【作者】 郭丽娇；

【导师】 袁小聪；

【作者基本信息】 南开大学 ， 光学工程， 2013， 博士

【摘要】 光的基本性质中,频率、振幅、相位早已被深入研究并得到广泛应用。近些年,光的偏振性和对偏振态的调控成为了研究热点。对光场偏振态的调制,即刻意调制的非均匀偏振分布的矢量光束在光学系统以及光与物质相互作用等相关领域展现着独特的魅力。如径向偏振光紧聚焦后会出现强的纵向场,使其在光镊、光学存储、激光加工等领域发挥着重要的作用；径向偏振光激发的表面等离激元具有能量增强和局域的特点,使其在光学传感、拉曼增强、高分辨显微成像等领域扮演着重要的角色。然而,矢量光束的研究才刚起步,还存在许多未解决的科学和技术难题。本论文对矢量光束的生成和调控,及其在聚焦场整形和表面等离激元(Surface Plasmons Polaritons, SPPs)调控领域的应用进行了研究。主要内容如下：1.偏振可调矢量光束的生成。根据柱矢量光可由拓扑荷相反的右旋和左旋圆偏振光叠加而成的原理,我们用4-f干涉系统实现了偏振可调矢量光束的生成。由于引入特殊设计的相位型叉形光栅和Dammann光栅,与用空间光调制器或振幅光栅分束的干涉系统相比,该系统具有较高的能量利用率,且成本较低。通过在4-f系统的一路光中加入不同的相位片,可灵活产生柱矢量光和偏振混合矢量光；改变叉形光栅的拓扑荷,还可产生高阶矢量光,即用这种方法实现了偏振的调控,最后进行了实验验证。2.基于Richads-Wolf矢量衍射理论,分析了新型矢量光束,即偏振混合矢量光束和高阶矢量光束紧聚焦的特性。在此基础上,讨论了两种在聚焦场得到无衍射光的方法。第一种是径向偏振光经欧拉振幅调制得到无衍射光。分析表明,若考虑欧拉振幅透过率函数的权重因子,焦平面附近11λ范围内的能量分布更均匀,焦斑的能量半高全宽减小到0.535X,纵向分量所占比例达到71%。为了得到纵向分量占主要比例的亚波长无衍射光,我们提出了同时调制入射光偏振和振幅的新方法。用该方法得到的焦斑能量半高全宽为0.417λ,无衍射长度是径向偏振光的9.3倍,纵向分量所占的比例高达84%。两种方法各有优点,可满足不同的需要。3.通过对矢量光的偏振和相位进行调制,实现了SPPs光场的全光调控。根据聚焦结构激发SPPs与入射光偏振的关系,通过改变入射光中TE和TM偏振在光束横截面所占的比例及位置,SPPs焦斑会被拉伸或出现多个SPPs焦斑；同时,我们对这种偏振调制SPPs的方法进行了实验验证。最后,对矢量光束进行螺旋相位调制,实现了SPPs焦斑位置的移动,随着螺旋相位拓扑荷的增加SPPs焦斑移动的范围在增大。这种全光调控SPPs的方法仅需调制入射光的偏振和相位分布就可在金属薄膜表面实现SPPs光场的调控,具有易于实现和灵活调控的优点,在相位型差分干涉传感和纳米光子器件集成领域有着潜在的应用价值。更多还原

【Abstract】 The characters of light involving the amplitude, phase and frequency have been deeply studied and widely used in various fields. In recent years, the polarization state of light and its manipulation have attracted much attention. Spatially arranging the polarization state of a light beam, purposefully and carefully, is expected to lead new phenomena and applications. One example is radially polarized (RP) vector beam, which has cylindrical symmetry polarization in beam’s cross section. RP beam has a strong longitudinal field when focused by a high NA lens, which makes it the optimal polarization choice in various applications, such as particle trapping, second harmonic generation, optical data storage, laser cutting and surface plasmon excitation. Currently the research on vector beams is fresh and there remain many scientific and technological problems. Thus, this dissertation is focus on the generation and manipulation of vector beams, and the applications in focus shaping and surface plasmon poariton (SPPs) manipulation.The main contributions of this dissertation are as follows:1. A method of generating novel vector beams is proposed. Based on the principle that a general cylindrical vector beam is the superposition of a positive vortex encoded right circularly polarized beam and a negative vortex encoded left circularly polarized beam, we use a4-f interferometric system to generate vector beams. In this system, a special designed vortex phase grating and a Damman phase grating are used, which makes it higher energy conversion efficiency than the hologram reconstructed either by an SLM or amplitude-modulated diffractive elements. By introducing a special phase plate in one arm of the interferometer, hybride polarization states of the vector beam can be obtained accordingly. When the topological charge of the vortex phase grating is changed, vector beams with charge can be generated as well. This method shows higher energy conversion efficiency and easier polarization conversion for the vector beams.2. Based on the Richads-Wolf vecor diffraction theory, we analysis the focusing property of vector beams with hybride polarization states and with high topotogical charge. Then two methods for focal field shaping are discussed. The first method is using the Eular transmission function to modulate amplitude distribution of RP beams. We find that by introducing a group of optimized constant factors for the Eular amplitude transmission function, the depth of the focal field (DOF) is enlarged to11λ, the focal spot is reduced to0.535X, and the ratio of longitudinal field to total field is increased to71%. In order to maintain the long DOF and reduce the size of focal spot, we study the second method of both polarization and amplitude modulation for incident beams. By this method, a subwavelength focal spot (0.4171) with long DOF is achieved, and the ratio of longitudinal field to total field is as high as84%.3. By analysis the property of surface palsmon excitated by focused vector beams with hybride polarization states, we propose an all-optical method to localize and cotntrol the SPPs electric field distribution. Calculation results show that, SPPs focal spot can be elonged and splited into focal spot array when change the area ratio of the TE to TM polarization in the incident beam’s cross section. When the vector beam with different topological charge m is focused on the metal surface, focal spot array also can be achieved, and the relationship between the topological charge m and the number of SPPs focal spots is described by2(m-1). Meawhile, the method of polarization manipulation of the SPPs is confirmed in experiment. At last, we realize all-optical dynamic control of SPPs focal spot by combining the vortex phase with RP vector beams, and.find moving distance of the SPPs spot is enlarged when increasing the topological charge of the vortex phase. Compared to manipulation by metal nano-structures, the all-optical manupulation of SPPs has the advanteges of easy implementation and flexible control, leads to potential applications in phase-SPR biosensor and integrated nanophotonic device.更多还原