Research On The Induced Chiral Optical Effect Of Metamaterials

Chirality refers to the characteristic that the geometric structure or spatial lattice can't coincide with its mirror image.It exists in most of the biological molecules in nature and is one of the basic attributes that nature and human survival.Therefore,the chiral detection of substances has become a research hotspot of scientific researchers.However,the chiral signal of natural chiral substances is very weak and locates in the near ultraviolet band,which greatly limits its detection sensitivity and application.Compared with natural chiral materials,chiral signals generated by chiral metamaterials can be several orders of magnitude stronger,and can be extended to visible and near-infrared bands,which has a very wide application prospect.However,the processing technology of most chiral metamaterials is complex,cumbersome and expensive.Therefore,it is very important to design a kind of chiral metamaterial with strong chiral effect.In this paper,a heterogeneous reticulated chiral metamaterial(HRCM)structure is proposed,including planar and three-dimensional structures.The mechanism of circular dichroism and circular dichroism are studied,respectively.The main research work is as follows:(1)A planar heterogeneous network chiral metamaterial(PHRCM)structure composed of a gold grid and a silver grid is designed.The composite structure composed of the gold grid and the silver grid that are not orthogonal to each other destroys the symmetry of the spatial distribution of dielectric constant and made the structure chiral.The structure can generate a larger CD signal in the visible light band.The finite element method(FEM)was used to study the surface plasmon resonance coupling characteristics between the gold grid and the silver nanorods that constitute the structural unit.Under the excitation of light with different rotation directions,the resonant coupling modes are different,causing the difference in absorption and finally producing circular dichroism.By optimizing the structural parameters of the composite structure,the heterogeneous network chiral metamaterial structure can obtain obtain up to 40% CD signal,which is better than most chiral planar metamaterial structures.(2)Furthermore,a three-dimensional heteroreticular chiral metamaterial(3d-hrcm)structure was designed.By changing the thickness of gold gate or silver gate in the composite structure,the difference in them was introduced to further destroy the symmetry of the structure.Compared with the planar chiral structure,the threedimensional heteroreticular chiral metamaterial structure can effectively enhance the absorption coefficient of the structure excited by RCP and further enhance the CD signal.By optimizing the structure parameters,the maximum CD signal is 45%,which is 12.5%higher than that of planar structure.(3)A laser double grating interference system was built,and the preparation process of chiral structure was studied.By optimizing various parameters of gluing,prebaking,exposure,and heterogeneous chiral metamaterials with good quality were prepared.The experiment results shows than the CD signal is 22%,which proved that the structure had good chiral effect.