光的力学效应及光阱力的测量

介绍一个利用光镊技术直观地演示光的力学效应的实验。简要讨论了开设这一实验的背景和目的，给出了光镊原理、实验装置、光阱力的测量方法和实验安排。     

光镊力影响因素的计算分析

运用基于T矩阵算法的开源光镊计算工具包对可能影响光镊力的微粒尺寸、相对折射率以及光束模式进行了研究,计算结果表明,这三方面因素都会对光镊力产生显著影响,微粒直径与波长相等、相对折射率尽可能大时选择恰当的光束模式能够产生最佳的光镊捕获效果.     

轴向多光阱微粒捕获与实时直接观测技术

传统的光镊技术使用单个物镜同时进行光学捕获与显微成像,使得捕获与成像区域被限制在物镜焦平面附近,无法同时观察到沿光轴方向(即Z向)捕获的多个微粒.本文提出一种轴平面(XZ平面)GerchbergSaxton迭代算法来产生沿轴向分布的多光阱阵列,将轴平面成像技术与光镊结合,实现了沿轴向对二氧化硅微球的多光阱同时捕获与实时观测.通过视频分析法测量了多个二氧化硅微球在轴向光镊阵列中的布朗运动,并标定了光阱刚度.本文提出的轴向多光阱微粒捕获与实时观测技术为光学微操纵提供了一个新的观测视角和操纵方法,为生物医学、物理学等相关领域研究提供了一种新的技术手段.     

Trapping and controlled rotation of low-refractive-index particles using dual line optical tweezers

We show that dual line optical tweezers provides a convenient and dynamically reconfigurable approach for trapping and transport of low refractive index microscopic particles. By varying the spacing between the two line tweezers, particles of varying sizes could be trapped. Further, simultaneous rotation of the dual line tweezers could be used for controlled rotation of the trapped low-index particles. The transverse trapping force and the efficiency of the trap measured along the direction perpendicular to the line tweezers are in very good agreement with the theoretically estimated value. PACS 07.60.-j; 87.80.Cc; 87.80.Fe     

Beam optics approach to the ray optics model for the optical trapping efficiency of optical tweezers

Journal of the Korean Physical Society - The optical trapping efficiency of optical tweezers can be explained by the ray optics model when the particle size is much larger than the wavelength of...     

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.     

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.     

Spatial light modulators for the manipulation of individual atoms

We propose a versatile arrangement for the trapping and manipulation of single atoms in optical tweezers formed by the direct image of a spatial light modulator (SLM). The scheme incorporates a high numerical aperture microscope to map the intensity distribution of a SLM onto a cloud of cold atoms. The regions of high intensity act as optical dipole-force traps. With a SLM fast enough to modify the trapping potential in real time, this technique is well suited for the controlled addressing and manipulation of arbitrarily selected atoms.     

Resource Letter: LBOT-1: Laser-based optical tweezers

This Resource Letter provides a guide to the literature on optical tweezers, also known as laser-based, gradient-force optical traps. Journal articles and books are cited for the following main topics: general papers on optical tweezers, trapping instrument design, optical detection methods, optical trapping theory, mechanical measurements, single molecule studies, and sections on biological motors, cellular measurements and additional applications of optical tweezers.     

远场光钳与近场光钳的发展

以经典光学为基础的光钳技术(又称"光镊")在生物、物理和化学等领域得到了广泛的发展和应用,但是该技术受到高倍显微物镜的尺寸和光学衍射极限等多种因素的制约,从而限制了其进一步发展。而远场光纤光钳和近场光钳技术,从不同方面克服了传统光钳的局限。回顾了传统光钳、远场光纤光钳和近场光钳的发展,着重讨论了各种方法的工作原理、实验方法和技术性能,对这几种光钳技术进行了深入地总结和细致地比较。     

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)     

Experimental measurement and analysis of the optical trapping force acting on a yeast cell with a lensed optical fiber probe

Based on an optical trapping system with a single-lensed fiber probe inserted at an angle, the sub-picoNewton trapping force acting on a yeast cell as a function of the displacement is measured experimentally by the static and dynamic methods, respectively, whose measurement processes are presented in detail. The measured maximum trapping efficiency is 0.07 in our experiment, which is an order of magnitude lower than that of the optical tweezers. The characteristics of the trapping force in the various horizontal directions are discussed. Finally, the analysis of the measurement error shows the factors and their magnitude which cause error, and offers a way to reduce the error in future.     

