Study On Spontaneous Emission Of A Two-level Atom In Plasmonic Nanorod

Metal nanorod show excellent optical properties,the optical field can be confined within the region of subwavelength,even within nanometer.And since the plasmonic resonance frequency can be tuned by its aspect ratio.So they have huge potential application in many aspects.Recently,regulating the spontaneous emission of a two-level atom using surface plasmon effect has become a research frontier in nanophotonics.Based on local and nonlocal optical response models,the spontaneous emission enhancement of a two-level atom around the nanorod with a wide variety of dimensions or materials as well as dimer are systematically investigated by the finite element method in this paper.The main contents are as follows:In the first chapter,it briefly introduces that the basic concepts for surface plasmon and optical response models.Subsequently,the theory and numerical method for spontaneous emission are introduced.The full-wave simulation method and the Quasi-normal mode method for spontaneous emission are highlighted.In the second chapter,the resonance frequency and spontaneous emission enhancement of different nanorods have studied.Using Fabry-Pérot principle,the result shows that the resonance wavelength has a similar linear relationship with the aspect ratio of the nanorod if the decay length is neglected.However,the decay length is not neglected for shorter nanorod,but the resonance wavelength still has a better linear relationship with the aspect ratio.It is also shown that for a nanorod with the fixed length,the emission enhancement peak increases as the radius decreases.When the radius is fixed,the emission enhancement peak increases as the length is longer.In the third chapter,it systematically investigates that the effect of surface modification of metallic nanorod on the spontaneous emission of a two-level atom by the finite element method.Three different optical response models are adopted,including the local response approximation(LRA),the hydrodynamic model(HDM),and the generalized nonlocal optical response model(GNOR).The result shows the shapes,dimensions or materials have a great influence on the spontaneous emission.For a cylindrical nanorod with two endcaps,it is found that the resonance frequency shows large redshift and the emission enhancement peak increases as the endcap gradually changes from cone to cylinder of the same height.Spontaneous emission enhancement in silver nanostructure is better than gold with the same size.For bimetal core-shell nanostructure,the shell can screen the surface plasmons excitation of the core,and the plasmonic resonance associated with shell increases in proportion to the thickness of the shell.In the forth chapter,the spontaneous emission of a two-level atom for dimer with a wide variety of shapes,materials,dimensions or distances are calculated when the optical response for metal is under the HDM,the GNOR,and the LRA dispersion model.It is found the enhancement of spontaneous emission in the dimer is related to the gap or the distance between the QE and the metal surface.When the gap gradually decreases,an obvious redshift can be detected in the resonance frequency,the emission enhancement peak gradually increases at this time.Unlike the dimers with same size,the nonlocal optical response are significant in dimers of different sizes,and the spatial distribution of the coupled mode field varies widely.In the fifth chapter makes a brief summary and outlook about research work in the paper.