Simpson Stephen H, Hanna Simon
H.H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK.
J Opt Soc Am A Opt Image Sci Vis. 2010 Jun 1;27(6):1255-64. doi: 10.1364/JOSAA.27.001255.
Holographic optical tweezing permits the trapping of objects with less than spherical symmetry in appropriately distributed sets of beams thereby permitting control to be exerted over both the orientation and position. In contrast to the familiar case of the singly trapped sphere, the stiffness and strength of such compound traps will have rotational components. We investigate this for a simple model system consisting of multiply trapped dielectric cylinder. Optically induced forces and torques are evaluated using the discrete dipole approximation and the resulting trap stiffnesses are presented. A variety of configurations of trapping beams are considered. Hydrodynamic resistances for the cylinder are also calculated and used to estimate translation and rotation rates. A number of conclusions are reached concerning the optimal trapping and dragging conditions for the rod. In particular, it is clear that it is advantageous to drag a rod in a direction perpendicular rather than parallel to its length. In addition, it is observed that the polarization of the incident light plays a significant role. Finally, it is noted that the non-conservative nature of the optical force field manifests itself directly in the stiffness of the trapped cylinder. The consequences of this last point are discussed.
全息光镊能够在适当分布的光束组中捕获具有非球对称形状的物体，从而可以对其方向和位置进行控制。与单个捕获球体的常见情况不同，这种复合光阱的刚度和强度将具有旋转分量。我们针对由多个捕获的介质圆柱体组成的简单模型系统对此进行研究。使用离散偶极近似法评估光诱导力和扭矩，并给出由此产生的光阱刚度。考虑了多种捕获光束的配置。还计算了圆柱体的流体动力学阻力，并用于估计平移和旋转速率。得出了一些关于杆的最佳捕获和拖动条件的结论。特别是，很明显，沿垂直于杆长而非平行于杆长的方向拖动杆是有利的。此外，观察到入射光的偏振起着重要作用。最后，需要指出的是，光力场的非保守性质直接体现在被捕获圆柱体的刚度上。讨论了最后这一点的影响。
