超快等离激元动力学及其控制

发布时间：2018-05-02 01:23

本文选题：超快表面等离激元 + 局域近场增强　；参考：《长春理工大学》2017年博士论文

【摘要】：超快表面等离激元由于具有亚波长局域、局域近场增强等独特的性质,使人们能够在飞秒时间、纳米空间尺度上操纵和控制光子,为实现全光集成,发展更小、更快和更高效的新型纳米光子学器件提供了一条有效的途径。它在光计算、光存储、光催化、纳米集成光子学、光学传感、生物标记、医学成像、太阳能电池以及表面增强拉曼光谱等领域有着重要的应用,因而受到物理学、材料科学、纳米科技等领域研究人员的极大关注。基于超快表面等离激元的独特性质,本文利用干涉时间分辨光辐射电子显微(Interferometric time-resolved photoemission electron microscopy,ITR-PEEM)技术,重点对超快激光辐照金属纳米结构产生的超快等离激元局域近场进行成像研究,实现了极小时空尺度等离激元的动力学时间演化过程的成像及其控制。本论文的主要工作和成果如下:首先,利用ITR-PEEM技术对p偏振7 fs脉冲宽度激光作用蝶形纳米结构以及纳米线形成的超快等离激元场(热点)的动力学过程进行了成像。结果表明,当两束脉冲的相对时间延时小于13 fs,受激光干涉场的主导,蝶形纳米结构中右纳米三角左尖端以及左纳米三角的下外角两位置的等离激元以相同的频率振荡。其后,两位置处等离激元的振荡频率发生变化,逐渐移向其自身的本征频率。对于不同偏振方向的飞秒光激发蝶形纳米结构形成的热点,其各自的等离激元振荡频率、动力学时间演化过程均不相同。入射激光的偏振方向与p偏振之间的最小夹角越大,所激发的等离激元振荡频率越快。由于被激发等离激元的相位传播,纳米线不同位置处形成等离激元的动力学时间演化曲线从第二个光学周期开始出现相位差。此外,对不同尺寸纳米线相对应位置的等离激元动力学过程进行了研究。实验结果表明,时间演化曲线中存在的相位差归因于等离激元的相位传播以及等离激元振荡频率不同。其次,对p偏振7 fs光脉冲激发不同尺寸的石门纳米结构产生的热点分布进行了成像研究,以及对不同位置产生等离激元的动力学过程进行了研究。实验结果表明,使用p偏振7 fs光脉冲激发石门纳米结构,观察到热点主要集中在二聚体的左端。同时,二聚体上棒的右端以及单竖棒的上端观察到了因样品缺陷引起的热点。在二聚体长度相等的较大尺寸石门结构中(二聚体中棒的长度均为220nm,单体竖棒的长度为500 nm),发现二聚体左端两位置对应的等离激元模式具有相同的共振频率,且两位置的等离激元振荡具有相同相位。在该样品形成的等离激元的动力学演化研究中,观察到了因多模式等离激元的相干叠加而产生的拍频现象,其在时间演化曲线中呈现为紧挨主峰侧翼的出现。在二聚体长度相等的较小尺寸石门结构中(二聚体中棒的长度均为220 nm,单体竖棒的长度为300 nm),除了具有二聚体长度相等的较大尺寸石门结构的所有特征外,我们还观察到了相邻较近的两个随机缺陷对应的等离激元的动力学相互影响行为,发现两者以同位相振荡,其归因于相邻较近的等离激元出现强耦合所致。此外,当两束7fs光脉冲间的延时从11.35 fs变化为12.68 fs时,较高的光电子产额可以被控制从二聚体上棒的左端变化到右端;如果两脉冲的延时进一步增加,较高光电子产额又回到棒左端的位置。这说明通过改变两束光脉冲间的延时,可对石门结构中形成的纳米等离激元场的空间分布进行阿秒时间精度的相干控制。在二聚体长度不相等的石门结构中(二聚体中棒的长度分别为220 nm与120 nm),观察到了其左端两位置对应等离激元模式的共振频率有差异,等离激元的振荡随时间演化出现完全失相。接下来,开展了波长为400 nm的超快光脉冲激发银方块形结构产生等离激元场的控制研究。结果表明,不同偏振方向的线偏振激光照射下,银方块形结构热点的分布位置及其强度发生改变。特别是发现当激光的偏振方向变化90°时,热点从银方块形结构的上侧棱边区域调控到下侧棱边区域。通过改变入射线偏激光的偏振方向,对银方块形微米结构中超快等离激元实现了主动控制。最后,开展了通过改变中心波长为800 nm的单光束飞秒脉冲偏振方向和改变两束飞秒光脉冲延时的方法对等离激元场分布进行控制的研究。当单束入射飞秒激光的偏振方向从30°旋转到120°时,蝶形纳米结构的热点从左纳米三角形的下外角变化到其上外角,实现了蝶形纳米结构热点分布的控制。当两束正交飞秒激光脉冲间的延时变化步长为0.67 fs时,热点在蝶形的三角形中的位置分布已发生明显的变化。特别是,两脉冲的相对延时从-0.67 fs变化为0.67 fs,蝶形纳米结构的热点从左纳米三角的下外角完全移动到了其上外角位置。采用FDTD方法对以上工作进行模拟研究,结果表明模拟结果与实验观察到的现象完全吻合。当两束非正交飞秒激光脉冲(一束为p偏振,另一束相对p偏振逆时针旋转60°)的相对延时从0.67 fs变化为1.33 fs时,蝶形纳米结构的热点从左纳米三角的上外角变化到了其下腰位置。这说明通过改变两束飞秒光脉冲延时的方法,实现了超快等离激元在纳米空间尺度、阿秒时间精度的相干控制。本论文的研究工作为全面揭示出极小时空尺度等离激元的独特性质,深入掌握其表征以及控制技术,实现对极小时空尺度等离激元在阿秒时间精度、纳米空间分辨率的全貌揭示打下了坚实的基础,对于发展以等离激元为基础的新型光电器件具有重要的意义。
[Abstract]:The ultrafast surface plasmon, due to its unique properties such as subwavelength localization and local near-field enhancement, enables people to manipulate and control photons at femtosecond time and in nanoscale scales. It provides an effective way to achieve all-optical integration and develop smaller, faster and more efficient new nanoscale devices. Storage, photocatalysis, nanoscale photonics, optical sensing, biomarkers, medical imaging, solar cells and surface enhanced Raman spectroscopy have important applications, which have attracted great attention by researchers in the fields of physics, material science, nanotechnology and other fields. Based on the unique properties of ultrafast surface plasmons, this paper uses interference. The time resolved Interferometric time-resolved photoemission electron microscopy (ITR-PEEM) technology, focusing on the imaging research on the ultrafast laser irradiated metal nanostructures produced by the ultrafast plasmon polaritons near field, has realized the imaging of the dynamic time evolution process of the tiny space-time polaritons. The main work and results of this paper are as follows: first, the ITR-PEEM technique is used to imaging