【作者】 李雪璁；

【导师】 孙秀冬；

【作者基本信息】 哈尔滨工业大学 ， 光学， 2010， 博士

【摘要】 光镊是利用高度聚焦的激光微束形成的光学梯度力势阱来实现对微纳量级粒子的捕获与操控的技术,它所产生的皮牛量级的力正好适用于操控微纳量级的粒子。随着光镊技术的发展,它已经广泛应用在物理学、生物医学、化学以及精密加工等领域。随着这些领域的发展,人们对光学捕获和操控的效率、范围和精度等不断提出新的要求。本论文就是以满足这些新要求为目标,对粒子的精确定向操控、角向操控,以及多粒子的集体操控和分立操控等进行了相关研究,并引入新的捕获光模式,优化光镊系统性能。聚焦光斑形状和偏振状态是影响粒子定向操控的主要因素,本论文通过调整聚焦光斑形状和捕获光偏振态实现了三维方向上对粒子的定向操控,尤其是对生物粒子的定向操控。圆形光斑可以操控圆柱状粒子(生物粒子大肠杆菌和碳纳米管)使其完成竖直取向,而线形光斑可以操控圆柱状粒子使其水平取向。对于具有电学各向异性的粒子而言,如碳纳米管,其在光阱中的取向还受线偏振方向的影响。通过调节线偏振方向,能够按特定方式排列多根碳纳米管,使其沉积在衬底上并组装成固定结构。此外,利用激光携带能量这一特点,还成功地实现了对菲醌(PQ)的诱导定向生长。通过引入不同捕获光,改变捕获光强度分布等方法研究捕获光性质对光镊性能的影响。本论文利用液晶偏振转换器实现了两种具有特殊偏振和强度分布的柱矢量光束——方位角偏振光束和径向偏振光束,从理论和实验上分析了它们的聚焦特性。方位角偏振光束聚焦后整个聚焦场都是横向分布,轴上光强为零,形成中空环形光斑;而径向偏振光束则形成实心聚焦光斑,其尺寸小于一般高斯光束的聚焦光斑。将方位角偏振光束、径向偏振光束和高斯光束作为捕获光引入光镊系统,首次搭建了捕获模式间可互相切换的新型三模式光镊系统,分别测量了三种捕获模式下光镊系统的轴向和横向捕获效率。实验结果显示:径向偏振捕获光的轴向捕获效率依次大于方位角偏振光束和高斯光束,而横向捕获效率刚好相反,高斯捕获光带来的横向捕获效率依次大于方位角偏振光束和径向偏振光束。基于方位角偏振光束中空环形聚焦光斑的独特性,利用方位角偏振捕获光束分别实现了微米量级金属粒子的稳定捕获和对粒子位置的精细调控,扩大了光镊操控粒子的范围以及控制粒子的精度,并证明了方位角偏振捕获光的使用可以有效减少光镊对所操控粒子的热损伤。利用光束的角动量实现了对粒子的角向操控,并研究了引起光致旋转的机理及影响旋转速度的因素。自旋角动量引起的光致旋转可以使粒子获得较高的转速,通过调控激光功率可以控制粒子的旋转速度,溶液粘滞系数和粒子的几何尺寸也是影响旋转速度的重要因素。而轨道角动量引起的光致旋转则可以带动多粒子共同旋转。随后,我们提出了利用主动粒子带动从动粒子旋转和定向的新方法,并成功运用该方法实现了生物粒子大肠杆菌和碳纳米管的旋转。此外,根据其中一种主动粒子Rubrene微粒特有的荧光性质,提出了分选和操控其他荧光微粒的构想。采用传统单光阱光镊系统实现了微米量级和纳米量级多粒子的集体捕获和操控,其中纳米粒子的聚集数量的动态变化过程是由粒子极性和热扩散情况决定的。此外还实现了多个粒子的聚集翻转。提出利用棱镜对生成一维光束阵列(包括一维中空光束阵列和一维线形阵列)的简单、廉价的实验方法,并利用其作为光源构建了新型的多光阱光镊系统,初步实现了多粒子的分立捕获和操控。更多还原

