The Study On The Designing And Optimizing Metallic Nanoantennas To Enhance The Interaction Between Light And Matter

Profiting from the rapid development of nanotechnology and Characterization technique,Surface Plasmons(SP)in metallic nanostructures have currently become one of the most active research topics in the field of physics,chemistry,materials science,information science,biology,and their interdisciplines in the past decades.SP can propagate in structures beyond light diffraction limit and extremely enhanced the local electromagnetic field,which are useful for nano optical devices,enhanced Raman spectra and ultra-sensitivel detection.And some research achievements have already been applied in our life.Meanwhile,it has merged into a new rapidly growing discipline,called surface plasmonics,which covers the research area of physics,chemistry,material science,information science,biology,and their inter-disciplines.In this thesis,we will give detailed studies on the designing and optimizing metallic nanostructures to achieve better performance of optical antenna and tailor fluorophores' emission properties.Meanwhile,we will propose a dimer nanostructure with double interface to enchance optical field beyond the limitation of quantum effects in tunnelling plasmonics.In addition,we will theoretical study on the physical properties and operation quality of multi-wavelength spaser.The thesis is mainly composed of four sections that are arranged as following:1.We will give a detailed introduction about the physical conception,characteristics,and basic features about surface plasmon polaritons.Additionally,we will also overview the research development,current status and application potential of three important surface plasmonic research areas for:optical antenna,quantum plasmon and nanolasers based on plasmonic resonators.2.Tailoring fluorophores' emission properties with optical antenna.We present a novel amplification scheme by introducing double(another)interface around the traditional plasmonic nanoantenna to fully utilize the 'hot spots'.Here the fluorescence amplification is provided due to dielectric interface around metallic nanoparticles which produces a large discontinuity of the electric field at the interfaces with 'hotspots' transferred to the dielectric-air interface.A dielectric layer also helps to minimize the nonradiative losses incurred by the metallic constituents reducing the quenching effect.For traditional optical antennas,there was only one interface of metal and environment and the optical field enhanced 'hot spots' are localized at the interface.In order to maximize excitation field,the fluorophores should be placed in localized 'hot spots' close to the interface.However,in this situation,nonradiative energy transfer from fluorophores to metal caused by dissipation in the metal is enhanced,so the decrease of quantum yield wins over the increase of the excitation field thereby quenching the fluorescence of the fluorophores.We give experimental validations of our theoretical results on that the maximum fluorescence enhancement can be achieved by introducing a dielectric interface with an optimal dielectric constant and an appropriate thickness.Moreover,this approach can be extended to optimize other plasmonic nanoantennas such as cascaded self-similar nanoparticles for FE.3.We propose a dimer nanostructure with double interface to enchance optical field beyond the limitation of quantum effects in tunnelling plasmonics.Plasmonic nanostructures enable light to be concentrated into nanoscale 'hotspots',wherein the intensity of light can be enhanced by orders of magnitude.This plasmonic enhancement significantly boosts the efficiency of nanoscale light-matter interactions.Large enhancements are often observed within narrow gaps or at sharp tips,as predicted by the classical electromagnetic theory.Only recently has it become appreciated that quantum mechanical effects could emerge as the feature size approaches atomic length-scale and quench optical field.We propose a dimer nanostructure with double interface to effectively prevent the quantum tunneling,making optical field beyond the limitation of quantum effects in tunnelling plasmonics.In this situation,the Raman intensity can be 25 times stronger compared with traditional dimer nanostructure.4?We propose a novel multi-wavelength spaser based on whispering-gallery resonances in hyperbolic spherical cavities.Purcell factor,mode volume and quality factor are important parameters for spaser.Many approaches have been raised to achieve spasers with subwavelength physical size,low lasing threshold and high directionality by using plasmonic structures assisted by an optical-gain medium.Spasers based on propagating surface plasmons exhibit high quality factors but hard to be integrated for their large cavity size compared with wavelength.Unlike propagating surface plasmons based spaser,localized surface plasmons based spaser can achieve ultra-small mode volume but electro-static nature of such resonators limits the quality factor of the cavities because of radiation and metallic losses associated with high lasing threshold.Fortunately,the progress in hyperbolic metamaterials provides new opportunities to design a subwavelength spaser with low lasing threshold.Hyperbolic metamaterials have a negative dielectric constant in at least one direction,exhibit unusual hyperbolic dispersion and are capable of confining fields with deep subwavelength cavity sizes.Recent theoretical research indicates that hyperbolic spherical cavities supporting whispering-gallery modes can take advantages of both propagating surface plasmons and localized surface plasmons with high Q factors and deep subwavelength volume.We expect that the proposed design is a promising path to be integrated to photonic circuits.