Actively Tunable Extrinsic Chirality Of Metasurface For Terahertz Wave

Due to its special electromagnetic characteristics,terahertz waves have been applied in many fields such as imaging and detection.Terahertz technology has also become a hot spot in domestic and foreign research and has an immeasurable development prospect.As an artificial two-dimensional electromagnetic material capable of controlling electromagnetic waves,metasurfaces have gradually entered the field of vision of researchers in recent years,and terahertz functional devices made of metasurfaces have emerged as the times require.This thesis mainly focuses on the chirality characteristics of terahertz waves,and studies the method of using metasurfaces to generate extrinsic chirality in the terahertz band and the active control method of extrinsic chirality,which can be divided into two parts:On the one hand,according to previous research results,extrinsic chirality is a special kind of chiral electromagnetic response.It only needs to change the angle between the incident light and the metasurface to achieve active control of chirality.This thesis designs a metasurface structure with extrinsic chirality,explores the relationship between the oblique incidence angle of terahertz waves and circular dichroism,and confirms the generation of extrinsic chirality.In addition,when applying a continuous laser on the metasurface,the active control of the extrinsic chirality is also realized by changing the power of the laser.Also,the influence of silicon carrier layer thicknesses on the chiral modulation depth is studied.In the experiment,the generation and active control of extrinsic chirality were also successfully realized.On the other hand,as a typical phase change material,vanadium dioxide is often used in the field of metamaterials to achieve active control of electromagnetic waves.In this thesis,another kind of terahertz metasurface with extrinsic chirality is designed.On the basis of generating extrinsic chirality through oblique incidence of terahertz waves,and by changing the phase transition state of vanadium dioxide on the metasurface,the active control of extrinsic chirality is also realized.Since the concept of extrinsic chirality was proposed,researchers have carried out some structural design and functional innovations,but as far as I know,there is no example of active control of extrinsic chirality,so the thesis has certain research value and application prospects in the field of chiral active control of metasurfaces.