| Terahertz owns many unique properties not found in other frequency bands,which has been one of the fastest growing fields over the past decades.Metamaterials,especially for metasurface,provides a new route for terahertz functional devices.Now,most metasufaces are based on the periodic structures,aperiodic distributions show another route for achieving it.In this dissertation,we investigated terahertz metasurface lenses,polarization device,surface plasmon device and absorber based on both periodic and aperiodic patterns.1.We proposed a highly efficient metal-dielectric-metal structure that operates range from 0.75 to 1THz.By varying the geometrical parameters,three broadband and robust metalenses with linear,quadratic and cubic phase profiles are proposed efficiently manipulates the spatial distribution of the terahertz field.The proposed flat metasurface lens design can focus wave to a spot size of subwavelength from 0.75 to 0.95 THz and achieve a transmittance efficiency of 45%.All of which are experimentally investigated by using near-field scanning terahertz microscopy(NSTM).In addition,the NSTM system facilitates an experimental investigation of the incidence angle dependence of the terahertz metalens,which proves the robust focusing feature of the proposed device.2.Based on two periodic distributed dielectric pillars,we proposed an efficient approach for broadband,high-quality polarization rotation operating in transmission mode with all-dielectric metamaterials in the terahertz regime.Different from the conventional way of controlling the phase of orthogonal polarization components,we obtain rotated output waves with a conversion efficiency of 67.5% from 0.5 to 1.4 THz by rotating the orientation angle of dielectric pillars.The proposed polarization manipulation strategy shows impressive robustness and flexibility in designing metadevices of both linear and circular polarization incidences.3.Previous works on 2D quasicrystal distributed have mainly focused on transmission,photonic band gaps and optical modes in the far field.However,the behaviors of SPs in QCMs remain unexplored.(1)Transmission and plasmonic resonances of quasicrystal metasurfaces were studied.The transmission minima resulting from Wood's anomaly are directly related to the surface plasmon resonances.We also find that the surface plasmon resonances of the quasicrystal metasurface were determined by the reciprocal vectors,which could be well explained by the coupling condition of the resonances,and the characteristic frequencies remain un-shifted under various slit sizes.(2)Propagation of the Surface plasmons on quasicrystal metasurface exhibits distinct characteristics that are fundamentally different from that of periodically and randomly arranged metasurfaces are demonstrated using analytical theory and near-field measurements.This unique approach paves the way towards promising applications in the excitation and control of near-field SPs.(3)The N-fold quasicrystal metasurfaces reveal multidirectional surface plasmon propagation determined by their reciprocal vectors.With properly designed paired slits,surface plasmon distributions of quasicrystal metasurfaces can be controlled by light spin-state.The surface plasmon patterns of the quasicrystal metasurfaces are found to be the product of quasicrystal arrays and single slit pattern by introducing the array factor.It characterizes the ability of the quasicrystal arrays to transfer free space energy to a desired directional emission of surface plasmons.4.By investigating the response of metamaterial absorbers based on periodic,Fibonacci,Thue-Morse,and quasicrystal lattices,we found that aperiodic-metamaterial-based absorbers could display similar absorption behaviors as the periodic one in one hand.However,their absorption behaviors show different tendency depending on the thicknesses of the spacer,which are demonstrated by equivalent impedance analysis.Further studies on the angle and polarization dependence of the absorption behavior are also presented. |
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