Study On Surface Lattice Resonance And Optical Chirality Enhancement Of Plasmon Structure

Chirality is the property of an object or molecule that cannot overlap with its mirror image and is an important concept in the fields of physics,chemistry and biology.Chiral materials will produce chiral-dependent optical response when they interact with circularly polarized light,in which circular dichroism is usually shown as the difference in the absorption of right-handed and left-handed circularly polarized light.As a special form of electromagnetic excitation different from the traditional electric and magnetic dipole,the toroidal dipole(TD)has many special response characteristics.However,toroidal dipole mode resonance response and the mutual coupling with electromagnetic field are weak,so it has not attracted much attention before.With the emergence and development of electromagnetic metamaterials,experimental observation of toroidal dipole has become possible.In recent years,nano-kirigami technology has gained widespread attention in the scientific community,forming a unique science of deformation from two-dimensional planes to three-dimensional structures.Here we reveal the first observation of the chiral SLRs that are formed by the coupling of chiral toroidal dipole moment and RA mode through theoretical design and experimental fabrication of a nanokirigami based propeller metasurface.The main contents of the paper are as follows:(1)In this work,we propose an effective yet simple scheme to manipulate the TDdependent chiral SLRs.After engineering the rotational symmetry of the propeller,e.g.from a triangle lattice with C3 symmetry to a square lattice structure with C4 symmetry,we find that the electric dipole chiral SLRs are evolved into the toroidal dipole associated chiral SLRs.Further,triangle and square lattice structures were prepared experimentally and the chiral toroidal dipole moment enhanced circular dichroism is verified in the near-infrared wavelength region.(2)In this work,we further propose a method to realize the resonant response of the toroidal dipole of the tunable square lattice structure.By changing the stereo twisted height of the square lattice structure,we find that the toroidal dipole excitation mode gradually overtakes the electric dipole as the dominant new mode as the height increases.(3)This work studies and summarizes the scheme to realize the inversion of triangle lattice and square lattice structure circular dichroism.The sign inversion of the triangle lattice structure circular dichroism can be achieved by changing the longitudinal coordinates of the structure source curve,and two methods that can achieve the CD inversion of the square lattice are summarized:the core idea is to change the stereo twisted height of the structure without changing the geometric chirality,which can be specifically by changing the deformation height of the structure or changing the curvature of the curve.(4)In this work,we propose two orthorhombic structures(window-like structure and simplified structure)and investigate in detail the optical chirality of the structures under the vertical incidence of circularly polarized light.The simulations reveal a special complete double-peaked waveform in the CD spectrum of the window-flower structure and an enhanced toroidal dipole resonance response of the simplified structure.This also provides a new idea for designing the structure for further research.