表面等离激元与激子多元耦合特性研究

【作者】 杨浩；

【导师】 姚洁； 吴大建；

【作者基本信息】 南京师范大学 ， 光学工程（专业学位）， 2019， 硕士

【摘要】 表面等离激元与激子间的多元耦合在光与物质的相互作用的研究中扮演了重要角色,其基本的耦合原理及物理现象使得其在多模激光、多模传感等领域有着潜在价值。本文采用经典振子耦合理论和有限元数值仿真的方法研究了金属纳米阵列-J-聚合物-金属基底纳米结构中存在的多元耦合及其应用。首先证实一维金属阵列-J-聚合物-金属基底中存在表面等离激元极化激元(SPP)、局域表面等离激元(LSP)和J-聚合物分子激子间的强耦合,随之形成三个杂化模态。应用经典振子模型获得了杂化态中各原始模态的比重系数,并证实改变金属条宽度能够实现各个杂化模态中原始模态比重的调控。该工作对于非线性系统等离激元器件的设计和研发具有参考价值。在一维阵列的基础上,进一步证实二维金属阵列与J-聚合物和金属基底之间也存在类似的三元强耦合,同时二维金属阵列结构允许对入射光偏振态以及不同方向阵列周期进行调控,相较于一维金属阵列结构可调控的参量更多。除了改变纳米结构的几何尺寸,激子振荡强度受激子分子浓度影响,更方便调节,因此接下来研究了二维金属阵列-J-聚合物-金属基底结构中激子振荡强度对SPP-激子-LSP强耦合的影响,发现激子振荡强度越小,耦合形成的中间杂化模态的最大群速度也越小,这对于光捕获,信息储存以及增大光与物质间的相互作用有重要意义。主要研究内容及结果如下:(1)利用COMSOL仿真软件计算了一维金属阵列复合系统的光吸收谱,其谱线的变化反应了模态间的耦合作用。通过改变入射角和银纳米条宽度调控系统中LSP和SPP模式。首先在垂直入射的情况下改变银纳米条的宽度实现激子与LSP间的强耦合。然后在LSP与激子零失谐耦合的情况下通过增大入射角,在原有两元耦合的基础上引入SPP,实现SPP-激子-LSP三元强耦合,吸收光谱上可以看到两个明显的劈裂行为。三元耦合形成的三个混合模式,它们的色散行为与应用经典振子模型得到的结果一致。接着,在三元强耦合的基础上对LSP与激子失谐情况下的三元强耦合行为分析,发现当LSP具有比激子模态更大的能量,较高能级的杂化模态中激子成分被抑制,反之较低能级杂化态中激子成分被抑制。(2)与前面一维金属纳米阵列复合系统中实现SPP-激子-LSP耦合的研究方法相似,通过改变入射角实现二维金属阵列-J-聚合物层-银基底结构中的SPP-激子-LSP耦合,类似于一维结构中通过银纳米条的宽度调节LSP,这里由纳米柱直径变化调控LSP。在三元耦合形成的三个杂化模中,重点讨论能量位于中间的杂化模态的色散情况。该中间杂化模态的色散曲线始终被限制在LSP-激子耦合形成的劈裂带隙内,而该带隙的带宽是可以通过激子振荡强度来调控。激子振荡强度越大,该带隙的宽度也越大。基于以上讨论,我们计算了中间模态的群速度,发现群速度受到激子振荡强度的影响,激子振荡强度越小,其最大群速度越小,并且最大群速度位于该模态的中间。更多还原

【Abstract】 The multimode coupling among surface plasmons and exciton plays a significant role for light-matter interactions,The basic coupling principle and phenomenon make it valuable in multimode laser,multimode sensing and other fields.In this paper,the classical oscillator coupling theory and finite element numerical simulation method are used to study the multiple coupling and application of the metal nanoarrays-J-aggregates-metal substrates structure.Firstly,in the one-dimensional metal arrays structure,the multimode coupling among the local surface plasmon(LSP)excited by metal particles,the surface plasmon polaritons(SPP)excited by the metal grating and the molecular exciton is confirmed,and three plexcimon states are formed.The classic oscillator model is used to analyze the SPP-exciton-LSP coupling behavior and the weighting efficiencies of original modes in the three plexcimon states.It is proved that changing the width of metal strip can realize the regulation of the original modes weighting efficiencies in each hybrid modes.This work has important reference value for the design and development of the nonlinear systems.In addition,it is further confirmed that a similar strong ternary coupling exists in the two-dimensional metal arrays structure.The two-dimensional metal arrays structure allows the polarization state of incident light and the arrays periods in diferent direction to be regulated,which has more adjustable parameters.Compared with changing the geometric size of the nanostructure,the exciton oscillator strength is more easily regulated by the concentration of exciton molecules.Therefore,in the next step,the strong coupling of SPP-exciton-LSP is regulated by changing the exciton oscillation strength in the two-dimensional metal arrays structure.It is found that the smaller the exciton oscillation strength is,the smaller the maximum group velocity of the intermediate hybrid mode is,which is conducive to the design of information storage devices and increase the interaction between light and matter.The main research contents and results are as follows:(1)COMSOL software is used to calculate the optical absorption spectrum of the silver nanostrip arrays-J-aggregates-silver film nanostructure,the variation of absorption spectrum reflects the coupling between modes.In the nanostructure,LSP and SPP can be independently regulated by changing the incident Angle and the width of silver nanostrip,respectively.Firstly,in the case of nanostructure without J-aggregates,the strong coupling between SPP and LSP is achieved by changing the light incident Angle and obvious splitting behavior could be seen on the absorption spectrum.Then J-aggregate is added into the nanostructure,and the width of silver nanostrip is changed under the condition of light vertical incidence to achieve strong coupling between exciton and LSP.Finally,in the case of zero detuning coupling between LSP and exciton,SPP is introduced by changing the incident Angle to achieve the strong coupling among SPP,exciton and LSP.Two obvious splitting behaviors can be seen on the absorption spectrum,and these results are consistent with classic oscillator models.The coupling behavior is analyzed with the LSP-exciton detuning and found that if the LSP mode is tuned with higher energy than the exciton mode,the exciton composition in the high energy hybrid plexcimon mode is depressed,conversely,the excitonic composition in low energy hybrid plexcimon mode is suppressed.(2)Similar to the above research method,the SPP-exciton-LSP strong coupling of the silver nanocolumn arrays-J-aggregates-silver film nanostructure is realized by changing incident Angle,but the difference is that LSP is regulated by the diameter of the nanocolumn.We then discussed the dispersion of the middle hybrid plexcimon mode under different exciton oscillator strength.It is found that the dispersion of the middle hybrid plexcimon mode is always limited within the band gap formed by LSP-exciton strong coupling,and the bandwidth can be regulated by the exciton oscillator strength.Based on this,we discussed the coupling of SPP-exciton-LSP under different exciton oscillation strength,and found that the group velocity of the median hybrid plexcimon mode is affected by the exciton oscillation strength.The smaller the exciton oscillation strength is,the smaller the maximum group velocity is,and the maximum group velocity is located in the middle of this mode.更多还原