots" was explored,and its physical nature was explained using multimode coupling.Our results provide theoretical guidance for the future design and regulation of new near-infrared region all-dielectric material nano-antennas.