基于T矩阵的激光光阱力计算

Computation of optical trapping force based on T-matrix method

在一定条件下,经过高数值孔径聚焦后的激光可以捕获大小从约几十纳米到几十微米范围内的微粒,这种技术叫做光镊,光镊技术广泛应用于许多生物领域。虽然光镊本身结构简单,用单光束就可以捕获单个粒子,但对光阱力的精确计算却存在一定的难度。虽然一些近似的方法如几何光学或瑞利假设可以用来进行光阱力的计算,但这些方法仅在一定限制范围内适用。本文把电磁散射理论作为一种通用的方法来解决光阱力的计算问题,论述了如何使用T矩阵方法进行光阱力计算并给出了一些数值结果,证明了T矩阵方法在光阱力计算方面的能力和效率。此外,本文还分析了一些对光捕陷效率的影响因素。

It has been proved that under certain conditions a single laser beam focused through an objective lens with high numerical aperture can trap microscopic particles in the size range from tens of nanometers to tens of micrometers. This technique is commonly referred to as an optical tweezers and is widely used in many biological applications. Despite the apparent simplicity of a laser trap, with a single particle in a single beam, exact calculation of the optical forces on particles is very difficult. Calculations can be performed using some approximate methods such as Ray-Opticsand Raleigh hypothesis, but are only applicable within their ranges of validity. We can obtain a general theory for laser trapping by applying the electromagnetic scattering theory. In this paper, we describe how the T-matrix approach can be used to computer optical trapping force and give some numerical results, and demonstrate the capabilities and effectiveness of the T-matrix approach in the calculation of the trapping forces. We also analyze some factors that may affect a successful optical trapping.