Research On Terahertz Sensing Method Based On Toroidal Dipole Resonance In All-dielectric Metasurface

Terahertz wave has the characteristics such as low energy,non-ionization and high penetration,and most molecules exhibit strong absorption in the terahertz regime.Thus,the terahertz-based biochemical sensing method has become a research hotspot.All-dielectric metasurface,artificial completely nonmetallic materials consisting of periodically arranged sub-wavelength elements,exhibits unique electromagnetic properties.Toroidal dipole(TD)with weak coupling to the electromagnetic fields can confine the electromagnetic energy in metasurface and enhance the light-matter interactions.Therefore,two kinds of terahertz sensor based on TD resonance in all-dielectric metasurface are proposed in this paper,which can realize the qualitative identification and quantitative analysis of trace analyte.The main research work in this paper is described as follows:(1)A terahertz all-dielectric metasurface based on electric TD is designed.Two distinct TD resonances governed by bound states in the continuum(BIC)are excited.One is distinguished as intracluster TD mode,and the other one is intercluster TD mode.The TD resonances can transform from BIC to quasi-BIC with high quality factor(Q factor).The TD resonance with high-Q factor is very sensitive to the change in the refractive index of trace analye,achieving ultrahigh sensitivity level of 489 GHz/RIU and a corresponding figure of merit of 25352,and realizing ultrasensitive sensing at terahertz regime.(2)A terahertz all-dielectric metasurface based on magnetic TD resonance is designed.The TD resonance is excited at the 529 GHz.The corresponding big electric field enhancement at the air slot(about 205)is beneficial to enhance the absorption of terahertz wave by the target analyte,making the characteristic information of the target analyte more obvious.The results show that the target analyte and non-target analyte can be distinguished effectively according to the TD resonance intensity variation.And qualitative analysis of the target analyte can be realized based on the attenuation of the TD resonance intensity.(3)The machining and test scheme of the all-dielectric metasurface sensor are designed.The machining technology of the sensor is mainly based on photolithography technology,coating technology,stripping technology and reactive ion etching technology.The sensing test equipment and sensing test method are introduced in the test scheme of the sensor.The machining and test scheme of the all-dielectric metasurface provides a way for theoretical research to application in the terahertz-based biochemical sensing.