Study On Perfect Absorption Characteristics Of Metal/Dielectric Metasurface

Electromagnetic metamaterials,an artificially designed subwavelength size periodic structure,have unique advantages in the collection,transmission and control of electromagnetic wave energy which cannot be found in natural materials.Metamaterial absorbers can generate resonance response to enhance the absorption of incident wave by using special structural design,which have important research value in thermal photovoltaic devices,biosensing,radiative camouflage and nonlinear optics.Different from the traditional absorbers,which have strict requirements on the optical properties of materials,the metamaterial perfect absorbers can modulate electromagnetic parameters and regulate the light field to achieve perfect absorption.The subwavelength structure sizes make the devices more suitable for miniaturization and integration.Moreover,it can achieve the excellent performance of full angle absorption and polarization independent absorption simply for the specific periodic array structure.In this thesis,we systematically study the resonance absorption and spectral regulation characteristics of the metal/dielectric metamaterials,explore the physical mechanism of interaction between the incident light field and the absorber and the application of functional devices.The brief content of this thesis is as follow:The ultra-broadband perfect absorption from ultraviolet to near-infrared is achieved by using the two-dimensional periodic dielectric array of silicon carbide hemispheres and the tungsten substrate,through the magnetic dipole/grid and local mode resonance excitation.The average absorption rate of the whole band is up to 93.5%.The physical mechanism of broadband absorption induced by the magnetic dipole resonance and grid resonance excited in the dielectric hemisphere and high dissipation effect of tungsten caused by strong field capture is studied theoretically.The influence of square and hexagonal arrangement of hemispherical arrays in periodic plane on broadband absorption performance is investigated.The effects of incident angle,polarization direction and structure geometry on the absorption characteristics of silicon carbide hemispherical arrays are analyzed.The composite structure of silicon carbide hemispherical array and tungsten substrate can achieve efficient broadband absorption due to the excitation of independent multiple resonance response.Moreover,it has high tolerance to structural parameter error and is more suitable for large-scale fabrication due to the low precision requirement.Based on the metasurface composed of Al₂O₃ dielectric interlayer and periodic gold nano hemispheric particles on both sides,the coherent perfect absorption is achieved in the infrared range under the condition of multi-channel input.The relationship between the absorptivity and the phase difference of two coherent beams propagating backwards is studied in the mirror symmetric structure.The effect of hemispherical transverse distance on the coherent absorption characteristic of gold nanoparticles with non-mirror symmetry structure is discussed.Based on the independent response characteristic of different magnetic resonance,supercell structures with different hemispherical radii are designed to achieve dual-band coherent absorption in infrared regime.In order to obtain more freedom of tunability in the bilayer gold nanosphere array,a coherent perfect absorber with phase change material intermediate layer is used to achieves coherent perfect absorption with tunable frequency.The perfect absorption and dual-band spectral response are achieved in the infrared range by using the local surface plasmon resonance of gold split-ring-groove array excited by the transverse electric wave.The resonant absorption peaks with absorption rates of99.18%and 99.89%are obtained,respectively.The contribution of local surface plasmon resonance excited in split-ring-groove resonators with different central disk heights to dual-band absorption is analyzed.By applying gate voltage to manipulate the molecular orientation of nematic liquid crystal in the intermediate layer,the effective refractive index of the liquid crystal layer is changed.Thus,the red shift of the dual-band resonance peak is achieved by adjusting the dual-resonance response of the groove array.In order to achieve polarization independent dual-frequency absorption,a ring-groove array structure is proposed.The ambient refractive index changes will greatly affect the resonant wavelength of the dual-band absorption due to the field of the gold split-ring-groove array is localized in the surface grooves,thus the structure can be used as a high sensitivity refractive index sensor.In order to further improve the quality factor of multi-frequency absorption,a metasurface composed of a semi-cylindrical silica grating,a distributed Bragg reflector and a monolayer graphene is designed.The coupling mode theory is used to optimize the structure parameters,and the multi-frequency perfect absorption with high quality factor and tunability is achieved in the near-infrared regime.The characteristics of waveguide mode resonance of Si O₂ semi-cylindrical array and Bragg reflector and hybrid mode resonance between them are analyzed by means of the electromagnetic field distribution of finite difference time domain simulation.The relationship between the critical coupling condition of waveguide mode resonance and the period of semicylindrical array and incident angle of polarized light is investigated.By applying gate voltage to change the graphene chemical potential to control the waveguide mode resonance response,the dynamic modulation of absorption amplitude and quality factor is achieved.The switching function of all-optical switch is achieved based on the ultra-sensitive response of the ultra-narrow band absorber to the slight change of dielectric refractive index.