Study On The Properties Of The SPPs Standing Wave Field Excited By A Tightly Focused And Radially Polarized Vortex Beam

Under certain condition the photons of incident light interact with the freeelectrons on the interface of metal/dielectric to generate collective resonate eachother and excite surface electromagnetic wave propagating along the dielectric/metalinterface which is the surface plasmon polaritons (SPPs). The local SPPs are a state ofexcited evanescent wave which is propagated on the surface of dielectric. The SPPswith a higher spatial frequency can break through subwavelength interference limitfor its near-field enhanced characteristic. Based on these properties, the SPPs haveplayed a key role in the development of modern science and technology with a wideapplication in many areas.At the beginning, most of works on the SPPs reported are focused on the caseswhich are excited by the use of Gaussian beam. However, when utilizing Gaussianbeam to generate SPPs, the transmitted field component of Gaussian beam can disturbthe main peak of the SPPs interference field and thus lead to the decline of visibilityof the interference pattern. But the vortex beam has a dark spot in the spin central andits field intensity is equal to zero. To compare with the other excitation modes, thetightly focusing has a larger incidence angle spectrum. It is conducive to the excitationof SPPs. In addition, the radial polarization has special advantages in the excited SPPsand the field intensity distribution is centrally symmetric. In this paper, we use themethod of angular spectrum representation to study the characteristics of a SPPs fieldinduced by the vertical incident radial polarization and tightly focused on a vortexbeam and compare it with that resulting from linear polarized vortex beam andradially polarized Gaussian beam. Meanwhile, in order to improve the performance ofSPPs photonic devices, it is still very important to further study the properties of theSPPs self-interference. According to the parameter’s variability of SPPs, we focus onthe analysis of the influences of some important factors on the SPPs standing wavefield and also make comparisons between an Au/air interface and an Ag/air interface.Subsequently, the case of different incident wavelengths is considered and the resultsindicate that there is an optimized value of metal film thickness in the process and thefield intesity of SPPs is sensitive to the change of refractive index of substrate materials. The SPPs standing wave field strongly depends on the maximumdivergence angle and the refractive index of dielectric substrate. With the increasingloss coefficients of metal, the maximum field intensity of the SPPs centralinterference ring will decrease for the reason of ohmic losses. Additionally, the changeof the topological charge could affect the shape of SPPs interference fringe. As atypical example, we make a comparison of the SPPs standing wave field distributionwhich is formed on Au and Ag film respectively. At last, the SPPs standing fieldinduced by different incident lights is considered. Based on the analysis above, thestudy of the thickness of metal film, the refractive index of dielectric substrate, andthe number of topological charge can provide theory supports for sensor production,the imaging and manipulation of biological molecular, and the optical storage ofsubwavelength, etc.