【Abstract】 Optical tweezers are the beam gradient optical traps where micro particles could be trapped by focusing the laser beam using a microscope objective. The gradient force generated by optical tweezers is suitable to trap and manipulate micro- and nano- particles. Optical tweezers had become a versatile tool for researches in many science fields including physics, biomedicine, and fine machining. With the development of these fields, there are new needs to optical tweezers technique. In this thesis, we realized the orientation and angular manipulation of particles, the collective and separate manipulation of multi-particle to meet these increasing requests. We also had introduced new trapping beam mode to optimize system performance.The shape of the optical trap and the polarization of the laser are important factors for the orientating manipulation of particles. Orientating manipulation of particles especially biological particles were performed in three-dimension by optical tweezers. Vertical and horizontal manipulations of cylindrical particles (Escherichia coli and carbon nanotubes) were achieved by dot-shaped and line-shaped optical trap. The particles with the anisotropic electric characters such as carbon nanotubes (CNTs) could be orientated by linear polarized optical trap. CNTs could be oriented and assembled in the two-dimensional plane by controlling the polarization direction. By using of the highly focused heat energy at the optical trap, orientating grown of phenanthrenequinone (PQ) was realized successfully by optical tweezers.The properties of trapping beam are the main factor which influencing the system performance of optical tweezers. Cylindrical-vector beams including azimuthally polarized beam and radially polarized beam were formed by the liquid-crystal polarization converter. The intensity distribution near the focal region of these beams were calculated and analyzed theoretically and then verified experimentally. The azimuthally polarized beam is distinguished by a purely transverse annular focal region, and the radially polarized beam is distinguished by its longitudinal field at high numerical apertures. The focus spot size of radially polarized beam is smaller than the focused Gauss beam. We had constructed a new three-mode optical tweezers system, which consisted of the azimuthally polarized trapping beam, the radially polarized trapping beam, and the Gauss trapping beam. The radial and axial trapping efficiency were measured under these three trapping modes, respectively. In axial direction, the radially polarized trapping beam resulted in the best trapping, followed by azimuthally polarized trapping beam and Gauss trapping beam in the order. On the contrary, the Gauss trapping beam resulted in the best trapping in radial direction. Due to the unique hollow focus spot, the stable trapping of metallic particles and fine controlling of particles were demonstrated by azimuthally polarized trapping beam. In addition, azimuthally polarized trapping beam could improve the trapping effect while reducing the risk heat damage.Angular manipulations of particles were achieved by optical tweezers due to the transfer of angular momentum from light to particles. We had discussed the principle of the light-induced rotation caused by spin angular manipulation. The results showed that the rotation speed depended on the incident laser power, the size and the rotational symmetry of the particles. The rotation speed of particles induced by spin angular momentum of light was higher than that caused by orbital angular momentum. And optical rotation induced by orbital angular momentum could promote multi-particle co-rotating. Then we had proposed a novel method to rotate driven particles via combining it with drive particles. Most importantly, there were no special requirements for the shape of the driven particles. The biological particle (E. coli) and CNTs can be continuous rotated by optical tweezers using this method. Moreover, the Rubrene particles could emit strong fluorescence exciting by the laser at the wavelength of 532nm, and it could provide a potential application to sort and manipulate other particles with the fluorescence characteristics.The collective trapping and manipulation of micro- and nano- multi-particle were achieved by traditional single optical trap system. The molecular polarization and thermal diffusion of nanoparticles played crucial roles in the light-induced agglomeration and diffusion process. Moreover, we had proposed a simple and inexpensive method to achieve one-dimension beam array including Gauss beam, hollow core beam and line-shape beam using a couple of prisms. A novel multi-trap optical tweezers system was constructed by inserting a couple of prisms based on the previous traditional optical tweezers system. The separate optical trapping and manipulation of multi-particle were achieved preliminary by this new system.更多还原