The Study On Optical Lattices And Phase Vortices In SPP Field Produced By Metal Nano-slits

Surface plasmon polaritons(SPPs)are electromagnetic surface waves arising from the couplings between electromagnetic field and collective oscillations of free electron charge density at metal/dielectric interface.Due to their special property,SPPs,a kind of evanescent wave,attracts widely interest in SPP focusing?SPP vortex and manipulation of the SPP field.In recent years,the research on the manipulation of SPP field is caught people's attention.There are many study on the generation of simple SPP patterns by using nano-slits and nano-holes.A lot of researches are developed on producing SPP vortex,as well.Since the limitation of the detection methods,the excitation efficiency and the existing theories of the SPP field,it is still difficult to generate some special patterns and high order phase vortices.The further research of manipulating the SPP field by nano-structures is needed.In this paper,we study the optical lattices and the phase vortices in SPP field by using the metal nano-slits.We theoretically employ the Huygens Fresnel principle and experimentally detect the results by scattering imaging method.In addition,the simulations of the SPP field are calculated by using the Finite difference time domain(FDTD solutions).We design different samples which have different number of slits arranging on different spirals.In theory,basing on the existing excitation parameters of SPP field,we use the Huygens Fresnel principle to derivate the expression of the SPP field excited by the samples.According to this expression,we obtain the numerically calculated results of the SPP field produced by FORTRAN.We experimentally study the SPP lattices by using a Mach-Zehnder interferometer system with microscopic objective to image the scattered SPP field.The interference intensity between the reference wave and the scattered SPP wave is recorded by the SCOMS.Then the information of different lattice patterns of SPP field are extracted by Fourier transform from the interference fringes.Moreover,we construct the auxiliary diffracting model of nano-stracture to analyze the mechanism of the lattice patterns.Basing on the interactions between incident light and metal,we design other samples with different topological charges to generate different higher order vortex lattice by using the FDTD solutions.This paper is consists of the following five parts.The first part is introduction,including the background of SPPs,the theoretical wave expressions of SPPs,the characteristic parameters of SPPs and the methods of excitation and detection of the SPPs.We introduce the application and research status of the SPPs,as well.Then we illustrate the purpose and the content of this paper.In the second part,we design the different structures of samples with different number of silts,and use the Huygens Fresnel principle and the existing characteristics of metal SPPs to derive the expression of SPP field which is excited by the samples with n slits.Basing on the theory,we obtain the simulation results of the SPP field under polarized light illumination.From the simulation results,it can be clearly seen that,in the situation of six-slits sample with m=1,six bright ring structures are formed along a ring to form the SPP Honeycomb lattice in the center of the sample.In the situation of six-slits sample with m=2,six bright spots form a kagome lattice.In the centre of the five-slits sample with m=1,there are five bright spots of light intensity distributed along the ring formed a five-petaloid lattice.In the case of seven-slits sample with m=1,seven bright spot make a seven-petaloid lattice.In the third part,we design the samples of metal structures with different number of silts,which are six-slits,five-slits and seven-slits samples.In experiment,we build a Mach-Zehnder type interferometer to observe the SPP field.We obtain the Honeycomb lattice pattern,the five-petaloid lattice,the famous Kagome lattice pattern and the seven-petaloid lattice,which are highly coincidence with the simulation results.Furthermore,we analyze the mechanism of generation of the lattice by constructing auxiliary model of six pinhole screen to explain the formation of the SPP lattices.In the fourth part,we design different samples consisted of different number of slits and different distributions along different helices.The vortices in SPP lattices with arbitrary higher order topological charges are generated under the left/right circularly polarized illumination.We use the finite difference time domain(FDTD)solutions to accomplish the numerical simulation and obtain both the SPP vortices with one order to five order topological charge and the corresponding SPP lattice of intensity patterns,such as Kagome lattice,Honeycomb lattice,five petals and seven petals shaped SPP lattice.In the fifth part,we summarize the achievements and innovations of the dissertation,and introduce the in-depth researches we will conduct.