小型化可调光镊设计

光镊利用强会聚激光对微粒产生的梯度力来捕获微粒,可以进行无损、远程操控,同时具有皮牛精度的测力特性,已经成为物理学、生命科学和胶体化学等研究领域中不可缺少的研究工具。光镊效应可以表现微小的光子动量和角动量,是物理学的重要教学工具。本文根据高斯光束传播和变换规律,设计具有稳定捕获性能的最小化光镊,并给出了典型参数。光镊系统由捕获激光、光束耦合系统、倒置生物显微镜和大数值孔径物镜组成,成像系统由物镜、摄影目镜和CCD相机组成。本光镊系统具有紧凑特性,同时通过保持物镜后瞳充满度来实现稳定捕获。在该最小光镊系统上,可以根据用户需求增加光镊阱位操控系统、刚度调节系统和其他辅助设备以满足不同操控要求,可以很好地满足科研和教学需求。     

飞秒光镊技术及其发展

激光捕获技术是利用光辐射力来捕捉、移动和操纵微粒的先进技术。飞秒光镊在实现粒子微纳操纵的同时还伴随着非线性现象的发生。阐述了飞秒光镊的模型和原理以及系统的各种结构形式,包括单光束梯度力光阱、贝塞耳光阱、双光束光纤光阱和冲击波光阱几种形式,并分析了每种形式的特点。     

飞秒激光光镊横向光学力的理论分析

旨在将飞秒激光脉冲序列视为对连续光的周期抽样结果,分析飞秒激光脉冲序列作为光镊光源捕获电介质微粒时产生的横向光学力,并给出受光微粒所受横向光学势阱力的理论模型及计算公式.数值计算结果表明,飞秒激光脉冲所产生的横向光学力能抵消由于布朗运动引起的微粒中心偏移的影响,实现对微粒的稳定束缚.     

光镊轴向阱位操控及器件安装误差对径向阱位操控的影响

光镊利用光学梯度力捕获和操控微小粒子,已经成为深入研究生物分子间相互作用等微观机制的独特技术.光镊光束操控系统一般由扩束输入镜、扩束输出镜、调焦透镜、耦合透镜和压电转镜等光学元器件组成,以保证物镜后瞳充满的前提下实现光镊阱位操控.光镊阱位的三维精确操控是实现光镊位钳和力钳模式的基本条件.本文根据矩阵光学,对基于无穷远校正显微镜的光镊操控光路进行计算,分析扩束输入镜、调焦透镜和物镜轴向位置调整,以及压电转镜、调焦透镜和耦合透镜安装位置误差对光镊径向阱位操控精度的影响,得到了物镜高度调整基本不会影响光镊径向位置操控,压电转镜和调焦透镜的安装位置误差对光镊径向阱位操控精度影响最大等结论,提出了能够实现径向阱位精确操控的轴向阱位动态操控范围,为光镊设计和操控提供理论和实验指导.     

时域有限差分法数值仿真单光镊中微球受到的光阱力

本文采用三维时域有限差分法(FDTD)和Maxwell应力张量法建立了单光镊在焦点附近俘获球形微粒的光阱力模型,采用基于球矢量波函数(VSWF)的五阶高斯光源作为仿真光源,得到了准确的光场传播.讨论了光源的波长、束腰、偏振态和微球的半径、折射率对光阱力的影响,分析了在单光镊俘获微球时,邻近微球对光阱力的影响.特别研究了光源的偏振态对微球所受光阱力的作用效果,仿真结果表明圆偏振光比线偏振光对微球的俘获力更大;被光镊稳定俘获的微球,会受到邻近微球干扰,失去平衡状态,改变光源的偏振态可以改变微球的受力状态. 关键词： 光镊 光阱力 介质微球 时域有限差分法(FDTD)     

激光捕获技术及其发展

激光捕获技术是利用光辐射力来捕捉、移动和操纵微粒的先进技术。光镊即单光束梯度力光阱是通过在高度会聚的激光束束腰附近所产生的极高的场强梯度来形成皮牛顿量级的力,可以三维地捕获和操纵微小粒子。阐述了激光捕获技术的模型和原理以及系统的基本结构;追踪了激光捕获技术的最新研究进展;介绍了非高斯型光阱、光纤光阱和全息光镊等几种特殊形式,并分析了每种形式的特点。展望了激光捕获技术的发展前景。     

光纤探针型近场光镊光阱力特性研究

基于动量守恒原理,结合麦克斯韦应力张量和三维时域有限差分方法,建立了近场空间内激光光镊对纳米微粒的光阱力计算模型.分析了光纤探针型近场光镊的近场分布以及操作纳米微粒时各轴向光阱力的分布情况,并探讨了光纤探针尖端的捕获尺寸、捕获位置和操作稳定性.结果表明:微粒应处于光纤探针针尖的近场空间内才可实现稳定可靠的纳米操作,不同尺寸的微粒具有不同的捕获效果,且随初始位置的不同微粒的捕获位置亦不同.计算结果为激光近场光镊纳米操作装置的设计和制造提供了理论基础.     

双层介质球体所受光作用力的分析与计算

计算了双层介质球体的光作用力.结果表明,双层结构内外层相对折秧经和相对厚度的变化都将影响光作用力的大小.特别是当内层折射率大于外层折射率时,减小内层半径可得到一较小区域,在此区域光镊系统刚度将得到有效提高,可实现对双层介质球体的稳定束缚;而当内层折射率小于外层折射率时,随内层半径的减小,介质小球可能有两个稳定平衡点出现.     

