Study On The Chiral Optical Characteristics Of Strong Coupling Systems Of Surface Plasmons And Excitons

The strong coupling between a local cavity mode field and a quantum system is one of the important topics in quantum information science and technology.Its realization is not only of great significance for our development of basic quantum theory,but also provides a foundation for our exploration of high-end quantum applications.Compared with the traditional solid-state optical microcavity,the surface plasmon micro-nano structure has the advantages of ultra-small mode volume and strong coupling at room temperature,so it has attracted great interest.In the strong coupling state,the energy exchange between the light field mode and the exciton system occurs strongly and rapidly,and a new optical hybridization state,plexciton hybrid states,is generated.This hybrid state has the characteristics of both surface plasmon and exciton,and shows the mode splitting in spectroscopy and the anticrossover in dispersion curve.Understanding and revealing the basic optical properties of plexciton hybrid states is of great value for many quantum optical applications,such as thresholess lasers,quantum information processing,and quantum multi-body networks.At present,the hybrid states formed by strong coupling between surface plasmons and excitons are just studied,and the understanding and study of their basic properties are not perfect.Especially when coupled system containing a chiral structure,chiral optical properties of plexciton hybrid states are still seldom reported,and studying the strong coupling of surface plasmon and exciton in the view of chiral optics not only provides a new perspective for us to understand the interaction of strong light objects in the surface plasmon microcavity,but also provides potential possibilities for the realization of chiral optics applications such as chiral sensors,non-reciprocal quantum devices,chiral control,etc..Based on this,this thesis has systematically studied the chiral optical properties of a variety of different surface plasmon micro-nano structures and exciton strong coupling systems in theory and experiment.The related research contents include the following aspects:1.The gold-silver nanocomposite particles with ultra-small mode volume were synthesized,and a strong coupling system of chiral J aggregates and metal nanoparticles was constructed by adsorbing chiral J aggregates on the surface of the particles.By measuring the extinction and the circular dichroism(CD)spectroscopy of the system,the chiral and achiral optical response of the chiral J-aggregates and metal nanoparticles strongly coupled system are obtained.By adjusting the resonance of metal nanoparticles,we studied the evolution of the spectral characteristics of the coupling system with the detuning of surface plasmons and excitons.The experimental results show that in the strong coupling state,the plasmon-exciton hybrid state exhibits typical strong coupling characteristics such as mode splitting and anti-crossing behavior not only in the extinction spectrum,but also in the CD spectrum.This indicates that the energy exchange of the system under strong coupling will not only lead to the hybridization of the achiral optical properties of the system,but also the hybridization of the chiral optical properties.The coupling system observed 136 meV and 211 meV mode splitting on the CD spectrum and the extinction spectrum respectively.Although the mode splitting observed from the CD spectrum was smaller than the extinction observation,the line width of the CD signal was still narrow.Two new hybrid modes produced by strong coupling can be identified.2.A new theoretical model is proposed to solve the interaction between metal nanoparticles and chiral exciton media.This model mainly studies the interaction between metal nanoparticles and chiral excitons by solving the polarization characteristics of metal nanoparticles placed in a chiral exciton medium under quasi-static conditions.Our theoretical results reveal the interaction between metal nanoparticles and chiral excitons.We have theoretically confirmed that strong coupling will lead to mode splitting and anti-crossing behavior on the CD spectrum,and at the same time reveal the distinction and connection between the extinction response and the CD response of the coupled system.Furthermore,we also provide a new set of strong coupling criteria based on the split difference between CD and extinction modes.3.In the experiment,DNA origami technology was used to design and synthesize a three-dimensional chiral nanorod dimer composite structure.By adsorbing dye molecules,strong coupling between the chiral metal nanocomposite structure and excitons was realized.Experimental results show that strong coupling can greatly change the optical response of the metal nanocomposite structure,and induce transparency near the original extinction and CD spectral resonance peaks.We use the coupled oscillator model and the finite difference time domain(FDTD)simulation method to study and reproduce the experiment phenomenon.The results show that the induced transparency is the result of energy level splitting caused by the coupling of the antisymmetric mode supported by the dimer complex structure and excitons.Comparing the extinction and CD spectra,we found that due to the bisignate CD line shape of the chiral dimer,we can directly distinguish the two hybrid branches generated by the antisymmetric mode and the exciton coupling from the CD spectrum of the coupling system.It is difficult to distinguish each resonance mode directly on the elimination spectrum due to the wider spectral linewidth.By adjusting the resonance energy of the surface plasmon,we also obtained the energy evolution picture of the hybrid branch generated by the strong coupling between the antisymmetric mode and the exciton from the CD spectrum,and showed the anti-crossing behavior of the two hybrid branches.