Optical travelator: transport and dynamic sorting of colloidal microspheres with an asymmetrical line optical tweezers

We report the transport, funnelling and dynamic sorting of colloidal microspheres in an aqueous suspension using line optical tweezers with asymmetrical intensity profiles. The line tweezers readily trapped and propelled the microspheres along the length of the line tweezers. Using this simple technique, transporting and funnelling of microspheres within a microscopic region were demonstrated. To illustrate the dynamic particle-sorting capability of the line tweezers, a binary colloidal system comprising of microspheres with diameters of 1.1 μm and 3.2 μm were driven past the line tweezers by electrophoresis. As the optical trapping force is dependent on the size of the microspheres, the line tweezers was able to change the path of the larger spheres while exerting little influence on the smaller spheres thus sorting the two types of microspheres. At optimized laser power and flow rate of microspheres, sorting efficiency greater than 90% has been achieved. PACS 42.15.Eq; 87.80.Cc; 87.80.Fe; 82.70.Dd     

利用光镊计算工具箱实现光镊系统的参量评价

光镊所捕获的微球尺度常常落在中间尺度上,导致相关参量难于计算.OTT1光镊工具箱是一种基于广义Lorenz-Mie理论的T-matrix方法,它的发展使得对光镊系统的详细计算和评价成为可能.本文对光镊的轴向捕获特性曲线、线性性和刚度,以及杜克系列微球的互换性做了计算和评价.结果表明:光镊所用物镜的数值孔径越接近水的折射率捕获效果越好;0.8~1.2 μm的聚苯乙烯微球组成的光镊刚度较大;直径在2 μm以下的聚苯乙烯微球组成的光镊线性度较好;0.8~2 μm的Duke系列聚苯乙烯微球的互换性较好,便于纳米光镊的修正与实验;要避免米共振微球的直径要在2.5 μm以下.     

近场光镊技术研究新进展

光镊技术,又称光学捕获技术,它是利用光的辐射压力来捕获和操纵包括电介质颗粒、生物细胞及生物大分子在内的微小粒子的。近场光镊技术利用近场光学倏逝场随距离急剧衰减的特征,可显著地降低捕获粒子的尺寸,实现纳米捕获。追踪了近场光镊技术的最新进展,包括全内反射相干倏逝场、近场光学镀膜光纤探针尖、激光照明金属探针尖和聚焦倏逝场用于近场光学捕获,并对其进行了比较,分析了它们存在的主要问题和未来发展方向。     

Simple and high efficient graded-index multimode fiber tweezers:simulation and experiment

We propose and demonstrate a novel single fiber optical tweezer based on a graded-index multimode fiber(GIMMF), which works with a free length GIMMF(30 cm). We achieve a three-dimensional stable trap of yeast cells by using the GIMMF optical tweezers. Compared with the single-mode fiber optical tweezers,the GIMMF optical tweezers possess large optical trapping forces. Owing to the freedom of the GIMMF length,the fabrication of the GIMMF optical tweezers is simple, repeatable, and highly efficient. The GIMMF tweezers have the penitential to become a new member of the single fiber optical tweezers family and have a wide range of applications in the medical and biological cytology fields.     

Manipulation of Nanoparticles Using Dark-Field-Illumination Optical Tweezers with Compensating Spherical Aberration

Based on our previous investigation of optical tweezers with dark field illumination [Chin. Phys. Left. 25（2008）329] nanoparticles at large trap depth are better viewed in wide field and real time for a long time, but with poor forces. Here we present the mismatched tube length to compensate for spherical aberration of an oil-immersion objective in a glass-water interface in an optical tweezers system for manipulating nanoparticles. In this way, the critical power of stable trapping particles is measured at different trap depths. It is found that trap depth is enlarged for trapping nanoparticles and trapping forces are enhanced at large trap depth. According to the measurement, 70-nm particles are manipulated in three dimensions and observed clearly at large appropriate depth. This will expand applications of optical tweezers in a nanometre-scale colloidal system.     

光镊在生命科学中的应用

由于光镊具有无直接接触、无损伤等诸多优点,且光镊产生的力在皮牛顿量级,正好落在生物大分子相互作用力的范围,所以光镊在生物大分子相互作用测量方面取得了越来越广泛的应用.文章详细介绍了光镊的出现、发展过程以及在生命科学中代表性应用结果.这些结果表明,将光镊应用在生命科学领域,可以揭示或证实许多以前不曾深刻了解的生物大分子的活动规律与机制.     

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。     

泽尼克多项式校正全息阵列光镊像差的实验研究

像差会影响光镊对粒子的捕获效果. 全息阵列光镊中, 像差不仅来自光学元件, 由特定算法设计的光阱相位片也会在光路中引入像差. 本文通过液晶空间光调制器加载泽尼克多项式相位图, 对全息阵列光镊中由光栅透镜组型算法引起的像差进行校正. 结果显示: 利用三阶泽尼克多项式可有效消除光路中由光栅透镜组型算法引 起的慧差, 使得捕获2 μm聚苯乙烯小球的阵列光阱刚度提高了约40%; 对比不同项的像差校正结果发现, 全息阵列光镊中由算法引起的慧差 与光学元件引起的像差一样, 也会对阵列光阱的捕获效果产生较大影响; 同时根据一阶像差校正结果可得光栅透镜 组型算法对于一阶泽尼克像差具有鲁棒性. 实验结果表明, 对全息阵列光镊中由 算法引起的像差进行校正, 对于提高光阱的捕获效果和深化对算法特性的认识都具有重要意义.