Study Of All-optical Dynamic Manipulation Of Surface Plasmon Polaritions Based On Focused Optical Vortices

Surface plasmon polaritions (SPPs) have received considerable attentions in diverse applications, such as optical signal process, surface enhanced spectroscopy and sensor technology, with specific contributions to control, enhancement and confinement of the surface field. Traditionally, the local SPPs can be created and controlled by nano-particles or patterning metal surface. But the conventional methods have some limitations to reduce the SPPs excitation efficiency and controllability, such as operational complexity, light scattering, absorption loss and unreconfigrability. Complementary to the patterned metal surface technique, the all-optical method for generating, localizing and controlling SPPs has important potential applications.In this paper, we propose to localize and control the SPPs all-optically on the flat metal surface. Owing to the axially symmetric, depolarization and significant electric field enhancement effect of radially polarized beam and spiral phase characteristic of optical vortices (OV), the SPPs could be shaped optimally into the complex field patterns of certain amplitude and phase profile. The generating, propagating and interfering of SPPs are controlled and modulated by focused radially polarized OV beam. And the SPPs vortices with spiral phase are generated on the metal surfaceFrom the above, based on the beam shaping and the focused beam technique, the major content and result are shown as follows:Firstly, the dynamic SPPs landscapes are generated in the predefined position by using a highly focused vortex beam imaged onto a uniform flat gold (Au) metal surface where the surface plasmon resonant (SPR) angle is satisfied. Using the total internal reflection fluorescence microscopy (TIRFM) technique, Fluorescence excited by the SPPs field near the metal-dielectric interface is used to image the surface plasmon patterns experimentally. The propagation and distribution of SPPs field depended on the incident conditions, such as the size, shape and polarization of incident beam and incident angle, are analyzed quantitatively.Secondly, without metal structures, the locally induced SPPs can further be propagated following the predefined patterns to form symmetric focal spots with dimensions beyond diffraction limit. The focused SPPs field is modulated into the special axially symmetric array. FWHM of the SPPs spot on the primary intensity ring is calculated as being 0.3λ0.The proposed model of SPPs focusing by the vortex mode was described in detail based on the focused beam technique. We theoretically discuss the physics involved in the beyond-diffraction-limit focusing phenomenon and the unique characteristics of dynamic focused SPPs patterns using the vectorial diffraction theory. By performing the 3D-FDTD simulations, the proposed focusing model was verified by comparing the difference of field distributions with and without the metal film.Lastly, SPPs vortices excited by a highly focused radially polarized optical vortices beam on a metal surface are proposed with analytical and numerical verifications. Complementary to the spiral grooves and plasmonic vortex lens for generation SPPs vortices reported in literature, the proposed method reveals a direct transform from optical vortices to surface plasmonic ones with dynamic, reconfigurable and high efficiency advantages. The plasmonic field pattern, phase distributions, Poynting vector and focusing efficiency of SPP vortices are demonstrated in detail.Through the investigation of all-optical modulation and control of SPPs by optical structure light-vortex beam, the conclusions draw in this thesis is helpful to the design of near-field interference sensor, super-resolution microscopy and optical data storage applications.