Unidirectional Excitation Of Surface Plasmon Polariton Induced By The Hermite-Gaussian Beam

The SPP source with good unidirectionality and high excitation efficiency has important application requirements in nanophotonic integration and nanometer measurement.In this dissertation,we study the interaction between higher-order mode Hermite Gaussian beams and nano-slits,slit pairs and nanoholes on the metal thin film,and develop new methods for asymmetric SPP excitation.Because the high-order Hermite Gaussian field has a π phase transition and a large gradient of light intensity on both sides of the dark line,the asymmetrical SPP will be excited when it is misaligned with the symmetric nanostructure.Through theoretical analysis,we have given the SPP excitation model of nano-slits,slit pairs,and nano-hole array structures on metal thin films.Finite-difference time-domain(FDTD)simulations and theoretical analysis have shown that the metal slit array structure can obtain more significant asymmetric SPP excitation in the case of sub-wavelength misalignment coupling.Further,we processed various nanostructures using a focused ion beam(FIB)etching method,and verified the above theoretical analysis and numerical calculation results using leaked radiation microscopic imaging methods.The experimental results verify the effect of the asymmetric excitation of SPP on the interaction between the high-order Hermite Gaussian field and the metal slit.The use of high-order Gaussian beams and metal slit array structures enables the dynamic regulation of the SPP excitation direction,providing a new method for detecting subwavelength shifts,which has important application value in the field of nanometer measurement technology and other fields.This article mainly includes the following aspects:(1)We studied the properties of the first-order mode Hermite Gaussian optical intensity and phase distribution discontinuity.The first-order mode Hermite Gaussian beam was numerically simulated using the finite-difference time-domain method in the study,and the Gaussian light of the HG10 mode was generated experimentally using a radial polarization converter and a polarizer.(2)Comparing with the existing asymmetric SPP excitation method,we propose a theoretical model based on the metal slit structure to achieve dynamic regulation of the asymmetric excitation of SPP.The metal double-slit array model is further proposed to achieve more significant asymmetric SPP excitation.Combined with the principle of SPP interference and dipole interaction,the metal slot model and the metal slot array model were theoretically analyzed.FDTD was used to simulate the near field distribution and far field distribution of the metal slit model and the metal slit array model,and the physical process of the asymmetric excitation SPP and the dynamic regulation of the scattering field direction and the splitting ratio were verified.(3)A metal slit array structure was fabricated on a 50 nm thick silver film using a focused ion beam(FIB)etch.The asymmetric excitation effect was experimentally verified using leakage radiation imaging system.The experimental results verify the effect of the asymmetrical excitation of SPP by the interaction between the high-order Hermite Gaussian field and the metal slit.At the same time,the dynamic tunable characteristics of this asymmetric excitation effect are also proved.The innovations of this paper mainly include:(1)For the first time,we propose the use of a high-order Hermite Gaussian beam as the incident light,focusing incident on the metal slit structure and the metal slit array structure,and realizing the asymmetrical excitation by adjusting the relative position of the higher-order Hermite Gaussian light singular dark line and the structure.(2)We combine the dynamic control of the SPP transmission direction and the scattering split ratio with the tiny displacement at the nanoscale location.By controlling the change of the relative position of the strange dark line of the HG10 beam and the structure of the metal slit array,the split ratio of the asymmetrical SPP excitation is gradually increased.This has important application requirements in nanometer measurement technology and nano-scale displacement sensors.