The Generation And Regulation Of Magnetic Fano Resonance In Precious Metal Nanostructures

The metal is considered as plasma at normal temperature because the metal can be regarded as consisting of metal ions and free electrons.Under the excitation of the external field,free electrons perform collective oscillating motion and radiate electromagnetic waves with ions as positive background,Which quantification is called plasmon.Under the influence of the external field,the noble metal surface plasmon generates many unique optical properties(near-field enhancement,Fano effect,etc.)and is applied to many fields in scientific research,such as biomedical sensing,surface spectroscopy and Fano interferometer.The excitation of the surface plasmon resonance mode is related to the morphology and size of the nanoparticle.At the same time,the frequency shift of the plasmon resonance and the excitation of a new mode can be modulated by changing the geometric parameters of the nanoparticle and breaking the symmetry of the structure.Therefore,researchers have designed a variety of nanostructures and have been well utilized in engineering technology,such as nanoring structures,nanodisk structures,nanosphere structures,and the polymer structure and composite nanostructure composed of these basic units.Based on the achievements of the current research on surface plasmon photonics and its shortcomings in the research direction of magnetic Fano,we propose two noble metal nanostructures include the square spilt ring square ring nanostructures and the dimer nanostructure composed of square rings were analyzed by theoretical analysis and numerical simulation.This article is discussed by divided into three parts in the framework:The first part mainly introduces the numerical calculation method of scientific research,the second part introduces the optical properties of the composite nanostructures of square ring and spilt square ring,and the third part introduces the optical properties of square spilt ring dimers.First part:the three numerical methodsThe second chapter mainly introduces three kinds of numerical calculation methods,including finite element method,finite difference time domain method,and discrete dipole approximation.In this chapter,the principle of numerical calculation method is introduced one by one and the simulation software and features based on each method.This article mainly uses the COMSOL Multiphysics software based on the finite element method to simulation,therefore we has made the detailed introduction,but only gave the brief summary to the latter two methods.Second part:optical properties of square cleaved ring square ring nanostructuresIn this chapter,we designed a square spilt ring square ring composite structure and studied its optical properties.Based on the topological properties of the ring and the sphere is different,this composite nanostructure shows a wealth of optical properties.The calculation results show that there are kinds of resonance modes in the extinction spectrum of the nanostructures.From the corresponding charge distributions,it can be seen that the modes of the inner and outer rings are hybridized,and the position and spectrum width of the resonance modes can be adjusted by changing the geometric parameters of the structure.At the same time,the extinction spectrum also appears an asymmetrical Fano line type,and the Fano resonance can be regulated by adjusting the parameters and breaking the symmetry of the structure.In addition,the structure's local near-field enhancement and medium sensitivity to the surrounding environment are also quite high,therefore it has potential application value.Part three:Optical Properties of the square spilt ring dimer nanostructureIn this chapter,we have designed a polymer structure,which consist of a single nanoparticle.Compare with a single spilt ring,the dimer have more highly regulatory.From the homodimer to the heterodimer,due to the introduction of symmetry breaking,the structure appears a new mode and Fano resonance.Through the changes of homodimers,we have found that Fano resonance and it can be controlled,which can have a potential application prospect in the field of optical switches.What's more interesting is that we changed the arrangement of the structure,the structure also appeared an asymmetric Fano line type,and the near-field enhancement was also intense,which can be well applied to the field of surface-enhanced spectroscopy and optical elements based on magnetic Fano resonance.