离轴深聚焦光束激发的SPPs自干涉场特性研究

发布时间：2018-03-15 17:22

本文选题：表面等离子体极元　切入点：自干涉　出处：《南昌航空大学》2015年硕士论文　论文类型：学位论文

【摘要】：表面等离子体极元(Surface Plasmon Polaritons,SPPs)是在金属表面激发的电磁波,具有近场增强、亚波长局域和异常色散等特点,可以在亚波长尺度对光子进行操纵,已经在各个领域得到广泛的应用。由于传统光学器件中存在一个经典光学无法逾越的衍射极限,使得现有的光学仪器分辨率很难进一步提高,光电器件无法实现更高程度的集成。表面等离子体极元为解决这一问题提供了一个重要的突破口。另外,基于近轴原理而设计的光学仪器中,入射光束的近轴性是保证成像质量的重要条件。光束的离轴会造成像差等问题,大大降低仪器的成像分辨能力。光束的离轴直接影响着SPPs的应用效果,弄清离轴光激发SPPs光场的特性有重要的理论和实践意义。正入射深聚焦光激发的SPPs具有对称和计算简便等优点。当光束偏离光轴,聚焦区域的波矢分布将发生整体的改变,造成透射场的畸变、强度和对比度下降等一系列问题。本文对离轴光束激发SPPs的产生机理和分布规律等特性做了详细的理论分析和模拟仿真,揭示了离轴光激发SPPs的一些基本规律。在理论计算中,本文采用了角谱分析方法;在模拟仿真中,本文采用了基于时域有限差分方法的商业计算软件FDTD Solutions.本文首次提出了“临界离轴角”和“等效数值孔径”的概念。透射场强度分布受到纵向共振分量的调制,离轴角越大,调制作用越弱,并且存在一个理论临界离轴角,实际的临界离轴角小于理论值。在线性偏振光入射的条件下,当光束倾斜方向平行或垂直于偏振方向时,SPPs自干涉场仍然是轴对称的,但只有一条对称轴。入射光垂直于偏振方向倾斜会改变聚焦光场的S波和P波成分,降低SPPs的激发效率。在同一角度下,倾斜激发的效率比离轴激发要高。光束的倾斜或离轴入射实际上是减小了共振成分对整个透射场的调制作用,使仪器成像分辨率下降。本文角谱计算与FDTD仿真的光场分布基本相同,但FDTD仿真的光场条纹对比度更高。两种方法的计算结果MSE都不超过0.02,因此,本文推导的光场角谱公式基本合理。
[Abstract]:Surface Plasmon Polaritons (SPPs) is an electromagnetic wave excited on a metal surface. It has the characteristics of near-field enhancement, sub-wavelength localization and anomalous dispersion, so it can manipulate photons at sub-wavelength scale. It has been widely used in various fields. Due to the existence of a diffraction limit which can not be exceeded by classical optics, it is difficult to improve the resolution of existing optical instruments. Optoelectronic devices cannot achieve a higher degree of integration. Surface plasma polar elements provide an important breakthrough to solve this problem. In addition, in optical instruments designed based on the principle of near axis, The paraxial property of the incident beam is an important condition to ensure the imaging quality. The off-axis of the beam will lead to aberration, which greatly reduces the imaging resolution of the instrument. The off-axis of the beam directly affects the application effect of SPPs. It is of great theoretical and practical significance to understand the characteristics of the SPPs field excited by off-axis light. The SPPs excited by the normal incident deep focusing light has the advantages of symmetry and simplicity of calculation. When the beam deviates from the optical axis, the wave vector distribution in the focusing region will change as a whole. A series of problems such as distortion of transmission field, decrease of intensity and contrast, etc. In this paper, the mechanism and distribution of SPPs excited by off-axis beam are analyzed and simulated in detail. Some basic laws of off-axis photoexcitation SPPs are revealed. In theoretical calculation, the angular spectrum analysis method is used, and in the simulation, In this paper, the commercial computing software FDTD solutions based on finite-difference time-domain method is used. The concepts of "critical off-axis angle" and "equivalent numerical aperture" are proposed for the first time. The intensity distribution of the transmission field is modulated by the longitudinal resonance component, and the off-axis angle increases. The weaker the modulation action is, and the existence of a theoretical critical off-axis angle, the actual critical off-axis angle is smaller than the theoretical value. When the beam tilting direction is parallel or perpendicular to the polarization direction, the SPPs self-interference field is still axisymmetric, but there is only one symmetry axis. The S wave and P wave composition of the focused light field will be changed when the incident light tilts perpendicular to the polarization direction. Reducing the excitation efficiency of SPPs. At the same angle, the efficiency of inclined excitation is higher than that of off-axis excitation. The tilt or off-axis incidence of the beam actually reduces the modulation effect of resonance components on the whole transmission field. The optical field distribution of this paper is basically the same as that of FDTD simulation, but the contrast of light field fringes in FDTD simulation is higher. The calculated results of both methods are less than 0.02, so, The formula of angular spectrum of light field derived in this paper is basically reasonable.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O436.1;O441.4

【相似文献】