Study On Terahertz Wave Absorption Properties Based On Bulk Dirac Semimetal Metamaterial

Metamaterials are artificially designed subwavelength structures with exotic properties that are different from those of natural material structures and have the advantages of strong absorption,small size,and customizable electromagnetic properties.In recent years,metamaterials can effectively enhance the sensitivity of terahertz（THz）functional devices and played an important role in the development of sensing,radar,and stealth technologies in the THz band.However,the inherent loss of metamaterials（i.e.,absorption loss）is a frequently encountered disadvantage that usually degrades their resonance performance.Therefore,how to achieve low loss is an important direction of metamaterials research,including the use of low-loss materials or gain materials,and optimization of structural design to reduce or even suppress the absorption loss of metamaterials.In recent years,the concept of metamaterial perfect absorber（MPA）has been proposed to make the inherent loss of metamaterials favorable.Due to the ability of MPA to achieve perfect absorption of THz waves,MPA shows great promise in many fields such as material detection,biosensing,and microbolometer.The works in this thesis are based on tunable metamaterial structures,photonic device models constructed using FDTD（Finite Difference in Time Domain）software,and the resonance mechanism of the metamaterial devices to THz waves and the modulation method are investigated in depth.The work in this thesis and the research results are as follows:In the THz region,an MPA is proposed and numerically analyze,which consists of a periodic array of Si O₂ disks and a bulk Dirac semimetal（BDS）reflection layer.Due to the low loss property of Si O₂ in THz band,the device achieves the perfect ultra-narrow band absorption of THz wave.Based on the high plasticity of MPA,perfect absorption can be achieved under different combinations of parameters,which provides guidance for achieving resonance at specified wavelengths.Meanwhile,the active modulation of resonant absorption can be achieved by changing the Fermi energy of the BDS.Furthermore,it was confirmed that the MPA is sensitive to the surrounding refractive index up to 70.2μm/RIU.It is expected that this ultra-narrow-band MPA has potential applications in biosensing and THz narrow-band filtering,etc.An MPA based on a BDS resonator and an opaque gold reflector layer is proposed.Since BDS exhibits a metallic response in the THz band and its dielectric constant is actively tunable,this makes the BDS-based device have the advantage of ultra-high quality factor（Q-factor）and dynamic tuning.The proposed structure achieves near-perfect ultra-narrow-band absorption of THz wave.The absorption performance of the device can be flexibly tuned by employing different periods,widths,and thicknesses.Also,by reducing the thickness of the BDS layer,the Q-factor of the device is significantly improved,up to 4133 at smaller thicknesses.In addition,the device proved to be highly sensitive to the surrounding refractive index,with a sensing sensitivity figure of merit（FOM）as high as 4125.It is expected that the proposed design and developed method can have practical applications in future THz filtering,detection and sensing.A BDS-based dual-band MPA is proposed,whose structure consists of a material BDS square array embedded in a dielectric layer on the BDS reflection.In using the new material BDS,two different modes are integrated into a simple structure instead of shaping a complex metamaterial structure.Numerical analysis shows that the two resonance peaks of the MPA are attributed to the local cavity resonance and the intercellular electrical resonance,respectively.The absorption frequency of this absorber can also be dynamically tuned by varying the Fermi energy of the BDS.Meanwhile,the relaxation time of the BDS can be used to control the absorption intensity with constant absorption peak position.In addition,the proposed absorber is polarization-insensitive to the incident light due to the symmetry of the metamaterial structure.Therefore,this work can provide guidance for the research of THz dual band simple structure MPA based on BDS.