The Oretical Study Of Four-wave Mixing In Metallic Nanostructures

The surface plasmons at the regime of evanescent can be obtained by four-wave mixing (4WM) propagating angularly on the surface of the metal. By adjusting the angles of incidence lights, the propagating direction of surface plasmons can be controlled. However, due to the weak penetration of metal, the excitation efficiency of surface plasmons is very low as well as the conversion efficiency of4WM. Therefore, based on this issue, this paper aims at improving the conversion efficiency of4WM, enhancing the intensity of four wave mixing and analyzing the factors which influence the intensity of4WM. The whole paper is divided into several parts as follows:First, the analytical solution of the four-wave-mixing signal at the planer of metal is studied. We obtain the differential equation of four-mixing signal at the planer of metal by combining the function equation of light and matter based on Maxwell equations. Through analyzing the differential equations, the general form of analytical solution of electric field four-mixing signal at the planer of metal is obtained. By further adopting the corresponding boundary conditions, the definite solution of four-wave-mixing is obtained.Second, the factors which have influence on the signal intensity distribution of four-wave mixing are analyzed. By conducting the numerical simulation to the analytical solution of electric field, we obtain the relation of four-wave mixing signal intensity distribution and the incident angle of the incident light. Furthermore, we obtained the best excitation angle to excite the surface plamons and enhanced the efficiency of surface plamons excitation.On this paper, two nanostructure of metal are designed to enhance the signal intensity of4WM and improve the conversion efficiency of four-wave mixing in metal. For the two destinations, one structure is designed by depositing a thin dielectric layer on the metal surface. The other is designed by reducing the thickness of the metal film. By analyzing the intensity enhancement of metal plane4WM at dielectric-metal structure, depositing a thin dielectric film at metal enables us to enhance four-wave-mixing at metal planer by up to two orders of magnitude at633nm signal at TM polarization. Based on the analysis, the four-wave mixing signal strength of the20nm-metal film is6times of that of a thicker metal film. We also optimized the excitation angles at a52nm thickness metal film, At the optimized angle, the intensity of surface plasmons on52 nm metal film is2times larger than that of the metal planers.