Theoretical Study Of Multiphoton Induced Surface Plasmon Polarizations Based On Four Wave Mixing

In ultrafast nanophotonics,a possible solution to improve the nonlinear efficiency is to obtain local strong field on the solid surface.Surface plasmon polarizations are a kind of electromagnetic oscillation at the interface between metal and dielectric,which can localize the field in the subwavelength scale and has significant local field enhancement effect.However,they are difficult to be excited directly by a single beam of incident light.In general,additional structures such as prisms,gratings or nanospheres are needed to satisfy the momentum matching.These excitation methods require advanced technology,and generally use specific manufacturing solutions for specific problems,lack flexibility and greatly add the cost.In this thesis,nonlinear optics and surface plasmon polarizations are connected.Based on the multiphoton process in four wave mixing(FWM),the excitation of surface plasmon polarizations on a single interface of metal and dielectric is studied.Because the nonlinear signal propagates locally on the interface in the form of surface plasmon polarizations,the four wave mixing effect on metal surface is enhanced.In this thesis,the characteristics of surface plasmon polarizations excited by four wave mixing at the interface between gold and quartz are studied by theoretical model and software numerical simulation.The main research contents include:(1)Based on the multiphoton process,the condition parameters to excite the surface plasmon polarizations are calculated.The theoretical model of the four wave mixing effect on the metal surface is established.(2)A scheme based on finite-difference time-domain algorithm for a double-layer structure of metal and dielectric is proposed.In addition,the two-dimensional simulation of surface plasmon polarizations excited by four wave mixing on the single interface betweeen gold and quartz is established by using the software.The results show that when surface plasmon polarizations are excited,the electric field intensity of the four wave mixing signal with 633 nm wavelength can be increased by two orders of magnitude,and this process has selective polarization angle and incidence angle of the incident beam.The time domain signals of the surface plasmon polarizations are obtained,and the energy relationship between the incident laser and the surface plasmon polarizations is studied.The process accords with multiphoton energy relation in weak field,but it is not suitable for strong field.(3)Based on the damage mechanism that plasma is produced by femtosecond laser ionization of quartz,the threshold of incident light intensity in the process of surface plasmon polarizations excited by four wave mixing is calculated by using a program.Moreover,the highest conversion efficiency of four wave mixing is predicted.