the dynamic process of the p polarization 7 fs pulse width laser on the sphenoidal nanowire and the ultrafast plasmon field (hot spot) formed by the nanowires. The results show that the relative time delay of the two pulses is less than 13 FS and is subjected to the laser interference field. The same frequency oscillates in the two position of the right nano triangle and the lower outer corner of the left nano triangle in the butterfly nanoscale structure. Then, the oscillation frequency of the plasmon at the two position changes and gradually moves to its intrinsic frequency. The dynamic time evolution process of their respective plasmon oscillations is different. The greater the minimum angle between the polarization direction of the incident laser and the p polarization, the faster the oscillation frequency of the excited element excites. The dynamic time of the nanowires is formed at different positions due to the phase propagation of the excitations. The phase difference of the evolution curve begins from second optical cycles. In addition, the kinetic process of the equivalent ionization of the nanowires with different sizes is studied. The experimental results show that the phase difference in the time evolution curve is attributed to the phase propagation of the equal ionization excitations and the difference in the oscillation frequency of the plasmon. Secondly, the polarization of the P is 7. The FS optical pulse stimulated the distribution of hot spots in different sizes of Shimen nanostructures, and studied the kinetic process of the plasmon polaritons produced in different locations. The experimental results showed that the p polarization 7 FS light pulses were used to stimulate the Shimen nanostructure, and the heat point was mainly concentrated on the left end of the two polymer. At the same time, two polymerization was found. The hot spots caused by sample defects are observed on the right end of the rod and the upper end of the single vertical rod. In the large size Shimen structure with equal length of two polymer (the length of the rod in the two polymer is 220nm, the length of the single rod is 500 nm), it is found that the equivalent resonance frequency of the equi excitation mode corresponding to the two position of the two polymer left end has the same resonance frequency, and two In the study of the kinetic evolution of the plasmons formed by the sample, the frequency of the beat frequency caused by the coherent superposition of the multimode plasmon is observed, and it appears in the time evolution curve as the appearance of the main peak side of the main peak. The smaller size of the Shimen structure with equal length of the two polymer is the same. In the two polymer, the length of the rod is 220 nm and the length of the single rod is 300 nm. In addition to all the characteristics of the large size Shimen structure with equal length of two polymer, we also observe the dynamic interaction of the equitor plasmons corresponding to the adjacent two random defects, and find that the two are in the same phase oscillation, and their attribution is attributed. In addition, when the time delay between two beam 7FS pulses varies from 11.35 fs to 12.68 FS, the higher photoelectron output can be controlled from the left end of the two polymer rod to the right end; if the delay of the two pulse increases further, the higher photoelectron yield is back to the left end of the rod. By changing the delay between two beams of