【作者】 杨阳；

【导师】 臧维平；

【作者基本信息】 南开大学 ， 凝聚态物理， 2013， 博士

【摘要】 随着科学技术日新月异的发展,以激光为基础的光镊技术受到了国内外研究学者的广泛关注。自从Ashkin等首次从实验上证明了光对小球具有俘获作用,并将其应用于对小球的操控与捕获,光镊技术便蓬勃发展起来,并已成为纳米技术、生命科学技术等微粒操控领域的重要研究手段。光镊技术的优点是可以实现无机械损伤,无污染、无损伤的微粒操控,这对于活体生物粒子也是适用的。使用一个中等强度的聚焦光束,就可以对尺寸从几个纳米到几个微米的中性粒子实现加速、减速甚至是捕获。物理学家们已经分别从理论和实验上研究了平面波,紧聚焦高斯光束等传统光束对微观粒子的操控与捕获。最近发现的艾利光束,由于其无衍射传播,横向加速以及自我愈合的优良特性,可以很好地应用到传统的光镊技术中。可将微粒实现长距离的甚至弯曲路径的传输。在本文中,通过电磁场的矢势表示以及傅立叶变换的角谱方法,我们分析了一维和二维艾利光束透过平面界分面后的传播情况,以及当入射角大于临界角时,界面上方由于全反射产生的艾利光束消失场。理论结果表明,艾利光束消逝场随着透射距离的增加,很快地衰减。通过洛伦兹-米氏理论,我们分析了不同介质的小球对艾利光束消逝场的散射以及小球受到的光辐照力,并模拟了小球在艾利光束透射场中的运动轨迹。数值结果表明,随着艾利光束中心位置的变化,光辐照力曲线呈现出与消逝场分布相对应的振荡。随着小球半径的增加,不同介质的小球会产生不同的形态依赖共振(MDR)。并且其振荡形态与球内电磁场分布密切相关。同样,我们根据球内电磁场的分布分析了艾利光束光镊力的MDR共振峰的形态。我们发现当入射波为艾利光束的消逝波时,其光镊力的MDR曲线振荡峰的品质因子Q要远大于透射波对应的共振峰的Q值。并且共振时球内的电磁场的环状分布随着艾利光束消逝场的入射角以及透射距离的变化结构有很大的改变。大量的数值结果表明,球内电磁波的干涉影响着其相应的MDR共振峰的形态,具体为：环状分布的行波模式对应于高Q值,低背底的共振峰,而强干涉的驻波模式对应于低Q值,高背底的共振峰。并且,干涉越强,Q值越低,背底越高。我们分析了透射过分界面的消逝波在小球和界面之间的多重散射对光辐照力以及电磁场分布的影响。结果表明,多重反射在光束能量集中分布的地方影响较大。我们还分析了金属界面时,表面等离激元共振(SPP)对艾利光束消逝场的影响。数值结果表明,当产生SPP共振时,艾利光束消逝场场强约可增强一个数量级,消逝场的分布更加局域化,相应的光镊力可增加两个数量级。更多还原

【Abstract】 With the never-ending changes and improvements of science and technology, more and more attention has been paid into the optical tweezers based on laser technology. Since Ashkin et al. proved that three-dimensional trapping of a dielectric particle is possible by use of a single, highly focused laser beam [1], optical tweezers have become an indispensable tool for manipulating small particles. Currently optical tweezers have found numerous applications in the fields of biology, chemistry, and physics. Optical tweezers are sub-contact, pollution-free and noninvasive, then can be used to manipulate live cells. That is to say using a tightly focused beam, we can accelerate, decelerate, even trap nanoparticles and microparticles. Physicists have studied optical trapping and manipulation of microscopic particles with traditional plane wave and focused Gaussian beam theoretically and experimentally. Recently, the experimental realization of Airy beam, can be well applied into the conventional optical tweezers, which can avoid divergence and diffraction within a certain propagating distance for its unique features:"non-diffracting", transverse acceleration and self-healing properties.In this article, using vector potential and Fourier transform spectrum representation, we investigate the one-and two-dimensional Airy beam propagating through an interface. And the Airy evanescent field in the upper medium formed by total internal reflection when the incident angle is larger than the critical angle. Numerical results show that the Airy evanescent wave dies away several wavelengths away from the interface. Utilizing the generalized Lorenz-Mie theory, we investigate the scattering of the Airy evanescent field by a spherical dielectric particle, the optical forces exerted on the Mie particle, and simulate the motion trajectory of the particle. Numerical results show that the optical forces exhibit strong oscillations which are corresponding to the distributions of the evanescent field. With the increasing the size of particle radius, Morphology Dependent Resonance (MDR) occurs for the particle with specific refractive index.Morphology-dependent resonance (MDR) of the optical forces for a particle illuminated by Airy beams is investigated with respect to its internal field distribution. We find the quality factor Q of the resonant peaks for a damped wave is much larger than that for a propagating wave. The ring structures arising from the resonance transform significantly with the parametric evolution of Airy evanescent wave, and the interference of the internal waves have a great impact on the Q factor and the background of the resonant peak, e.g., travelling wave patterns correspond to high Q peaks, while strong interference patterns for high background peaks. But the key structure of the internal field for the Airy transmitted wave won’t change.The multiple reflections of the evanescent wave between the particle and the interface are also investigated, which show significant impacts on the region where the energy concentrate in. We also analyzed the enhancing of the Airy evanescent wave by the surface plasmon resonance (SPP) the metal film covered on the interface. Numerical results show that when SPP resonance occurs, the intensity of the Airy evanescent field is enhanced by one order of magnitude, the distribution of the evanescent field is localized, the corresponding optical force increases two orders of magnitude.更多还原