Simpson Stephen H, Hanna Simon
H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol, BS8 1TL, UK.
Opt Express. 2011 Aug 15;19(17):16526-41. doi: 10.1364/OE.19.016526.
The accuracy of the discrete dipole approximation (DDA) for computing forces and torques in optical trapping experiments is discussed in the context of dielectric spheres and a range of low symmetry particles, including particles with geometric anisotropy (spheroids), optical anisotropy (birefringent spheres) and structural inhomogeneity (core-shell spheres). DDA calculations are compared with the results of exact T-matrix theory. In each case excellent agreement is found between the two methods for predictions of optical forces, torques, trap stiffnesses and trapping positions. Since the DDA lends itself to calculations on particles of arbitrary shape, the study is augmented by considering more general systems which have received recent experimental interest. In particular, optical forces and torques on low symmetry letter-shaped colloidal particles, birefringent quartz cylinders and biphasic Janus particles are computed and the trapping behaviour of the particles is discussed. Very good agreement is found with the available experimental data. The efficiency of the DDA algorithm and methods of accelerating the calculations are also discussed.
在光学捕获实验中，针对计算力和扭矩的离散偶极近似（DDA）的准确性，在介电球体以及一系列低对称性粒子的背景下进行了讨论，这些粒子包括具有几何各向异性（椭球体）、光学各向异性（双折射球体）和结构不均匀性（核壳球体）的粒子。将DDA计算结果与精确的T矩阵理论结果进行了比较。在每种情况下，两种方法在预测光力、扭矩、阱刚度和捕获位置方面都取得了极好的一致性。由于DDA适用于对任意形状粒子的计算，因此通过考虑最近受到实验关注的更一般系统来扩展这项研究。特别是，计算了低对称性字母形状的胶体粒子、双折射石英圆柱体和双相Janus粒子上的光力和扭矩，并讨论了粒子的捕获行为。与现有的实验数据取得了非常好的一致性。还讨论了DDA算法的效率以及加速计算的方法。