light pulses, the spatial distribution of the nanoscale plasmon field formed in the Shimen structure can be coherently controlled by the time precision. In the Shimen structure with two polymer lengths (the length of the rod in the two polymer is 220 nm and 120 nm respectively), the corresponding plasmon modes at the left end in the two position are observed. The resonance frequencies are different, and the oscillations of the plasmon are completely deformed with the time evolution. Next, the control study of the excited element field of the silver square block excited by the ultra fast light pulse with a wavelength of 400 nm is carried out. The results show that the distribution position of the hot spot of the silver square block structure under the linear polarization laser irradiation with different polarization directions and the distribution of the hot spot of the silver square block structure is shown. Its intensity changes. Especially, when the polarization direction of the laser is changed to 90 degrees, the hot spot is regulated from the upper edge edge region of the silver square block to the lower edge edge region. By changing the polarization direction of the laser polarized laser, the active control is realized for the ultra fast plasmon in the silver square microstructure. Finally, the change is carried out. The polarization direction of the single beam femtosecond pulse with a wavelength of 800 nm and the method of changing the delay of two femtosecond light pulses are controlled. When the polarization direction of the single beam incident femtosecond laser rotates from 30 to 120 degrees, the hot spots of the butterfly nanoscale change from the lower outer corner of the left nanoscale triangle to the upper outer corner. The distribution of hot spots in the butterfly shaped nanostructures is now controlled. When the delay variation step between two beams of two beam quadrature femtosecond laser pulses is 0.67 FS, the position distribution of the hot spots in the butterfly shaped triangle has changed obviously. In particular, the relative delay of the two pulses varies from -0.67 fs to 0.67 FS, and the hot spots of the butterfly shaped nanostructures are from the left nanometer triangle. The lower and outer corners are completely moved to its upper and outer corners. The FDTD method is used to simulate the above work. The results show that the simulation results are in perfect agreement with the observed phenomena. The relative delay of the two beams of two beam non orthogonal femtosecond laser pulses (one beam for p polarization and 60 degrees against the p polarization counter clockwise rotation) varies from 0.67 fs to 1.33 FS The focus of the sphenoidal nanostructure changes from the upper and outer corners of the left nanoscale triangle to its lower waist. This shows that the time-delay of the two beams of femtosecond light pulses is changed to realize the coherent control of the time precision of the ultrafast plasmons at the nanoscale scale and the time precision of the attosecond. The unique character of the element and the deep grasp of its characterization and control technology have laid a solid foundation for the full appearance of the nanosecond time precision and nanoscale resolution, which is of great importance to the development of the new optoelectronic devices based on the plasmons.

【学位授予单位】：长春理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TN15;O441

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