两种单光纤光镊捕获效果的数值仿真与实验研究

采用一种基于时域有限差分(FDTD)的数值算法,仿真计算了抛物线形和大锥角形两种新型单光纤光镊的出射光场,并在稳态场下通过对麦克斯韦应力张量积分求得介质球在两种光场中受到的光阱力,得到大锥角型光纤端产生的光阱力较大的结论;讨论了不同介质球大小、折射率,光纤探针形状对光阱力的影响.在实验中这两种光纤探针都实现了对水中酵母菌细胞的捕获,且采用流体力学法对抛物线形和大锥角形二种新型单光纤光镊产生的光阱力进行了标定.结果表明:基于FDTD数值仿真方法计算受力与实验结果一致,并且这种计算光纤光镊产生的光阱力的方法简单.适用;且抛物线形和大锥角形光纤探头都具备构成单光纤光镊的条件.     

光纤探针型近场光镊光阱力特性研究

基于动量守恒原理,结合麦克斯韦应力张量和三维时域有限差分方法,建立了近场空间内激光光镊对纳米微粒的光阱力计算模型.分析了光纤探针型近场光镊的近场分布以及操作纳米微粒时各轴向光阱力的分布情况,并探讨了光纤探针尖端的捕获尺寸、捕获位置和操作稳定性.结果表明:微粒应处于光纤探针针尖的近场空间内才可实现稳定可靠的纳米操作,不同...     

Systematical study of the trapping forces of optical tweezers formed by different types of optical ring beams

The technique of optical tweezers has been improved a lot since its invention, which extends the application fields of optical tweezers. Besides the conventionally used Gaussian beams, different types of ring beams have also been used to form optical tweezers for different purposes. The two typical kinds of ring beams used in optical tweezers are the hollow Gaussian beam and Laguerre--Gaussian (LG) beam. Both theoretical computation and experiments have shown that the axial trapping force is improved for the ring beams compared with the Gaussian beam, and hence the trapping stability is improved, although the transverse trapping forces of ring beams are smaller than that of Gaussian beam. However, no systematic study on the trapping forces of ring beam has ever been discussed. In this article, we will investigate the axial and transverse trapping forces of different types of ring beams with different parameters systematically, by numerical computation in which the ray optics model is adopted. The spherical aberration caused by the refractive index mismatch between oil and water is also considered in the article. The trapping forces for different objectives that obey the sine condition and tangent condition are also compared with each other. The result of systematical calculation will be useful for the applications of optical tweezers formed by different types of ring beams.     

Theoretical comparison of optical traps created by standing wave and single beam

We used generalised Lorenz–Mie scattering theory (GLMT) to compare submicron-sized particle optical trapping in a single focused beam and a standing wave. We focus especially on the study of maximal axial trapping force, minimal laser power necessary for confinement, axial trap position, and axial trap stiffness in dependency on trapped sphere radius, refractive index, and Gaussian beam waist size. In the single beam trap (SBT), the range of refractive indices which enable stable trapping depends strongly on the beam waist size (it grows with decreasing waist). On the contrary to the SBT, there are certain sphere sizes (non-trapping radii) that disable sphere confinement in standing wave trap (SWT) for arbitrary value of refractive index. For other sphere radii we show that the SWT enables confinement of high refractive index particle in wider laser beams and provides axial trap stiffness and maximal axial trapping force at least by two orders and one order bigger than in SBT, respectively.     

A study of multi-trapping of tapered-tip single fiber optical tweezers

We develop a pair of tapered-tip single fiber optical tweezers, and study its multi-trapping characteristic. The finite difference time domain method is employed to simulate the trapping force characteristic of this pair of single fiber optical tweezers, and the results show that the number of trapped particles depends on the refractive index and the size of the particles. The trapping force of this pair of tapered-tip single fiber optical tweezers is calibrated by the experimental method, and the experimental results are consistent with the theoretical calculation results. The multi-trapping capability realized by the tapered-tip single fiber optical tweezers will be practical and useful for applications in biomedical research fields.     

EFFECT OF SPHERICAL ABERRATION INTRODUCED BY WATER SOLUTION ON TRAPPING FORCE

Trapping force of an optical tweezers system with an oil immersion objective is calculated with a ray-optics model. Results indicate that the trapping force will be decreased as a result of the introduction of spherical aberration, which is caused by the refractive mismatch between objective oil and water, when the sample manipulated is suspended in a water solution. The effect of spherical aberration will be serious when the detection depth of the optical tweezers is enhanced.     

Improvement of the axial trapping effect using azimuthally polarised trapping beam

A dual optical tweezers system,which consists of a doughnut mode optical tweezer (DMOT) with the azimuthally polarised trapping beam and a solid mode optical tweezer (SMOT) with the Gauss trapping beam was constructed to compare the axial trapping effect of DMOT and SMOT.The long-distance axial trapping of ST68 microbubbles (MBs) achieved by DMOT was more stable than that of SMOT.Moreover the axial trapping force measured using the viscous drag method,was depended on the diameter of the particle,the laser power,and the numerical aperture (NA) of the objective lens.The measurement of the axial trapping force and the acquisition of CCD images of trapping effect confirmed that the DMOT showed excellent axial trapping ability than SMOT.A simple and effective method is developed to improve axial trapping effect using the azimuthally polarized beam as trapping beam.This is helpful for the long-distance manipulating of particles especially polarised biological objects in axial direction.